2000: An Evolutionary Manifesto
AN EVOLUTIONARY MANIFESTO:
A NEW HYPOTHESIS FOR ORGANIC CHANGE
by John A. Davison, Ph.D.
THIS TREATISE IS DEDICATED TO THE MEMORY OF SIX GREAT SCIENTISTS
William Bateson
Leo S. Berg
Robert Broom
Richard B. Goldschmidt
Pierre Grassé
Otto Schindewolf
A dwarf standing on the shoulders of a giant
may see farther than a giant himself.
— Robert Burton
No sadder proof can be given by a man of his own littleness
than disbelief in great men.
— Thomas Carlyle
CONTENTS
PREFACE
I. INTRODUCTION
1. Why has Darwinism prevailed?
2. Living and nonliving systems compared
3. The evidence from paleontology
4. Sexual and asexual reproduction compared
5. The failure of selection
6. Can sexual forms evolve?
III. IT IS NOT THE GENES BUT THE CHROMOSOMES THAT DO THE EVOLVING
1. Chromosome structure and evolution
2. Why is evolution irreversible?
3. The first meiotic division
4. Position effects and primate evolution
IV. SEXUAL REPRODUCTION LIMITS EVOLUTIONARY CHANGE
1. The independent origins of sexual reproduction
2. The importance of nonhomology
3. Semi-meiosis and the origin of diploidy
4. Semi-meiosis in birds
5. Sex reversal in birds and amphibians
6. Semi-meiosis and genetic variability
V. THE FAILURE OF THE DARWINIAN HYPOTHESIS
1. Darwin’s finches
2. The evidence from cytogenetics
3. A hypothetical reconstruction of evolutionary history
VI. GRADUALISM VERSUS SALTATIONISM
1. The fossil record
2. The significance of the individual in macroevolution
VII. ORDER VERSUS CHAOS
1. Are there laws governing evolution?
2. Epigenesis and preformation
3. Ontogeny and phylogeny compared
4. The rate of evolution
5. Has evolution been guided?
VIII. CONCLUSION
This work represents an elaboration of material presented by the author in courses offered here at the University of Vermont, especially Biology 255, The Comparative Physiology of Reproduction and Biology 202, Quantitative Biology. It is my hope that this treatise will reach not only the professional biologist but all others
who realize how little we really understand concerning the history of life on this planet. I have assumed little in the way of background and I have defined most technical terms as they appear. The basic ideas put forth here were first published in 1984. I hope that this expanded and more completely documented treatment will reach a larger
and more receptive audience.
My own background is in General and Developmental Physiology which is to say that I am interested in how things work. Like others before me, I have come to the realization that Darwinism simply does not work. That conclusion has led to a series of questions which I pose and attempt to answer. Answering one question often leads to asking
another. Only by asking questions is one compelled to provide answers. I employ that approach throughout this presentation.
Among those questions are the following: Is evolution finished? Is sexual reproduction incapable of supporting evolutionary change? Is selection, natural or artificial, incapable of producing new life
forms? In contrast to the Darwinian view, has evolution proceeded by means of leaps (saltation) rather than gradually through intermediate forms? Is there an alternative to Darwinism which, unlike that
hypothesis, is compatible with all the facts revealed by paleontology, embryology, cytology, taxonomy, physiology and genetics? Do internal factors have a role in evolution? Is evolution irreversible? Is the
individual, rather than the population, the instrument of evolutionary change? Are there laws governing evolution? Is there compelling evidence that evolution (phylogeny), like the development of the
individual (ontogeny), involves the release or derepression of preformed information? Finally, the most controversial question of all: Has evolution been guided? With the exception of the last question, to which no certain answer will probably ever be given, I will answer yes to each of these questions.
I realize these claims will seem outrageous to the doctrinaire Darwinian. I can only explain that I have not arrived easily at these convictions but have been driven to them through a host of incontrovertible realities that demand those responses. I ask only that the evidence be heard.
I cannot overemphasize the debt that I owe to my many predecessors,
especially those six to whom I dedicate this work. Their monumental
contributions speak for themselves and they should be given serious
consideration by every thinking person. Without them I would have
been unable to proceed. Whenever possible, I quote them directly so
there can be no misunderstanding about what they meant. Most of the
quotations from authors not in the cited literature are from the
sixteenth edition of Bartlett’s Familiar Quotations.
I owe a very special debt to Dr. Judith Van Houten, Chair of the
Department of Biology and Associate Dean of the College of Arts
and Sciences. In addition to freezing my salary, her continuing
and largely successful attempts to isolate me from the students
have served only to provide me with a powerful incentive to continue
the search for the truth concerning the great mystery of Evolution.
We are once more reminded of the profound significance of Arnold
Toynbee’s celebrated aphorism:
The Virtues of Adversity
AN EVOLUTIONARY MANIFESTO:
A NEW HYPOTHESIS FOR ORGANIC CHANGE
by John A. Davison, Ph.D.
New opinions are always suspected and usually opposed,
without any great reason but because they are not already
common.
— John Locke
The decisive step in evolution, the first step toward
macroevolution, the step from one species to another, requires
another evolutionary method than that of sheer accumulation of
micromutations.
— Richard B. Goldschmidt
I begin with the very last words in Darwin’s Origin of Species:
… endless forms most beautiful and most wonderful have
been, and are being, evolved.
I will show that the last three words are without foundation for the
vast majority of higher life forms, both those which have existed in
the past as well as those which are still extant today. I am aware
of the effect of such an assertion and I am delighted to accept the
responsibility of demonstrating its validity.
Several years ago, when I was still teaching introductory biology,
a rumor got started among the students that I didn’t believe in
evolution. I finally responded in lecture by indicating that the
rumor was entirely correct. I told the students that I did not
“believe” in evolution; I knew that it had occurred. I hoped
by this means to impress upon the students the difference between
matters of belief (faith) and matters of knowledge. Darwinism is a
matter simply of belief since the progressive evolution of no creature
now living has ever been demonstrated. As an experimentalist I am not
impressed by unconfirmed hypotheses and accordingly I began casting
about for possible explanations for this remarkable state of affairs.
Accepting the reality that evolution has occurred leads to the
question as to whether or not it is still occurring and, if not,
why not? I will present a substantial body of evidence indicating
that the evolution of higher organisms is at a virtual standstill,
a conclusion that had been reached by others long before me.
Let me take this opportunity to acknowledge the huge debt that we
all owe to some of the greatest biologists of the twentieth century.
Among them are the Russian ichthyologist and zoogeographer Leo S.
Berg (1876-1950), the geneticists Richard B. Goldschmidt (1878-1958)
and William Bateson (1861-1926), the paleontologists Otto Schindewolf
(1896-1971) and Robert Broom (1866-1951) and the French zoologist
Pierre Grassé (1895-1985). Each is a widely acclaimed scholar of the
first rank and not one could be described as an armchair theoretician.
They had each disclosed major difficulties with the Darwinian model
and had discussed them at great length in their books and papers.
I am very pleased to be able to consolidate and incorporate many of
their common and often independent conclusions into a new hypothesis
of organic evolution. This is a truly international assemblage of
investigators with Otto Schindewolf coming from Germany, Robert Broom
from Scotland and later South Africa, Leo Berg from Russia, Pierre
Grassé from France, William Bateson from England and Richard
Goldschmidt, a naturalized American who escaped Nazi Germany.
All the more remarkable then is the unity of their perspectives
on the complete failure of the Darwinian hypothesis.
By way of contrast, Ernst Mayr, in his opus magnus, The Growth of
Biological Thought (1982), deals with these six skeptics as follows.
Broom is not even mentioned. The books by Grassé (1973) and Berg
(1969) are listed in the bibliography, but no reference to either
author is made in the text. Goldschmidt and Schindewolf are dispensed
with in a few words. Only Bateson is given a remotely even-handed
treatment. Perhaps it is understandable why Mayr shortchanged
these scientists since on page 132 he made his position indelibly
plain (literally) by describing himself as a “dyed-in-the-wool
Darwinian”!
The new mechanism, which I have called the semi-meiotic hypothesis,
is based upon an obvious fact that has been before us for a very long
time. It has to do with the manner in which the sex cells, the eggs
and sperm, are formed. This process, known as meiosis or chromosome
reduction, occurs in two steps. Prior to the first meiotic division
the chromosomes become duplicated as they do in mitosis. Then two
divisions take place. The first returns the chromosome number to
the diploid state and so can be considered to be a form of diploid
presexual reproduction. This first division takes place in a special
way which I feel provides the mechanism of macroevolution. Also since
the second division cannot occur until the first has taken place, the
first meiotic division is logically the more primitive of the two
and accordingly must have evolved first (Davison 1984 1993 1998).
Upon this premise I proceed.
II. Is evolution finished?
All intelligent thoughts have already been thought;
what is necessary is only to try to think them again.
— Goethe
It is undesirable to believe a proposition when there
is no ground whatsoever for supposing it to be true.
— Bertrand Russell
II – 1. Why has Darwinism prevailed?
Darwinism has prevailed entirely for negative reasons since alternative hypotheses have proven to be inadequate. Chief among these is Lamarckism or the genetic transmission of characters acquired during the life of the individual. Such transmissions have never beendemonstrated at least in higher forms. Accordingly, in the absence of experimental verification, Lamarckism cannot be given serious consideration.
A second alternative view is Creationism. Here caution must be observed. While it is true that the existence of a Creator, while a logical necessity, has never been rigorously proved and perhaps never can be, it is also true that neither has been the spontaneous generation of life. Pasteur’s flasks, on display at the Sorbonne and open to the air, remain sterile to this day and there is no evidence whatsoever from the geological record to support the celebrated “organic soup” hypothesis for spontaneous generation.
Perhaps the most compelling feature for the Darwinists resides in their persistent conviction that all of evolution is the result of blind chance. In so doing, the Darwinists refuse to consider that evolution might be subject to laws and precise mathematical relationships such as those that govern virtually every aspect of the inanimate world. Obvious examples are Galileo’s Law of Falling Bodies, Newton’s Laws of Motion and Einstein’s equation of energy and mass. One must be prepared to realize that there may be comparable laws at work in the living world. Furthermore, blind chance demands that life should have arisen and should still be arising on countless other planets in the vast cosmos, yet there is no evidence that life exists now, or has ever existed anywhere, except on this planet. With all our advanced technology, we still have not been able to
produce even the simplest organic system which could even remotely be described as being alive. Are we to believe that mere chance can accomplish that which has proven quite impossible for the enlightened scientist to achieve? I regard that notion as absurd! I quote Albert Einstein on the matter of chance: “I shall never believe that God plays dice with the world.”
If Einstein’s physical world does not operate through chance, would one really expect the living world to do so? I, as others before me, do not think so.
The Darwinists’ stubborn refusal to consider any possible role for laws, order and purpose is what primarily accounts for their failure to present a rational mechanism for evolutionary change. Technically, Darwinism is not even a theory. It is only a hypothesis which, to this day, remains totally devoid of experimental and descriptive verification. Theories, sensu strictu, are hypotheses which, having been tested, have been found valid. For example, Einstein’s Special Theory of Relativity remained a hypothesis until it had been verified. Only then did it become a theory.
Scientists, after all, are expected to maintain open minds. But do they? Sadly, I must answer that question — Not always!
II – 2. Living and nonliving systems compared
One of the most influential of Darwin’s predecessors was the geologist Charles Lyell. He expounded the concept of uniformitarianism. Stated simply, he believed that the forces we now see gradually reshaping the surface of the earth have operated the same way throughout the past. This idea gave Darwin the necessary timescale to account for the gradual evolution of the life forms we now see. His total acceptance of the uniformitarian doctrine is clearly evident in those closing words of the Origin which I quoted in the introduction: “… have been, and are being, evolved”.
Can the notion of uniformitarianism be applied to living systems? The answer at every level is a resounding no. A muscle cell, having contracted, must relax before it can contract again. An amoeba grows and then it stops to divide before it recommences growth. Embryos undergo cellular differentiation, then stop when the definitive state is reached. Most creatures grow until they reach adult size and then stop. In other words, living systems practice autoregulation and
self-limitation. These are fundamental distinctions between the animate and inanimate worlds (Davison 1998).
I now present the evidence that evolution, like other biological processes, has also been subject to autoregulation.
II – 3. The evidence from paleontology
The question — Is evolution finished? — like all others concerning evolution, must ultimately be reconciled with the fossil record. I have no credentials as a paleontologist, so I will offer the views of two authorities, the first a professed Darwinian and the second a skeptic of Darwinism. Julian Huxley, the grandson of Thomas Henry Huxley, published what unfortunately proved to be an excessively influential book in 1942. Evolution: The Modern Synthesis summarized a consensus among certain geneticists, systematists and paleontologists that evolution was a Darwinian phenomenon, guided by chance and natural selection. Among these were the geneticist Theodosius Dobzhansky, the ornithologist Ernst Mayr and the
paleontologist George Gaylord Simpson. Perhaps the most remarkable feature of the text is the revealing and totally contradictory summary that Huxley offers on page 571, seven pages from the end.
Evolution is thus seen as a series of blind alleys. Some are extremely short — those leading to new genera and species
that either remain stable or become extinct. Others are longer — the lines of adaptive isolation within a group
such as a class or subclass, which run for tens of millions of years before coming up against their terminal blank wall.
Others are still longer — the links that in the past led to the development of the major phyla and their highest
representatives; their course is to be reckoned not in tens but in hundreds of millions of years. But all in the long
run have terminated blindly. That of the echinoderms, for instance, reached its climax before the end of the Mesozoic.
For arthropods, represented by their highest group, the insects, the full stop seems to have come in the early
Cenozoic. Even the ants and bees have made no advance since the Oligocene. For the birds, the Miocene marked
the end; for the mammals the Pliocene.
Note Huxley’s language: blind alley, terminal blank wall, terminated blindly, full stop and marked the end. Is this
language compatible with the Darwinian perspective? Of course it isn’t!
Robert Broom, who was certainly no Darwinian, had reached comparable conclusions:
There is, however, no doubt that evolution, so far as new groups are concerned, is at an end. That a small line of
The Coming of Man (1933)
generalized animals should have continued on till in Eocene times the Primates originated and then ceased, and that
except for specializations of Eocene types there has been no evolution in the last forty million years, and that the
evolutionary clock has so completely run down that it is very doubtful if a single new genus has appeared on earth
in the last two million years …
In Eocene times — say between 50,000,000 and 30,000,000 years ago — small primitive mammals rather suddenly gave
rise to over a dozen very different Orders — hoofed animals, odd-toed and even-toed, elephants, carnivores, whales,
rodents, bats and monkeys. And after this there were no more Orders of mammals ever evolved. There were great varieties
of evolution in the Orders that had appeared, but strangely enough Nature seemed incapable of forming any more new Orders. What is equally remarkable, no new types of birds appear to have evolved in the last 30,000,000 years. And most
remarkable of all, no new family of plants appears to have evolved since the Eocene. All major evolution has apparently
come to an end. No new types of fishes, no groups of molluscs, or worms or starfishes, no new groups even of
insects, appear to have been evolved in these latter
30,000,000 years.
Finding the Missing Link
(1951), page 107
Only once — perhaps in Cambrian times — did an invertebrate
give rise to a vertebrate, and the invertebrate ancestor
seems to have early become extinct. And today, there is
no invertebrate that could again give rise to a vertebrate.
“Evolution as the paleontologist sees it” (1932), page 68
There are no mammals today in the world that are not already specialized so far that they can never evolve into anything
very different.
Ibid., page 69
In a demonstration of his faith, Broom continued:
As evolution has practically finished and cannot be repeated unless all higher life is wiped off the earth and a new start
Ibid., page 71
made from the very beginning, we may perhaps conclude that man is the end to which some power has guided evolution.
I discovered that Broom and Huxley had corresponded on this matter
as early as 1933 as revealed by the following:
And a few zoologists are beginning to recognize that evolution
is slowing down, if not quite stopped. In a letter I had
from Professor Julian Huxley only a few months ago he says,
“I have often thought about your idea of the fading out of
evolutionary potency, and though I cannot pretend to agree
with some of the philosophical corollaries which you draw from
it, I more and more believe that it is of great importance as
a fact.”
“Evolution — Is there intelligence
Behind It?” (1933), page 14
While Huxley shared Broom’s scientific conclusions, it is not
surprising that as a humanist (as opposed to a deist) he did not
agree that evolution may have been guided. Nevertheless, one might
ask — If it has not been guided, then why has it stopped? I address
the question of guidance in a later section.
Without mentioning either Huxley or Broom, the French zoologist Pierre
Grassé reached the same conclusion. Curiously, the following comments
by Grassé (with which I agree completely) stand in marked contrast
to the title of the book which is their source!
Facts are facts; no new broad organizational plan has appeared
for several hundred million years, and for an equally long
time numerous species, animal as well as plant, have ceased
evolving. … At best, present evolutionary phenomena are
simply slight changes of genotypes within populations, or
substitution of an allele with a new one.
Evolution of Living Organisms
(1977), page 84
In order to proceed I am going to accept the consensus of Huxley,
Broom and Grassé that evolution has indeed ceased, at least for the
majority of higher life forms. Thus, intrinsic to the evolutionary
process itself has been the capacity to bring it to a halt, thereby
demonstrating autoregulation. One might now ask — Is it possible
to observe, and thereby explain, a mechanism that is no longer in
operation? To this question I answer — Of course not, which means
that one must attempt to reconstruct that mechanism from contemporary
observations. That reconstructive synthesis is a primary goal of this
treatise.
Another feature of evolutionary history bears on the question of
autoregulation. The vast majority of all the organisms that ever
existed have become extinct. I propose that they became extinct
because they could no longer evolve or otherwise manage to
survive. Isn’t it interesting that today we see rampant extinction,
and the list of endangered species continues to grow, yet no one has
observed the progressive evolution of any one of these forms as a
response to the challenges offered by a changing environment.
Admittedly, man is altering the environment at an unprecedented rate.
Aren’t these precisely the conditions that should be evoking dramatic
evolutionary responses? Where are they?
II-4. Sexual and asexual reproduction compared
While sexual reproduction is characteristic of most higher plants and
animals, it is by no means universal. Many plants and animals do not
practice sex and reproduce exclusively asexually. Every phylum in
both the animal and plant kingdoms has representatives that reproduce
asexually or, as it is also described, parthenogenetically or
gynogenetically. In the majority of these cases parthenogenesis is
essentially mitotic with the offspring being genetic replicas (clones)
of the parent. Why is this very conservative form of reproduction so
commonplace? Here is one suggestion. Sexual reproduction involves
the segregation and recombination of those genes contained in the two
parental organisms. Frequently the new combinations prove to be
inferior to those of the parents. Clonal (mitotic) parthenogenesis
precludes this possibility. Such creatures have no known means of
genetic recombination and accordingly would seem incapable of adapting
to a changing environment, yet many of them have been eminently
successful, enduring unchanged perhaps even for millions of years.
Why change the genome if it has already successfully established its
capacity to grow and reproduce? The single-celled Amoeba presents
an interesting example. This animal manages famously. As long as
it can reproduce faster than it acquires deleterious mutations it can
survive indefinitely and unchanged. The same can be said for many
other life forms in both the plant and animal kingdoms and of course
for the prokaryotes (bacteria and blue-green algae) as well.
The evidence that evolution may be finished coupled with the fact that
so many organisms reproduce sexually raises a provocative question –
can sexual forms evolve? Before I supply an answer to that question,
here are some relevant observations.
II-5. The failure of selection
[Selection] cannot, therefore, be an agency for the production
of new forms.
— Leo S. Berg
[Selection] acts more to conserve the inheritance of the species
than to transform it.
— Pierre Grassé
Man has practiced intensive selection for centuries, yet has failed
to produce new species by this means. Most parthenogenetic forms
offer little or nothing to select and so nearly all of man’s efforts
have been with creatures which reproduce sexually. Dogs present an
instructive example. In addition to the many working breeds, man has
produced some bizarre creatures like the Chihuahua and the Dachshund
as well as giant animals like the Great Dane, the Mastiff and the
Saint Bernard. Great variations in color, coat quality and even
temperament have also been produced. These differences are due to
the action of Mendelian genes segregating and recombining in sexual
reproduction. The result is that the products are able to interbreed
not only with each other but with the wolf as well. The hybrids are
fertile which is to say that they are not physiological hybrids at
all, indicating that no real evolution has taken place. It should
also be noted that selection, when carried to the extreme, invariably
results in a loss of fitness as is so obvious for example in the
shortened life spans of the Saint Bernard, the Great Dane and the
English Bulldog.
The Danish biologist Ojvind Winge described an interesting test of
speciation in his book Inheritance in Dogs. A male Saint Bernard
spontaneously mated with a female Dachshund which subsequently
delivered a litter. One member of this litter became pregnant and
delivered a normal litter herself proving that no real speciation had
occurred during the long period of separation of the parental breeds.
This female had, however, inherited her large body from the Saint
Bernard sire but the short legs from the Dachshund bitch with the
result that her belly dragged on the ground during her pregnancy
and had to be protected with towels! (Winge 1950, page 44.)
An even more impressive example of the failure of selection is
offered by the goldfish. Starting with the Asiatic carp Carassius
auratus, the Chinese and Japanese have derived some strange
creatures such as those with telescopic eyes some of which even gaze
upward as in the variety “celestial”. They have even produced forms
which depart from the fundamental vertebrate character of possessing
two pairs of lateral appendages, the pectoral and pelvic fins,
corresponding to our arms and legs respectively. By duplicating the
anal fin they converted the fish to a potential hexapod! They also
duplicated the caudal fin, a condition unknown in the natural world
and even suppressed the dorsal fin, a basic character in virtually all
fishes. The variety “celestial” combines all of these features and is
blind as well. None of this has produced any semblance of speciation
and the animals are still Asiatic carp.
Why do these attempts fail? Apparently they fail because they
represent the selection for individual mutant genes, from which one
can draw the formal conclusion that such alterations may have little
or nothing to do with the evolutionary process. It should also be
noted that dogs and goldfish reproduce only by sexual means.
In his remarkable book Nomogenesis; or, Evolution Determined by Law
(Russian edition 1922, English edition 1969) Leo Berg quotes the
American paleontologist Henry Fairfield Osborn on selection:
In all the research since 1869 on the transformations observed
in closely successive phyletic series no evidence whatever,
to my knowledge, has been brought forth by any paleontologist,
either of the vertebrated or invertebrated animals, that the
fit originates by selection from the fortuitous.
Osborn, quoted in Nomogenesis
(1969), page 127
In the same volume, on page 314, Berg cites R.C. Punnett, who
originated the familiar Punnett square for the solution of problems
in Mendelian segregation and recombination. From Punnett’s book on
mimicry:
Natural selection is a real factor in connection with mimicry,
but its function is to conserve and render preponderant an
already existing likeness, not to build up that likeness
through the accumulation of small variations, as is so
generally assumed.
Mimicry in Butterflies
(1915), page 152
Berg’s own views are expressed as follows:
An organism is a stable system, in which a tendency toward
variation is confined within certain limits by inheritance.
This truth is self evident. It would be impossible to
conceive how such complex organs as the eye, the ear or the
pituitary body could properly exercise their functions, if
they were the seat of an infinite number of variations, from
which it would be left to chance to select the most efficient.
Nomogenesis, page 27
The laws of the organic world are the same, whether we are
dealing with the development of an individual (ontogeny) or
that of a paleontological series (phylogeny). Neither in
the one nor in the other is there room for chance.
Ibid., page 134
William Bateson had offered, even before 1900, a similar appraisal
of selection:
For the crude belief that living beings are plastic
conglomerates of miscellaneous attributes, and that order
of form or Symmetry have been impressed upon this medley by
Selection alone; and that by Variation any of these attributes
may be subtracted or any other attribute added in indefinite
proportions, is a fancy which the Study of Variation does not
support.
Materials for the Study of
Variation (1894), page 80
The many converging lines of evidence point so clearly to
the central fact of the origin of the forms of life by an
evolutionary process that we are compelled to accept this
deduction, but as to almost all the essential features,
whether of cause or mode, by which specific diversity has
become what we perceive it to be, we have to confess an
ignorance nearly total. The transformation of masses of
population by imperceptible steps guided by selection, is,
as most of us now see, so inapplicable to the facts, whether
of variation or of specificity, that we can only marvel both
at the want of penetration displayed by the advocates of such
a proposition, and at the forensic skill by which it was
made to appear acceptable even for a time.
Problems of Genetics (1913), page 248
And it is apparently still considered to be acceptable by the majority
of evolutionary biologists. I am quite unable to understand how that
can be.
I agree with all of the foregoing by concluding that the primary
effect of natural selection is to prevent change. In so doing,
I do not challenge the reality of natural selection; I merely point
to its transparent failure as a progressive evolutionary device.
On the other hand, one must accept the fact that it is Nature that
ultimately does the selecting. Since new life forms have obviously
been allowed to persist, at least for a while, the question becomes
simply — How have new forms been produced, sexually or by some
other means? This consideration leads to the next question.
II-6. Can sexual forms evolve?
Nothing is so firmly believed as what is least known.
— Montaigne
I am by no means the first to question the capacity of sexual
reproduction to support significant evolutionary change. The
horticulturist Luther Burbank was not an academician; he claimed
to have received his education at the University of Nature.
From his autobiography:
There is a law of which I have not yet spoken that is useful
to plant-breeders, as well as being a limitation on them.
It is called the “Law of the Reversion to the Average”.
I know from my experience that I can develop a plum half
an inch long or one two and a half inches long, with every
possible length in between, but I am willing to admit that
it is hopeless to try to get a plum the size of a small pea,
or one as big as a grapefruit. I have daisies on my farm
little larger than my finger nail and some that measure six
inches across, but I have none as big as a sunflower, and
never expect to have. I have roses that bloom pretty steadily
for six months in the year, but I have none that will bloom
twelve, and I will not have. In short, there are limits to
the developments possible, and these limits follow a law.
But what law, and why?
It is the law that I have referred to above. Experiments
carried on extensively have given us scientific proof of what
we had already guessed at by observation; namely, that plants
and animals all tend to revert, in successive generations,
toward a given mean or average. Men grow to be seven feet
tall, and over, but never to ten; there are dwarfs not higher
than 24 inches, but none that you can carry in your hand …
In short, there is undoubtedly a pull toward the mean which
keeps all living things within some more or less fixed
limitations.
Partner of Nature (1939), page 92
Note that Burbank did not even consider the prospect of creating a new
species. His comments are reminiscent of the quaint eight-word poem
by Gertrude Stein: “A rose is a rose is a rose.”
It is useful, before presenting my next skeptic, to place
Darwinism in historical perspective. In 1900 Gregor Mendel’s work
was rediscovered and with it a great impetus was given to Darwinism.
With the recognition of Mendel’s factors, which we now know as genes,
variation among the individuals of a species was no longer a mystery.
A major exponent of the new science was William Bateson, now regarded
as the founder of modern genetics (he coined the term himself).
His enthusiasm for Mendelism was such that he named his newborn son
Gregory in 1904. However, that enthusiasm faded toward the end of
his life, as Gregory would recount to Arthur Koestler in 1970.
By 1924, [William] Bateson had come to realize, and told his
son in confidence, “that it was a mistake to have committed
his life to Mendelism, that this was a blind alley which would
not throw any light on the differentiation of species, nor on
evolution in general.”
The Case of the Midwife Toad
(1971), page 121
I feel that this is one of the most significant comments in all of
the evolutionary literature, and it is one with which I totally agree.
It is a testimony to the greatness of Bateson that he had the insight
to recognize and the courage to admit that failure. Mendelism is, of
course, the genetics associated with sexual reproduction, and here we
have Burbank and Bateson independently challenging the capacity
of that process to result in significant evolutionary change.
Note Bateson’s use of the expression blind alley.
Thus, when asked the question — Can sexual forms evolve? — one is
compelled, on the basis of an overwhelming body of negative evidence,
coupled with virtually no positive evidence, to answer — No, they
cannot evolve. This leads to other questions. Is there a kind of
reproduction other than the familiar sexual or Mendelian variety
and could this alternative mode be an effective evolutionary device?
As will become apparent, the answer to these two questions is yes.
III. It is not the genes but the chromosomes that do the evolving
We have long been seeking a different kind of evolutionary process
and have now found one; namely, the change within the pattern of the
chromosomes. … The neo-Darwinian theory of the geneticists is no
longer tenable.
— Richard B. Goldschmidt
III-1. Chromosome structure and evolution
One of the first to recognize the evolutionary significance of
chromosome structure was the geneticist Richard B. Goldschmidt.
In 1940, two years before Huxley’s Evolution: The Modern Synthesis,
Goldschmidt published The Material Basis of Evolution, based on
the Silliman lectures he had delivered at Yale University. It is
difficult to imagine two books more dissimilar while dealing with
the same subject. Goldschmidt’s book is divided into two sections,
the first dealing with what he called microevolution, the second
with macroevolution. His first section ends with this statement
so reminiscent of Bateson:
Subspecies are actually, therefore, neither incipient species
nor models for the origin of species. They are more or less
diversified blind alleys within the species. The decisive
step in evolution, the first step toward macroevolution,
the step from one species to another, requires another
evolutionary method than the sheer accumulation of
micromutations.
Note Goldschmidt’s use of the term blind alley, a characterization
offered independently by both Huxley and Bateson.
Twelve years later, Alexander Petrunkevitch endorsed Goldschmidt’s
view on speciation and again employed the term blind alley:
Without prejudice toward the studies on such animals
as Drosophila, I believe that Goldschmidt is right
when he considers microevolution to be a “blind alley”.
All morphological evidence is in favor of the assumption
that macroevolutionary changes in the Diptera were
completed in the comparatively distant past.
“Macroevolution and the fossil
record of Arachnida” (1952)
The “other method” to which Goldschmidt refers is the reordering of
existing genetic information within the structure of the chromosome.
Alterations in genic expression resulting from such rearrangements
are called position effects. In his words at the end of the section
on macroevolution:
The fact remains that an unbiased analysis of a huge body
of pertinent facts shows that macroevolution is linked to
chromosomal repatterning and that the latter is a method
of producing new organic reaction systems, a method which
overcomes the great difficulties which the actual facts raise
for the neo-Darwinian conception as applied to macroevolution.
The Material Basis of Evolution
(1940)
There are several kinds of chromosome rearrangements. Two chromosomes
can fuse together to form one or a chromosome can dissociate to form
two. Two breaks can occur along a chromosome with the broken fragment
undergoing a 180-degree rotation before reattaching. There are two
types of such inversions depending upon where in the chromosome they
occur. Each chromosome has somewhere along its length a place where
the spindle fibers attach during mitosis and meiosis. This structure,
called the centromere, contains DNA and, like the chromosome is also
self-replicating. If the centromere is within the inverted segment it
is called a pericentric inversion. If the inversion does not include
the centromere it is termed a paracentric inversion. Another type
of restructuring is reciprocal translocation in which two different
chromosomes exchange parts. Other types of changes include
duplications and deficiencies. Alterations can also occur in the
number and position of nucleolar organizers as well as changes in
the chromosome ends or telomeres.
Before proceeding I will briefly discuss the irreversibility of
evolution as it relates to chromosome structure.
III-2. Why is evolution irreversible?
The curve of evolution demonstrates that it is the result of a
series of irreversible historical phenomena.
— Pierre Grassé
If we look closely at this truly historical character of evolution
and the uniqueness of its individual stages, irreversibility appears
simply as a “self-evident” truth.
— Otto Schindewolf
Once more we witness identical conclusions, this time by Grassé, a
Frenchman and Schindewolf, a German, with neither referring to the
other.
No mammal has ever evolved into a reptile, no reptile into an
amphibian and no amphibian has ever evolved into a fish. There is
not a single documented example of a reversible evolutionary event
of any significant magnitude. Why?
Point mutations (base pair substitutions) of individual genes are
reversible and that alone indicates that such changes do not play
a significant role in evolution. By way of contrast, consider an
inversion. If such a change should occur, the probability of it
being reversed is virtually zero since the chromosome would have
to break in exactly the same two places in order for it to return
to its original configuration. A similar argument applies to the
improbable reversibility of chromosome fusion, dissociation or
reciprocal translocation. Furthermore these structural changes
are all-or-none events which have no intermediate states and cannot
possibly be regarded as gradual. Accordingly, one might anticipate
that these effects might be quite dramatic although unpredictable.
Incidentally, this perspective also offers an explanation for the
absence of transitional forms in the fossil record.
III-3. The first meiotic division
The ideal situation might be for an organism to simultaneously
reproduce its own genotype and produce trial balloons as well.
It is with this potentiality that a major significance of diploidy
becomes apparent. When a haploid creature undergoes a heritable
change it has lost its original genetic identity. That is not the
case for a diploid organism. To understand this important distinction
it is only necessary to realize that there are three self-replicating
elements involved. The first of these are the chromosomes, the second
are the centromeres and the third are the centrioles, the structures
at the ends of the spindles on which the chromosomes move. In mitosis
the centromeres and the chromosomes replicate in synchrony so that the
daughter chromosomes pass to opposite poles of the mitotic spindle.
The result is that the two daughter cells receive identical sets of
genes, becoming thereby clones of the original cell. In the first
meiotic division the centromeres do not duplicate when the chromosomes
do with the result that the two sister (identical) chromosomes
(dyads) must remain together during the first meiotic division.
This feature lies at the heart of the semi-meiotic hypothesis.
Figure 1. A diagram to illustrate the instantaneous formation of a
new chromosome pair following the occurrence of a single pericentric
inversion. O represents the centromere.
A. The original chromosome pair.
B. The inversion heterozygote.
C. The tetrad configuration prior to the first meiotic division.
D. The products of the first meiotic division following the
duplication of the centromeres.
From Davison (1984).
Consider an oocyte about to undergo meiosis. Assume further that
this oocyte has one chromosome which has undergone an inversion.
When the tetrad is formed at synapsis (Figure 1) it will consist
of two daughter chromosomes (sister strands or dyads) of original
structure and two daughter chromosomes each containing the inversion.
In the first meiotic division one pair of sister strands is discarded
into the first polar body leaving the other pair in the egg. If the
inverted pair is discarded, the oocyte retains the original genome.
If the normal pair is discarded the oocyte has instantly acquired
a new karyotype in homozygous form and, following the duplication of
the centromere (which results in the separation of the chromosomes)
an evolutionary potential as a new kind of diploid organism.
All genetic (evolutionary) changes originate in individual cells, in
individual chromosomes, in a particular organism. The evolutionary
significance of the individual will become apparent in a later
section. If the inversion in the above example occurred in a cell
destined to become part of the female reproductive lineage, then
at the termination of the first meiotic division, one half of the
products of that lineage will be like the original and one half will
be a potentially new kind of organism with a new paired (homozygous)
chromosomal genotype (karyotype) produced in a single cytogenetical
step. In this system the only requirement is for one or more oogonia
to be heterozygous. Such an evolving series would be expected to
produce a number of discrete products determined by the number of
chromosome rearrangements involved in the series. I do not suggest
that all new chromosome homozygotes would be new species. In fact
we know that is not necessarily so. Nevertheless, this perspective
is worthy of further attention.
III-4. Position effects and primate evolution
In Goldschmidt’s day the internal structure of chromosomes was not
well known and was limited in large extent to the giant salivary
chromosomes of the fruit fly Drosophila. New staining techniques
allow a much more detailed analysis of chromosome structure in many
life forms. Of special interest are the chromosomes of the order
Primates to which we belong. We are fortunate in having three close
relatives with which comparisons can be made: the chimpanzee, the
gorilla and the orangutan. The higher primates are also interesting
because they are among the most recent evolutionary products and
accordingly their karyotypes are likely to have retained their
original configurations.
Figure 2. Schematic representation of late-prophase chromosomes
(1000-band stage) of man, chimpanzee, gorilla and orangutan, arranged
from left to right, respectively, to better visualize homology between
the chromosomes of the great apes and the human complement.
From Yunis and Prakash (1982).
In 1982 Yunis and Prakash published a paper entitled “The Origin
of Man: A Chromosomal Pictorial Legacy”, in which the karyotypes of
man, chimpanzee, gorilla and orangutan are compared (Figure 2).
The karyotypes are remarkably similar providing convincing evidence
that we are all four related. The narrowed region of each chromosome
marks the position of the centromere, the structure to which the
spindle fibers attach during mitosis and meiosis. The differences
that can be recognized are largely structural rearrangements.
For example the three apes have 48 chromosomes while we have 46.
This has apparently resulted from the fusion of two of the ape
chromosomes to form a single human chromosome (chromosome 2).
Some of the differences consist of paracentric and pericentric
inversions of homologous chromosome segments as well as variations
in heterochromatin. As examples, chromosomes 4, 5, 9, and 12 of
man and chimpanzee each differ by a pericentric inversion. Certain
chromosomes exhibit reciprocal translocations. Other differences
include alterations in chromosome ends or telomeres as well as
variations in the position of nucleolar organizers (Yunis, J.J. &
Prakash, O. 1982). The original paper should be consulted for the
details.
The important point is that the differences which are evident
are precisely of the sort that Goldschmidt described: namely,
the restructuring of existing genetic information. Under close
examination of the karyotypes, the X chromosomes reveal very few
differences. This is exactly what one might expect if the four
species were linked gynogenetically. By way of contrast, the
male-determining (Y) chromosomes lack, both quantitatively and
qualitatively, the semblance one would expect had the four genera
evolved through sexual reproduction.
Also there are very small differences in both DNA and protein
composition between ourselves and our living relatives (Andrews 1987),
further supporting the view that conventional (point) mutations may
be of little or no significance in the evolutionary process.
IV. Sexual reproduction limits evolutionary change
All great truths begin as blasphemies.
— George Bernard Shaw
IV-1. The independent origins of sexual reproduction
In the Darwinian or sexual model, one might anticipate some universal
sex-determining mechanism operating throughout evolutionary history.
If, as I believe, the role of sexual reproduction is to limit
evolution, one would anticipate a wide variety of sex-determining
devices evolving independently. Such is the actual case. I found
that the idea of an independent sexual evolution had already been
expressed. The Russian cytologist N.N. Vorontsov was one of the first
to call attention to the independent evolution of sex determination.
Just as the transition from isogamy to anisogamy and to oogamy
took place independently of each other in the various phyla of
plants so the formation of mechanisms of the cytogenetical sex
determination with differentiated heterochromosomes follows
the same pattern in various kingdoms and phyla and results
in an independent occurrence of the XX-XY system in
Melandrium as well as in many Insects and Mammals,
whereas the ZW-ZZ system evolved independently in Trichoptera,
Lepidoptera, Serpentes and Aves. Against the background of
these facts it is unclear whether the male species of
different groups are homologous to each other or not;
they appear to be nonhomologous.
“The evolution of the sex chromosomes”
(1973), page 646
Notice the last sentence in which Vorontsov indicated that males
seem to be nonhomologous, a conclusion that would, by definition,
demand that they were independently produced and accordingly could
not be involved in a macroevolutionary continuum.
In addition to the devices mentioned by Vorontsov, other mechanisms
have also independently evolved. In the social insects the female
is diploid, the male haploid, a situation also found in rotifers.
In addition to these chromosomal mechanisms, the temperature during
sensitive developmental stages can serve to determine the sex as
in some turtles and crocodilians. Sex reversal occurs in certain
animals. Young oysters are male and transform into females when
they grow larger (protandry). This literature has been reviewed
by Bull (1983).
Not only are the cytological mechanisms of sex determination often
nonhomologous but the expression of the sexual phenotype may also
be nonhomologous. For example, both Drosophila and all mammals
have a heteromorphic (different form) XY male – XX female system.
However, sexual differentiation is mediated at the local cellular
level in Drosophila but by means of hormones in all mammals.
It is obvious that the two systems are in no sense related,
but must have evolved independently.
This is hardly the situation one would expect if sexual reproduction
were a requirement for evolutionary change. I think the most
reasonable explanation for this great diversity is that the
evolutionary steps involved in macroevolution were made prior to the
differentiation of obligatory sexual devices and, accordingly, must
have been gynogenetic (presexual) in nature, involving only the first
meiotic division. Viewed in this way the evolution of exclusively
sexual means of reproduction became the self-limiting step in the
evolutionary process. I regard this conclusion as inescapable
as I am unable to provide an alternative interpretation to these
undisputed facts.
IV-2. The importance of nonhomology
Treasure your exceptions.
— William Bateson
Irrationally held truths may be more harmful than
reasoned errors.
— T.H. Huxley
Homologous structures have a common origin. The same can be said
for homologous mechanisms. Any rational evolutionary hypothesis
must recognize, and incorporate into its fabric, nonhomology when
that becomes evident. Another example of nonhomology that correlates
favorably with the various sex-determining devices is the origin of
the definitive germ cells in contemporary vertebrates.
One of the hitherto most baffling features of vertebrate ontogeny
is offered by the origin of those cells (oogonia and spermatogonia)
destined to become the eggs and sperm. Again it is useful to place
evolutionary theory in historical perspective.
August Weismann (1891) is well known for having predicted meiosis and
for his interesting aphorisms such as: “The protozoa are immortal”
and “From eagle eggs come eagles”. Each of these statements implies
reproductive continuity which is, of course, required for any theory
of evolution. However, Weismann extended his hypothesis further with
his notion of the continuity of the germ plasm. According to this
concept there has been an unbroken chain of reproductive cells which
through modification have produced the many life forms that have
existed, a chain that exists to the present day. Evolution does
not demand a continuous cell lineage but only reproductive
continuity from one generation to the next.
The actual facts are as follows. In birds the cells destined to
become the germ cells first appear in the extra-embryonic endoderm
(germinal crescent) anterior to the head of the developing embryo.
Incidentally, this region has no homologue in the hatched bird as the
extra-embryonic endoderm is, by definition, resorbed as nutrient for
the developing chick. From there the presumptive germ cells enter
the circulatory system and, after a period of time in the bloodstream,
penetrate the walls of the venous circulation and invade the gonad
where they differentiate into the definitive gametes. In mammals
the presumptive germ cells first appear in the endoderm of the
allantois, a structure destined to become the urinary bladder of
the adult. From here they migrate in amoeboid fashion anteriorly
and laterally to reach the gonad where they complete their
differentiation. Thus, there is no way that the reproductive
cells of mammals can be homologized with those of birds as they
originate from opposite ends of the embryonic axis and reach the
gonads by completely different means.
Similarly, the eggs and sperm of the Anura (frogs and toads) arise
in an entirely different way than do those of the Urodela (salamanders
and newts). Staining methods reveal that in frogs, the cells destined
to become the germ cells result from the presence of preformed
granules near the vegetal pole of the unfertilized egg, a region
destined to become part of the endoderm. From there they move first
dorsally and then laterally to enter the embryonic gonads which are
mesodermal structures. In salamanders the presumptive germ cells
first appear in the mesoderm as a result of the inductive action of
the underlying endoderm on the lateral plate mesoderm. From there
they migrate medially to invade the embryonic gonads. Thus the germ
cells of the Anura and the Urodela do not even arise from the same
germ layer! In short, there is not a scintilla of evidence to support
the notion of germ cell continuity. The details of these differences
have been discussed elsewhere (Davison 1984). Also, the vertebrate
gonad is a sterile organ unable to produce germ cells from its own
epithelium (Nieuwkoop and Sutasurya 1979). Instead, the testis or
ovary receives its complement of eggs or sperm by a process of
invasion from extragonadal sources early in development. Since the
sources and modes of invasion are not homologous from group to group,
the continuity of the germ plasm is a myth. As someone so aptly put
it: “Hypotheses have to be reasonable — facts don’t.”
Note that these nonhomologies correlate favorably with the
nonhomologous devices that now serve to determine the sex differences.
In order to deal with all this, it is necessary to postulate that
contemporary reproductive cell lineages cannot be ancestral but have
independently replaced the original (semi-meiotic) lineage and that
the latter is no longer extant. We may never know the source of the
original cell lineage but a very reasonable guess might be the gonadal
epithelium, a tissue that has since become sterile. I can conceive of
no other way to cope with these realities.
IV-3. Semi-meiosis and the origin of diploidy
One of the most significant events in evolutionary history was the
transformation from haploidy to diploidy since, as I have indicated,
diploidy allows the retention of the original genome at the same time
that it permits new configurations to be produced as a result of the
first meiotic division. The transformation from haploidy to diploidy
has probably occurred many times. One such transformation bears
directly on the significance of the first meiotic division as an
evolutionary device.
In 1947, L.R. Cleveland published a short but highly significant paper
dealing with the origin and evolution of meiosis. Oddly enough, this
paper has gone virtually unnoticed. His material was the various
flagellate protozoa that live as commensals in the guts of wood-eating
insects. Of particular significance here are his observations on the
flagellate genus Spirotrichosoma which is found in three species of
Stolotermes, a primitive termite genus with species in Australia,
New Zealand and South Africa. The haploid number is 12 in
Spirotrichosoma and haploids are found in all three locales.
However, in addition, polyploids with 24, 48 and 60 chromosomes
are found only in the New Zealand populations. Clearly, we are
observing the evolution from haploidy to diploidy and polyploidy
in the New Zealand material. I quote Cleveland:
Nuclear division of these polyploids can be seen very
plainly, especially those with 4 rod-shaped chromosomes.
Every division is exactly alike: synapsis in the prophase,
followed by formation of tetrads, and movement of the
chromosomes to the poles as dyads, i.e. every division
is exactly like the first division in meiosis.
“The origin and evolution of meiosis”
(1947)
Following this single nuclear division the centromeres duplicate
allowing the sister chromosomes (dyads) to separate. The cycle
then repeats. Note that these animals have no sexual phase since
the second division never takes place. Accordingly, they present
a living example of the semi-meiotic mechanism. These observations
also suggest that the first meiotic division may be a more primitive
form of reproduction than diploid mitosis (Davison 1984 1993).
Another example of semi-meiosis is offered by the Beltsville strain of
small white turkey which produces a low but significant percentage of
its offspring parthenogenetically (Olsen 1965). The proof that the
mechanism is semi-meiotic is that all of these offspring are males.
In birds, it is the female that is heterogametic (ZW) while the male
is homogametic (ZZ). The Z chromosome is larger than the W
chromosome, just as the X chromosome is larger than the Y chromosome
in mammals. Prior to the first meiotic division the synaptic tetrad
consists of ZZ and WW dyads (sister strands). If, during the first
meiotic division, the ZZ dyad enters the polar body leaving the WW
dyad in the egg, the embryo fails to complete development. (WW is
apparently lethal in birds.) If the WW dyad passes into the polar
body and the ZZ dyad remains in the egg, it must develop as a male
which is the actual case. This example also serves to demonstrate
the instantaneous production of a chromosome homozygote from a single
heterozygous source. If birds, like mammals, had homogametic females,
the parthenogenetic turkey, in theory at least, would be capable of
progressive evolution at the same time that it could retain its
original genetic (species) constitution!
There is another curious fact that lends credence to the semi-meiotic
hypothesis. Since spermatozoa are universally haploid in their
functional state, one might anticipate that the same would be true for
the mature ovum. Such is not the case. The vast majority of animal
eggs are unreduced at the time the sperm enters. The egg at this time
has often produced the first polar body and is arrested in metaphase
of the second meiotic division and so is still diploid as it
has completed only the first meiotic division. This is the
case for most, if not all, vertebrates including Homo sapiens.
I have suggested that this might represent an evolutionary relic
from a time when the sperm either was not necessary for activation or
served only as an activator without contributing genetic information
(Davison 1984). Such a reproductive mode would be, by definition,
semi-meiotic. In any event, some agency other than the sperm serves
to activate the egg of the parthenogenetic turkey.
IV-5. Sex reversal in birds and amphibians
It is obvious for cytogenetic reasons why only male turkeys can be
produced by means of the first meiotic division. Birds demonstrate
another important feature of sex differentiation. It has been known
since antiquity that hen chickens occasionally transform into crowing
roosters. In birds, while both testes are present in the male,
females have only a single ovary, the left one. If the ovary is
destroyed by disease or is surgically removed, the other potential
gonad is relieved of inhibition (derepressed) and can then develop
into a testis. This is possible because of the bipotential nature of
the vertebrate gonad. Like the kidney and adrenal gland with which
it is developmentally associated, the embryonic gonad consists of an
outer cortex and an inner medulla. Normally, the genotype determines
which of these will develop. The cortex becomes the ovary and the
medulla the testis. Each functional gonad serves to inhibit the
development of the other (Witschi 1956).
The bipotential nature of the vertebrate gonad is also demonstrated
by observations on the development of frogs. Frogs (Rana species),
while they lack heteromorphic (visibly different) sex chromosomes,
can be shown to have heterogametic (XY) males like humans by rearing
the tadpoles in the presence of small amounts of male hormone
(methyltestosterone). The male hormone overrides the genetic
constitution so that all of the animals, both XY and XX, develop into
fertile males. When the XX males are crossed with XX (normal) females
they produce mostly, but not exclusively daughters, demonstrating that
even in sexual reproduction the female genome is capable of producing
both sexes. Similarly, genetic males may be transformed into females
by rearing the larvae in the presence of female (estradiol) hormone
(Witschi 1956).
Normally, the sex of frogs is determined at the moment the sperm
enters the egg which, in nature, is instantly as the eggs are
extruded into the pond water which is already charged with sperm
released by the male partner. Early in this century Richard Hertwig
discovered that, if fertilization is delayed, an excessive number of
males are produced, again demonstrating the bipotentiality of the
gonad (Wilson 1925).
In 1916, Jacques Loeb induced several thousand frog eggs to divide
by pricking them with a fine needle. The vast majority of the
embryos proved to be haploid and never completed larval development,
but twenty were successfully raised to maturity and were shown to
be diploid, undoubtedly due either to the occasional failure of the
second meiotic division to take place or to the reentry into the egg
of the second polar body nucleus (Wilson 1925). Thus these frogs were
produced semi-meiotically. Of the 20 frogs, 15 were males, 3 were
females and 2 were of uncertain sex. The preponderance of males is to
be expected in light of Hertwig’s observations on delayed activation.
More recently, large numbers of gynogenetic frogs have been produced
by utilizing sperm irradiated with ultraviolet light. These sperm
serve to activate the egg to complete meiosis and proceed with
development but the sperm contribute no genetic information.
Following activation the eggs are heated briefly which serves to
suppress the second meiotic division. This procedure produces large
numbers of gynogenetic normal diploid frogs. Thus these animals are
examples of experimentally induced semi-meiosis. As with Loeb’s
experiments these are not all female with about 3.5 females to each
male. These males remain, of course, genetically female (XX) and,
when crossed with normal (XX) females, produce primarily but not
exclusively daughters. As with hormonally sex-reversed (XX) males,
approximately one in twenty of their progeny is a male (Nace and
Richards 1969). These findings are significant because they
demonstrate convincingly that all of the necessary genetic information
for both sexes is contained in the female genome. It is significant
that transformed (XX) male frogs are fertile, and the fertility
is independent of the means by which they were produced, whether
by hormonal transformation, experimental gynogenesis or delayed
fertilization. The last two means probably have the same temporal
basis involving delayed activation.
The capacity of the female genome to produce both sexes is not
limited to the vertebrates since it is also demonstrable in the
social insects, water fleas (Cladocera) and rotifers just to mention
a few of many invertebrate examples. The same capacity is obvious
in all monoecious (hermaphroditic) organisms, examples of which occur
throughout both the animal and plant kingdoms.
IV-6. Semi-meiosis and genetic variability
The gynogenetic offspring from a common mother are also interesting
from the point of view of semi-meiosis as a device for generating
genetic diversity. Frogs, like mammals, have evolved immune systems
and will reject a skin transplant from a genetically different donor.
Gynogenetically produced siblings reject skin transplants from one
another. They also reject skin transplants from their common mother
because none of them have all of her genes. In fact they each have
exactly one half (qualitatively) of her total genetic constitution,
the other half having been eliminated in the first polar body.
The mother will, however, accept a skin transplant from any of
her gynogenetic progeny because none of them have any genes that
are not hers (Nace and Richards 1969).
There are two sources of the genetic diversity generated by
semi-meiosis. The first is the random segregation of maternal and
paternal dyads (sister strands) that has taken place as a result of
the first meiotic division. Frogs (Rana) have 13 pairs of
chromosomes. Accordingly there are 2 raised to the 13th power or
8192 possible combinations. For humans, with 23 pairs of chromosomes,
the number of combinations becomes 8,388,608. The second source of
variation is due to crossing-over (exchange of chromosome segments
between non-sister strands) which has preceded the first meiotic
division. Thus the genetic diversity generated during the first
meiotic division is, for all practical purposes, limitless.
While it is true that semi-meiosis can produce new structural
chromosome pairs (homozygotes), it is not true that it necessarily
leads to gene homozygosity. In sexual (Mendelian) reproduction, in
the absence of selection, heterozygosity can never exceed 50% even if
one starts with 100%, as in crossing two heterozygotes, since it is
immediately reduced to 50%. This limitation does not apply to the
first meiotic division. Through experimental gynogenesis one can
detect heterozygosity by employing heterozygous females and then
inhibiting the second meiotic division. Lindsley et al (1956) found
cross-over (heterozygote) frequencies of 0.688, 0.694 and 0.724 for
three characters in the axolotl (a urodele amphibian) and Davison
(1961) found a frequency of 0.78 for the Burnsi locus in the frog
Rana pipiens. The only requirement for this result is that the genes
be at an appropriate distance from the centromere which apparently
is the case for these four genetic loci. Accordingly, for some genes
at least, heterozygosity can substantially exceed that possible by
means of sexual reproduction. By this I do not mean to imply that
heterozygosity necessarily confers some adaptive advantage as I am
not at all certain that is the case.
V. The failure of the Darwinian hypothesis
Let us give nature a chance; she knows her business better than we do.
— Montaigne
Nothing is more damaging to a new truth than an old error.
— Goethe
Since the Darwinians have chosen to ignore the semi-meiotic
hypothesis, I will introduce what I must imagine their objections
might be and then comment on the evidence for that perspective.
The Darwinian or sexual model has restraints that are necessary for it
to succeed. The achievement of both gene and chromosome homozygosity
require that the genetic alterations occur in small isolated
populations. This is necessary because the probability of two
heterozygotes mating would be very small in a large population.
Incidentally, the semi-meiotic model has no such restraint. The
Darwinians might simply say that the sexual model could also produce
chromosome and gene homozygosity through the inbreeding associated
with small or insular populations. It is precisely here that their
hypothesis fails. For example, the biota of the Galapagos Islands
closely resembles that of neighboring Ecuador. Darwin’s celebrated
finches have all been placed in the genus (or subgenus)
Geospiza. Since they are all extremely similar, it is not
surprising to learn that they produce spontaneous fertile
and genetically fit hybrids (Grant and Grant 1994). Thus, by a
physiological criterion they are one species and, as with dogs
and goldfish, no significant evolution has really taken place.
They too reproduce sexually.
There is another difficulty with the sexual model when one considers
chromosome restructuring. Consider a chromosome pair heterozygous
for a paracentric inversion. A single cross-over within the inversion
loop will lead to the formation of an acentric and a dicentric
chromosome, while the same kind of cross-over occurring in a
pericentric inversion heterozygote leads to two monocentric
chromosomes each carrying a deficiency and a duplication. All such
gametes can be expected to result in a lethal zygote (White 1973).
In short, chromosome restructuring is simply not compatible with
sexual reproduction. In fact, sexual reproduction tends to prevent
rather than promote chromosome restructuring as chromosome
restructuring leads to a lower reproductive efficiency due to the
deleterious effects of crossing-over prior to the first meiotic
division. Note that in the semi-meiotic model the new chromosome
homozygote need only be produced once since the capacity to
gynogenetically generate both sexes has been clearly demonstrated in
the material already described and may have been a common feature of
macroevolution in the past. Once the new chromosome homozygote has
been produced the deleterious effects of crossing-over immediately
disappear and only re-manifest when one member of the new chromosome
pair undergoes a further structural change.
V-2. The evidence from cytogenetics
The great tragedy of Science — the slaying of a beautiful
hypothesis by an ugly fact.
— T.H. Huxley
I fail to understand why Huxley would have considered such a
revelation as tragic. Facts and facts alone remain the basis
for all true progress and accordingly they can only be beautiful
– never ugly! Stated another way — How can a hypothesis be
regarded as beautiful when it does not conform with the facts?
Any hypothesis of organic evolution must stand in accord with
the realities of cytogenetics. What is critically relevant to
the argument presented here is a simple question: Were chromosome
restructurings effected sexually, as the Darwinian view demands, or
were they produced by some other means? The Australian cytologist
Michael J.D. White had a number of very pertinent remarks to make
on this issue. Here are several which go directly to the very heart
of the matter:
The conclusion we must draw from these facts (and a great many
more instances of the same kind in beetles, mammals and in
fact in almost every group of animals whose chromosomes have
been studied) is that, in certain groups at any rate, fusions
and dissociations which exist as cytotaxonomic differences
between species have not been preceded by a condition of
balanced polymorphism in an ancestral population.
(my emphasis)
Animal Cytology and Evolution
(1973), page 765
It seems safe to predict that any discussion of the broad
mechanisms of evolution in, say, twenty-five years’ time,
will have to take far more account of the chromosomes
themselves as bodies composed of nucleic acid and proteins,
and their relations to the rest of the cell at various stages
of mitosis and meiosis. And, as indicated earlier, it will
almost certainly lay more stress on the role of chromosomal
rearrangements in initiating and promoting speciation.
(my emphasis)
Ibid., page 783
Referring to the many chromosomal rearrangements that have occurred
in the evolution of the species in the genus Drosophila, White
offered the following comment.
The evidence in favor of the view that many cytotaxonomic
differences have arisen without passing through an adaptive
polymorphism stage has been growing steadily. Even in
Drosophila the fifty-eight fusions have most likely
established themselves without benefit of heterosis.
(my emphasis)
Ibid., page 768
White’s language is unmistakable. He has surmised that the
chromosome restructurings were, in all likelihood, not produced
sexually. Once again we witness the complete failure of the
Darwinian model. I submit that if they were not produced sexually,
there remains only one other conceivable way they could have been
produced and that is semi-meiotically as I have indicated. If there
is another way, I can only hope that someone will enlighten me!
I realize that the vast cytogenetic literature is beyond the scope
of this essay. Accordingly, in light of the above, I place the burden
of proof on the Darwinians by challenging them to present karyotypic,
genetic, taxonomic, fossil, or any other kind of evidence indicating
that true species, genera, families, or any of the higher taxonomic
categories have ever been produced or can now be produced through
the agency of sexual reproduction. I, in general agreement with
White, can find nothing in support of that proposition.
V-3. A hypothetical reconstruction of evolutionary history
The following is an attempt to explain the course of evolution
while incorporating all of the preceding verified facts.
Any hypothesis that fails to account for all of the facts
is fundamentally flawed and must be considered invalid.
It is only necessary to accept the reality that contemporary germ
cells cannot be ancestral but must be secondary in origin. It follows
that there must have been times when organisms possessed two sources
for reproduction, the semi-meiotic lineage which I have described
and the sexual lineage which now largely prevails. It is reasonable
under those conditions that both modes of reproduction could occur
simultaneously. Why then has the original or semi-meiotic lineage
largely disappeared? First, while the semi-meiotic mode is ideal for
the production of new trial balloons, that could become a disadvantage
once a new and successful creature has been produced. Second, sexual
reproduction has a potential advantage in its capacity to produce
limited variation within a narrow range. The sexual mode could thus
be useful in adapting the organism to minor environmental changes.
Thus, the sexual lineage might be expected to replace the semi-meiotic
lineage in a changing environment. However, severe changes might
be beyond the capacity of the sexual mode, leading to extinction.
This would seem to be the situation at present when so many species
are disappearing.
The vast majority of all organisms that have evolved have become
extinct. Why? I answer that it may be due, at least in part, to the
fact that sexual reproduction is not well suited to the elimination
of genetic defects. Nearly all point mutations are deleterious if
not lethal; in the sexual mode, they tend to accumulate, leading
ultimately to the extinction of the forms in question. Particularly
vulnerable are animals that reproduce infrequently, thereby presenting
few opportunities for natural selection to cull the genetic
defectives. Giant animals, which typically leave few offspring,
have been especially prone to extinction, while their smaller and
more prolific cousins have survived. In further support of this
view, many “living fossils” — primitive-looking creatures with
extraordinary evolutionary longevity — produce enormous numbers of
progeny, ensuring that some will be genetically fit; they also tend to
live in the oceans, which are more stable than either the freshwater
or terrestrial environments. The bivalve Ostrea serves as an example
of both strategies, the coelacanth an example of the latter.
Obversely, semi-meiosis is admirably suited to the elimination
of deleterious genes and gene arrangements since these tend to be
exposed as homozygotes. Accordingly, the semi-meiotic lineage could
theoretically continue to purge itself of defective genes and gene
arrangements as long as it remained in operation (Davison 1993).
In support of this interpretation it is interesting to note that newly
evolved life forms typically flourish for some time before ultimately
declining and becoming extinct (Schindewolf 1993). Life forms that
were produced semi-meiotically would, at their inception, be expected
to be relatively free of defective genes and gene arrangements since
these would have been eliminated as soon as they were expressed and
thereby exposed in homozygous form.
VI. Gradualism versus saltationism
Species and the higher categories originate in single
macroevolutionary steps as completely new genetic systems.
— Richard B. Goldschmidt
As mutation always involves leaps or interruptions,
we can understand why species, in our sense of the word,
should be sharply distinguished one from another.
— Leo S. Berg
Once again we observe virtually identical conclusions drawn,
as far as I can determine, independently, this time by Richard
Goldschmidt and Leo Berg.
Darwinism rests firmly on gradualism and therein resides another
of its failures. The fossil record simply fails to support this
notion. The semi-meiotic hypothesis, depending as it does on
chromosome restructuring, represents the antithesis of gradualism
and finds much in the fossil record in accord with its implications.
The record often discloses the sudden appearance of new kinds of
living things. For that reason I think it is more meaningful
to emphasize the sudden appearance of a new kind (Genus or higher
category) of organism than it is to engage in endless speculation
about what constitutes a species. Virtually all the evidence supports
Goldschmidt’s view that subspecies are “blind alleys” which are in no
way involved in the process of macroevolution, a conclusion reached by
Burbank, Bateson and Petrunkevitch as well. The four higher primates,
man (Homo), Chimpanzee (Pan), Gorilla (Gorilla), and Orangutan (Pongo)
are all in separate genera. How can they be gradually transformed
one into the other when the very differences which they so strikingly
exhibit (chromosome reorganizations) by definition have no conceivably
gradual or intermediate states? The restructuring of a chromosome,
like pregnancy, is an all-or-none event!
It is the discrete nature of species that allows an amateur
bird-watcher like myself to identify every bird I see with a
simple key or even a picture. It is obvious from the absence of
intermediate forms that a primary role for natural selection is
to prevent variation and accordingly to maintain the status quo,
a conclusion reached by Punnett long ago as was indicated earlier.
On the other hand, the semi-meiotic hypothesis remains in complete
accord with evolutionary saltation (from the Latin saltus, to leap).
Richard Goldschmidt, Leo Berg and Otto Schindewolf all favored
saltation as an evolutionary device. This is highly significant
because they approached evolution from completely separate
directions: genetics, zoogeography and paleontology respectively.
Of paramount importance is the agreement that has been reached by
Schindewolf and Goldschmidt especially since each drew his conclusions
independently. It is dramatically demonstrated in the following
excerpt from Schindewolf’s Basic Questions In Paleontology
(German edition 1950, English translation 1993), page 352:
Richard Goldschmidt laid out his intellectual edifice in
1940 in an extensive, thoroughly provocative work entitled
The Material Basis Of Evolution, with which I was not
yet familiar when I prepared this manuscript. His earlier
communications on this subject have had considerable influence
on my thinking or have strengthened it, but in essence,
the concepts described here grew out of my own analysis
of paleontological material. All the more surprising
and pleasing, then, is the broad agreement in our views.
“Schindewolf’s theory is practically identical with that of
Goldschmidt,” as D.D. Davis (1949) observed recently based
on my 1936 publication. I regard this convergence of views
arising from extremely different premises as a welcome sign
that we are on the right track.
Indeed, Goldschmidt goes further than I and is in a position
to support his phylogenetic conclusions genetically. He holds
that microevolution through the accumulation of micromutations
is a process that, in adaptation to the environment, leads
only to a diversification within the framework of species
and does not exceed the boundaries of species. “Subspecies,
therefore, are actually neither incipient species nor models
for the origin of species. They are more or less diversified
blind alleys within the species.” According to him,
macroevolution would require a different evolutionary
mechanism, one that would create the decisive transformational
step from species to species, from one higher category
into another. It would not take place through a series
of atomistic alterations but by way of a far-reaching
transformation of intrachromosomal structures. This
repatterning, or Systemmutation, is attributable to
cytologically provable breaks in the chromosomes, which
evoke inversions, duplications, and translocations. A single
modification of an embryonic character produced in this way
would then regulate a whole series of related ontogenetic
processes, leading to a completely new developmental type.
Accordingly, gross anatomical differences between two
taxonomic types would not have to evolve through the
simultaneous selection of numerous small mutants as
determiners for each individual organ but could arise
through a single evolutionary step.
This explanatory attempt by Goldschmidt has aroused much
opposition among other geneticists. Paleontology has no right
to intervene in this dispute. From my personal point of view,
I can add only that Goldschmidt’s inferences completely meet
the challenge that fossil material appears to me to pose, and
that he, as a leading geneticist, has presented a complete
interpretation that does justice to the tangible, historical
phylogenetic data.
Ten years earlier, Goldschmidt had commented on Schindewolf in
The Material Basis of Evolution (1940), page 395:
… I need only quote Schindewolf (1936), the most
progressive investigator known to me, who showed that the
material presented by paleontology leads to exactly the same
conclusions as derived in my writings, to which he refers.
He elaborates the thesis that macroevolution on a higher
level takes place in an explosive way within a short
geological time, followed by a slower series of orthogenetic
perfections, as exemplified in the oft-quoted evolutionary
series. He realizes that the conception of preadaptation
accounts completely for this type of evolution. He shows
by examples from fossil material that the major evolutionary
advances must have taken place in single large steps, which
affected early embryonic stages with the automatic consequence
of reconstruction of all the later phases of development.
He shows that the many missing links in the paleontological
record are sought for in vain because they never existed:
“The first bird hatched from a reptilian egg.”
Schindewolf and a few others also realize that the genetical
and phenogenetical facts and ideas from which my thesis was
derived furnish the basis for an understanding of such a
process of evolution. Thus we see that the results of
paleontology — see Schindewolf for references to other
authors who have come to similar conclusions — vindicate
the thesis which we developed here. It is gratifying that all
the disciplines which furnish material for the understanding
of evolution — taxonomy and morphology, descriptive and
experimental embryology, static and dynamic (physiological)
genetics, comparative anatomy and paleontology — supply ample
and parallel evidence for a theory of evolution which is more
plausible than the neo-Darwinian theory.
These excerpts constitute powerful support for saltation as the
key macroevolutionary device, and accordingly lend further credence
to the semi-meiotic hypothesis.
Leo Berg offered very similar conclusions in a series of 10
comparisons he made between Darwinism and Nomogenesis (evolution
according to law) at the very end of his book. Numbers 3, 5, 7
and 8 are in complete accord with what has so far been presented
here. In each instance the Darwinian view is presented first,
followed by Berg’s view.
3. Based on chance variations — based upon laws.
5. By means of slow, scarcely perceptible, continuous
variations. — By leaps, paroxysms, mutations.
7. The struggle for existence and natural selection are
progressive agencies. — The struggle for existence and
natural selection are not progressive agencies, but being,
on the contrary, conservative, maintain the standard.
8. Species arising through divergence are connected by
transitions. — Species arising through mutations are
sharply distinguished one from another.
I cannot resist commenting on the quotation that Berg ascribed to
T.H. Huxley in the frontispiece to his book: “Science commits suicide
when she adopts a creed.” That has proven to be a remarkably slow
form of suicide in the case of Darwinism, which made its debut in
1859 and is still apparently thriving in the twenty-first century!
VI-2. The significance of the individual in macroevolution
The definition of the individual was: a multitude of one million
divided by one million.
— Arthur Koestler
The history of science is science itself; the history of the
individual, the individual.
— Goethe
Semi-meiosis, being a gynogenetic process, can have enormous impact
as a result of a single occurrence since the unique genome can produce
an unlimited number of products including, at least in those forms
for which we have good information, members of the opposite sex.
The Darwinians place great emphasis on populations as the units of
evolution. There is absolutely no rationale for this perspective.
As was indicated earlier, all genetic (evolutionary) changes originate
in individual chromosomes in individual germinal cells in individual
organisms. If a newly evolved creature is able to reproduce itself,
it will do so and the numbers of that species will increase. It is as
simple as that. Accordingly, population genetics has a questionable
place in the evolutionary process.
While the Darwinians have emphasized populations, the significance of
the individual was certainly obvious to Robert Broom. From his 1933
book, The Coming of Man in which he is discussing the origin
of the mammals (page 215, my emphasis):
A line of small generalized Therocephalians appears to have
been successful. They gave rise to a higher group, the
Bauriamorphs, and some member of this group gave rise
to the Ictidosaurians; and from an Ictidosaurian arose
the first mammal. The little line that ran from the
Therocephalians to the first mammals was entirely made up
of small animals. Many side branches specialized and became
moderately large, but these all soon perished. Only the
little generalized types carried on the line, but they always
died out as soon as a higher type arose. Probably only one
Bauriamorph led to the Ictidosaurians, and almost certainly
only one Ictidosaurian gave birth to the mammalian stem.
Apparently in Upper Triassic times a small Ictidosaurian
— perhaps as small as a mouse — developed hair, and about
the same time the lower jaw formed a new joint between the
dentary and the squamosal bones, and the little bones of the
jaw became ear ossicles, and the heart became four chambered.
All these changes probably took place nearly simultaneously.
We might regard the evolution of one of these characters as a
happy accident, but that all should arise about the same time
and by accident is incredible.
Broom correctly understands that it is the individual which is the
unit of evolutionary change.
Figure 3. Diagram showing how the reptilian lower jaw (a)
was refashioned into the mammalian lower jaw (b).
De = dental; Spl = splenial; Ang = angular; Sang = supraangular;
Art = articular; Pmx = premaxillary; Mx = maxillary; Jug = jugal;
Squ = squamosum; Qu = quadratum; Ty = tympanicum; Mall = malleus;
Inc = incus.
From Schindewolf, Basic Questions in Paleontology (1993), page 211.
It is revealing to compare Broom’s treatment of the origin
of the ear ossicles (malleus or hammer, incus or anvil and
stapes or stirrup) with the independent and virtually
identical conclusions of Schindewolf:
The vertebrate lower jaw, for example, is composed either
of several separate parts and joined to the skull by the
auricular, as in reptiles [Figure 3a], or — as in mammals –
consists of a single bony element, the dentary, which takes
on the function of articulation with the skull [Figure 3b].
Slow, smooth transitions between these qualitatively opposing
structures taking place during postembryonic developmental
stages, when the jaw mechanism must be able to function,
are inconceivable.
To be sure, we recognize in the reptilian lineages that
lead to mammals a gradual, quantitative reduction of the
articular and of the other individual bones of the lower jaw,
paving the way for the transformation and bringing the two
types closer together. However, the fundamentally decisive,
final step — the complete disappearance of these bones
or their transformation into elements of the auditory
area — must have taken place discontinuously, suddenly,
between one individual and the next, during an embryonic
developmental stage.
(Schindewolf’s emphasis)
Basic Questions in Paleontology
(1993), pages 211-212
This concurrence is extraordinary since neither Schindewolf nor Broom
makes any mention of the other which is not surprising considering the
language differences. Thus, just as Schindewolf, Berg and Goldschmidt
have independently identified saltation as the mechanism for
macroevolution, so Schindewolf and Broom have independently, and
in my view correctly, identified the individual as the instrument
of evolutionary change. Both of these conclusions are, of course,
incompatible with neo-Darwinian theory. It is equally obvious that
the individual cannot practice sex, since that act requires two.
If not sex, there is left only one conceivable alternative and
that is the first meiotic division as I have proposed. Again,
the conclusion is inescapable.
Since it is the individual that is responsible for evolutionary
progress, the rare event can assume enormous significance,
a consideration that should be kept in mind when asking the
question — Is evolution finished? Perhaps it is not!
Therefore evolution follows a determined direction.
— Leo S. Berg
The existence of oriented lines is a fact, and not a theoretical
view; a line can only be identified and exists solely because it
embodies a given trend appearing in individuals which derive from
one another and succeed one another in time.
— Pierre Grassé
VII-1. Are there laws governing evolution?
The above two quotations once again demonstrate the independence with
which two eminent scientists, one Russian and one French, and each
seemingly oblivious to the views of the other, have reached identical
conclusions about the nature of evolutionary sequences. Could this be
a simple coincidence and are they both wrong? I do not hesitate to
answer no to both questions.
I have already mentioned the Law of the Reversion to the Average
discussed by Burbank. This would seem to be an anti-evolutionary
law since it returns the variants to the original wild type.
It is clearly demonstrated by the role natural selection plays when
domesticated animals are returned to the wild. The aberrant selected
forms rapidly disappear in favor of the more conservative types which
come to resemble their more distant ancestors.
Leo Berg (1969), as the complete title of his book suggests,
believed that all of both ontogeny and phylogeny is determined
by law, a conclusion which seems to be shared not only by Pierre
Grassé but also by Robert Broom (1933). Since they are all
three evolutionary biologists for whom I have enormous respect, far
be it from me to challenge their convictions, especially since logic
has compelled me (admittedly reluctantly) to that same realization
myself. I am simply unable to offer any other interpretation.
Figure 4. Phyletic size increase in the horse.
From bottom to top:
Eohippus. Lower Eocene.
Orohippus. Middle Eocene.
Mesohippus. Oligocene.
Merychippus. Miocene.
Pliohippus. Pliocene.
Equus. Recent.
(After R.S. Lull, redrawn.)
From Schindewolf, Basic Questions in Paleontology (1993), page 292.
Figure 5. Reconstruction of a number of stages in the phylogeny
of the titanotheres showing a progressive increase in body size.
(After H.F. Osborn 1929.)
From Schindewolf, Basic Questions in Paleontology (1993), page 291.
Figure 6. Phyletic size increase in cephalopods. a shows a
very schematic Ordovician Endoceras; in contrast, the oldest
representative of the Nautiloidea (Plectronoceras), shown at the same
scale, is represented by the size of the dot above the letter b and
even exaggerated at that. c gives an idea of the size of the giant
ammonite Pachydiscus, from the Upper Cretaceous of Westphalia,
compared to the average size of the oldest Devonian ammonoids,
the dot above d.
From Schindewolf, Basic Questions in Paleontology (1993), page 298.
Figure 7. Aberrant shell types of Upper Triassic and Cretaceous
ammonoids showing the dissolution of form within a stock facing
extinction, in some instances with broad similarities of form.
a. Choristoceras. b. Rhabdoceras. c. Cochloceras. d. Ammonitoceras.
e. Baculites. f. Turrilites. g. Ancyloceras. h. Hamulina.
i. Heteroceras. k. Scaphites. l. Hyphantoceras. m. Nipponites.
(After Janensch, d’Orbigny, Roman, von Zittel, and others.)
From Schindewolf, Basic Questions in Paleontology (1993), page 142.
There are certain phenomena associated with evolution which, while
they might not be described as laws, do characterize much of the
fossil record. One of these is orthogenesis or evolution in a
definite direction. It is demonstrated with clarity in the evolution
of the horse (Figure 4) where increase in size and reduction in digits
proceed simultaneously. Another, apparently universal feature of
orthogenesis is that new life forms typically appear as small
organisms which subsequently become larger and more specialized.
This tendency is obvious in dinosaurs, titanotheres (Figure 5) and
ammonites (Figure 6) and has been discussed at length by Schindewolf
(1993, page 193). He identified three phases in the evolutionary
process which he regarded as having been episodic and cyclic in
nature. The first phase which involves the rapid establishment of new
forms he termed typogenesis. The slower second phase of elaboration
and diversification he called typostasis. The third phase, typolysis,
is characterized by gigantism and overspecialization often coupled
with bizarre morphological developments (Figure 7). This phase ends
with extinction. The reality of these phases is well documented but
the causes remain obscure.
Another common phenomenon is that of convergence. For example,
the similarities between the marsupial wolves and bears and their
placental counterparts defy any mechanism based upon the accidental
production of virtually identical morphologies in unrelated animals.
I present an alternative explanation for what has been called
convergence in a later section.
VII-2. Epigenesis and preformation
Evolution is in a great measure an unfolding of preexisting
rudiments.
— Leo S. Berg
The existence of internal factors affecting evolution has to be
accepted by any objective mind.
— Pierre Grassé
Once again Berg and Grassé independently have concurred on another
critical point which cannot be accommodated within the Darwinian
hypothesis, since the Darwinians deny the existence of such
endogenous factors.
The terms epigenesis and preformation originated from the study
of embryonic development. Epigenesis refers to the necessity
for embryonic stages to occur in a definite sequence. Thus the
formation of the nervous system (neurulation} cannot occur until
after the formation of the primitive digestive system (gastrulation).
Therefore development is primarily, although not exclusively,
epigenetic in nature. These ontogenetic phenomena have interesting
counterparts in phylogeny (evolution).
First, with respect to preformation, this concept is clearly favored
by what we know about position effects. It is largely the same genes
which produce a new species when they are rearranged, as is so evident
in the primate karyotypes previously discussed. All living things are
very similar at the molecular level using virtually identical enzyme
systems for the extraction and utilization of energy. The energetic
currency (adenosine triphosphate) is universal in both the plant and
animal kingdoms as well as in the prokaryotes. At the structural
level, the nine plus two arrangement of microtubules is universally
the same in all cilia and flagella wherever they are found in the
living world. Thus the infinite variety of living creatures can be
compared with the variety of combinations that can be obtained from a
deck of playing cards in which it is only the arrangement and sequence
that are of consequence. The cards (genes) remain the same.
Figure 8. Diplodinium ecaudatum.
From Sharp (1914).
ABBREVIATIONS
ador. m. — adoral membranelles.
an. — anus.
ant. cil. r. — anterior ciliary roots.
ant. c. v. — anterior contractile vacuole.
bd. l. — boundary layer (ectoplasmic).
cir. osa. r. — circumoesophageal ring.
caoc. — caocum.
cut. — cuticle.
c. v. r. — region about contractile vacuole.
D. — dorsal side of body.
d. disk — dorsal disk.
d. fur. — dorsal furrow.
d. m. str. — dorsal motor strand.
d. m. — dorsal membranelles.
ect. — ectoplasm.
ent. — entoplasm.
fd. vac. — food vacuoles.
i. ador. lip — inner adoral lip.
i. d. lip — inner dorsal lip.
L. — left side of body.
l. sk. a. — left skeletal area.
mac. — macronucleus.
mic. — micronucleus.
m. m. — motor mass (motorium).
o. ador. fur. — outer adoral furrow.
o. ador. lip — outer adoral lip.
o. d. fur. — outer dorsal furrow.
o. d. lip — outer dorsal lip.
oes. — oesophagus or cytopharynx.
oes. f. — oesophageal fibers.
oes. retr. str. — oesophageal rectrator strands.
op. — operculum.
op. f. — opercular fibers.
or. — oral opening, mouth, or cytostome.
or. cil. — oral cilia.
or. disk — oral disk.
post. cil. r. — posterior ciliary roots.
post. c. v. — posterior contractile vacuole.
R. — right side of body.
rect. — rectum.
rect. f. — rectal fibers.
r. sk. a. — right skeletal area.
sk. lam. — skeletal laminae.
susp. f. — suspensory fibers.
V. — ventral side of body.
v. and r. sk. lam. — ventral and right skeletal laminae.
v. sk. a. — ventral skeletal area.
n. m. — nuclear membrane.
A remarkable example demonstrating preformation is presented by
the ciliate protozoan Diplodinium (Epidinium) ecaudatum(Figure 8 )
which exists in huge numbers as symbionts in the stomachs of
cattle. This tiny creature has a kind of “brain” (motorium)
with circumoesophageal “nerve” connectives resembling those of
annelids and arthropods, “muscles” (myonemes), a kind of segmental
“spinal column” (skeletal laminae), a “mouth”, “esophagus”, “rectum”
and “anus” (cytopyge), all elaborated within the confines of a single
cell (Sharp 1914). Such an animal not only proves that all the
necessary information is already present for these structures at the
protozoan level, but at the same time it serves to cast serious doubt
on the notion that multicellularity is a necessary prerequisite for
the division of labor. Why this creature should have such an array
of advanced features remains a complete mystery. Could it be there
to provide us with a clue concerning the nature of the evolutionary
process? I like to think so!
Another example is provided by the precocious evolution of the
placenta in animals as primitive as certain sharks. Leo Berg
(1969) discussed these and related phenomena at some length to
provide examples of what he called physiological acceleration,
an interpretation in obvious accord with the preformation concept.
More recently, the discovery of the homeobox gene complex has
led to its identification in a great variety of living creatures.
This too can be taken to support the notion that much of the necessary
information for subsequent evolution is present very early with only a
fraction of it being expressed in the evolution of a particular life
form. A comparable phenomenon is apparent during ontogeny in which
each cell in the body may contain all the information for the
synthesis of every protein but only a small fraction of that
information is expressed in a particular cell type, as for example,
the synthesis of hemoglobin only in erythroblasts or pepsinogen only
in certain cells of the stomach lining.
The very word evolution is derived from the Latin evolvo, meaning
to unfold, as the pages of a book, thereby indicating that the
information is already present (preformed).
On the other hand, epigenesis may be demonstrated in many
evolutionary sequences. For example, with the evolutionary
replacement of cartilage with bone, aquatic vertebrates acquired
a density greater than that of water and would have been relegated to
the bottom were it not for the invention of the swim bladder, a hollow
outgrowth of the embryonic digestive system. This hydrostatic organ
is homologous with the lung which, of course in turn, made the
invasion of land possible and ultimately the evolution of the higher
vertebrate taxa (amphibians, reptiles, birds and mammals). On the
other hand, the continuing success of the Chondrichthyes (sharks,
skates, rays and chimeras) may reside in their having remained
cartilaginous, and accordingly less specialized, and thereby
less prone to extinction.
It should also be mentioned that when a structure is lost during
evolution it is rarely restored. Returning to the previous example,
the darters, tiny members of the perch family of fishes, have lost
the swim bladder, a loss which allowed them to invade swiftly flowing
freshwater streams. This example also can serve to offer an
alternative view to what the Darwinians would regard as an adaptation
to the swift stream environment. Isn’t it possible that the darters,
having lost the swim bladder, stumbled into the stream environment or
perhaps even sought it out? Admittedly this loss can be regarded as
adaptive but only with respect to that rather specialized environment.
Also, are we to believe that the loss of the swim bladder was a
gradual process as the Darwinian view would suggest? It would seem
that a great many evolutionary changes have involved instantaneous
specializations of one sort or another. This general tendency may
be yet another reason for extinction.
Leo Berg’s early insight into these matters was truly awesome.
He clearly recognized the role of preformation and epigenesis in
both phylogeny (evolution) and ontogeny (development) and supported
his convictions with a multitude of examples (Berg 1969). He was,
in my estimation, a true evolutionary prophet.
VII-3. Ontogeny and phylogeny compared
The present contains nothing more than the past, and what is
found in the effect was already in the cause.
— Henri Bergson
According to Darwinian doctrine and Crick’s central dogma, DNA is
not only the depository and the distributor of the information but
its sole creator. I do not believe this to be true.
— Pierre Grassé
There is no question that all of the information necessary to produce
a unique human being is contained in a single cell, the fertilized
egg, a mere tenth of a millimeter in diameter. While the information is
preformed, the development of the individual is largely epigenetic.
I now suggest that precisely the same relationship may exist with
respect to phylogeny (evolution). Viewed in this manner, both
development and evolution result from the organized and progressive
activation (derepression) of an incredibly enormous storehouse of
potentialities. I realize that this suggestion seems ludicrous at
first sight when applied to the evolutionary process, yet I feel it
is necessary as it can offer an explanation for a number of otherwise
baffling realities. Of cardinal importance is the question — Where
did all the information come from? If, as is so obvious at the onset
of ontogeny, the information were also present from the start of the
evolutionary process, someone or something had to put it there. That
same someone or something apparently produced the inanimate world with
all its rules, laws and precise mathematical relationships. It is
my understanding that information does not arise de novo, but must
have a source. In that sense I agree with Grassé as quoted above.
It should also be noted that Schindewolf, Goldschmidt, Berg and Grassé
all subscribed to preadaptation during evolution, a consideration that
demands the presence of meaningful information prepared in advance,
i.e. preformed. These conclusions are nothing more than the
extrapolation to the living world of Albert Einstein’s conviction
– “I shall never believe that God plays dice with the world.”
Once again, I insist that the only alternative to chance is design,
which in turn implies purpose. Let me also add that I fail to see how
this perspective can in any way interfere with the search for ultimate
truth. On the contrary, I have come to regard it as a liberating
asset in that endeavor!
There is an entirely different reason to take this suggestion
seriously. It can offer insights into a number of otherwise enigmatic
observations from comparative biology. Two of these have already been
mentioned: the presence of a placenta in certain sharks and the
remarkable ciliate protozoan Diplodinium ecaudatum (Figure 8 ).
The Onycophoran worm Peripatus, with its strange combination of
arthropod and annelid characters, can seem perfectly reasonable
from this perspective. Incidentally, Peripatus also nourishes
its developing embryos with a kind of placenta as was noted by
Berg (1969). Thus, Peripatus combines features of three different
taxa: Annelida, Arthropoda and the placental Mammalia. The primitive
chordate Amphioxus (Branchiostoma lanceolatus), while it has all three
chordate structures (gill slits, a dorsal hollow nervous system
and a notochord), possesses a kidney consisting of solenocytes
of the protonephridial (flame cell) type characteristic of the
Platyhelminthes (flatworms), the Aschelminthes (roundworms) and
the polychaete Annelida, none of which could possibly be regarded
as its close relative. On the other hand, certain oligochaete
annelids (earthworms) have a tubular kidney system more like that of
vertebrates. The Apoda (limbless amphibians) have large yolk-laden
eggs suspended by albuminous chalazae closely resembling the situation
in the cleidoic (shelled) eggs of reptiles and birds. They lack only
the calcareous shell. Other strange evolutionary puzzles such as
the egg-laying monotreme mammals (the Platypus and the Echidna) are
commonplace in comparative zoology, yet can suddenly become reasonable
within the preformation context. When it comes to the possible
combinations of characteristics one can almost say — Anything goes!
The plant kingdom abounds with similar examples such as the
occurrence of distantly related plant species producing similar,
if not chemically identical, flavors of lemon, orange, anise, apple,
pineapple, cinnamon and a host of other pleasant aromas so valuable
to our cuisine. They may simply have drawn from the same common
storehouse of available information.
The morphological similarities which exist between the Orthopteran
leaf and stick insects (Phasmodea) and the plants which they inhabit
acquire simple explanations in this light. Berg (1969) noted that
the eggs of one of these insects (Phyllium crurifolium) closely
resemble, both internally and externally, the seeds of the plants
(Umbelliferae) with which it is commonly associated and, like the
seeds, are scattered on the ground where they may remain for up to
two years. These symbioses need no longer seem baffling if one simply
assumes that the informational potential was available to both the
plant and animal kingdoms when those evolutionary events occurred.
A similar argument would apply to the origins of the structural and
behavioral reciprocities that often exist between flowers and their
insect pollinators. As another example, the tunic of the sea squirts
(Urochordata) is composed of cellulose, otherwise a plant product.
The list could go on and on.
Of course how all this was effected remains a total mystery, but
this perspective at least avoids assuming a Lamarckian mechanism
for which no evidence has been forthcoming. Similarly, the whole
phenomenon which has been described as convergent evolution can
now take on an entirely new significance as the selection of very
similar morphologies drawn from a universal stockpile of preformed
potentialities which were available when those evolutionary events
took place. In other words, what has been described as convergent
evolution is not really that at all, but rather an identity already
established (preformed). Unfortunately, since evolution seems no
longer to be in progress, we may never be able to directly observe
such transformations.
Now! Now! cried the Queen. Faster! Faster!
— Lewis Carroll
It is of interest to compare the predictive value of the Darwinian and
semi-meiotic models with respect to evolutionary rates. The Darwinian
view predicts long periods of gradual change with many intermediate
forms. The semi-meiotic concept is the very antithesis, with new life
forms being produced instantly as a result of the cytological events
which occur during the first meiotic division in oocytes bearing one
or more chromosome rearrangements in heterozygous form. As I
indicated earlier, one half of the products of oocytes bearing a
single heterozygous rearrangement will be like the original type and
one half will be a new chromosome structural homozygote and, possibly,
a new and discrete species. As improbable as this may seem at first
glance, it is nevertheless precisely what the semi-meiotic hypothesis
predicts — namely, instant speciation. The time constants for
this process would then be on the order of minutes, or even seconds,
rather than the extensive periods of time required by the Darwinian
model. This suggestion remains in complete agreement with
Schindewolf’s recommendation that we might as well stop looking for
the missing links as they never existed. I wholeheartedly agree!
The semi-meiotic hypothesis also puts the origin of Homo sapiens
in a whole new perspective. Since we coexisted with and were preceded
by Neanderthal man, isn’t it possible that he (or rather she to be
precise) was our instantaneous predecessor with no intermediates
involved in the process?
It would be fascinating to be able to reproduce the Neanderthal
karyotype, as it could be an acid test of the semi-meiotic hypothesis.
I suggest that the two karyotypes might differ only by one or a few
structural rearrangements, perhaps only by a single homozygous
inversion. I would also anticipate, for reasons already discussed,
that the Y (male determining) chromosomes might prove to be quite
dissimilar.
VII-5. Has evolution been guided?
I want to know God’s thoughts … the rest are details.
— Albert Einstein
The most beautiful thing we can experience is the mysterious.
It is the source of all true Art and Science.
— Albert Einstein
Men despise religion. They hate it and are afraid it may be true.
— Blaise Pascal
The cure for this is first to show that religion is not contrary
to reason, but worthy of reverence and respect.
I am aware of the negative effect this query may have on certain
members of the intellectual community. Nevertheless I feel it is a
perfectly valid, and thereby a scientific, question since the role
of chance is, to say the very least, questionable. This question
is intimately related to the question — Are there laws governing
evolution? I realize that some distinguish between those laws that
they regard as natural and those that they reject as being unnatural,
mystical or otherwise unacceptable. I see no reason to make those
distinctions. Laws are laws whether or not we like them or understand them. For example, everyone accepts the reality of gravitation and Galileo’s equation relating the distance of falling objects to time. However, no one as yet understands the cause of gravity. Thus, neither in religion nor in science does acceptance demand
understanding.
If not chance, it seems to me that the only rational alternative is that both evolution and development have indeed proceeded according to law just as Leo Berg has insisted. The only real unknown is the nature and purposes of the law maker or makers. Don’t our representatives in congress usually have some purpose in mind when they enact legislation? Also, seriously considering the possibility of guidance may serve to ameliorate the unfortunate situation which continues to separate the religious and scientific communities. Is it not possible that both perspectives might be correct? I have come to believe that it is and, in so doing, join with Albert Einstein: “Science without religion is lame, religion without science is blind.”
I will address this issue first with the views of others and finally with a single apparent fact from the fossil record. Some of our greatest intellects have been physicists. In addition to Pascal, Galileo, Newton, Faraday and of course Einstein, among many others, all acknowledged God one way or another. More recently, Richard P. Feynman (1998) compared scientific discovery to a religious experience. L.C. Dunn (1965) pointed out that Mendel’s data are so nearly ideal that his paper might be considered a demonstration, rather than a test, of the laws that now bear his name. It is fair to say that we still have not identified the source of bright ideas, insights and creative acts of genius. Mendel, as the abbot of his Augustinian monastery, at least serves as an example that one need not be an atheist to conduct first class research!
In contrast with the great physicists I have mentioned, why so many biologists remain professed atheists or agnostics is a complete mystery to me. Every aspect of both the living and nonliving world is totally at odds with those positions. Nevertheless, the Darwinians continue to insist that all of evolution is the result of mere chance events. Stephen J. Gould has recently compared the evolutionary process to a drunk reeling back and forth between the bar room wall and the gutter (1996, page 149). He has also described intelligence as an “evolutionary accident”. I will only say that it was some accident! Richard Dawkins’ Selfish Gene, Blind Watchmaker, and Climbing Mount Improbable require no further comment from me.
When Alfred Russel Wallace first expressed his views they were essentially identical with those of Charles Darwin. The question arises whether Darwin would ever have published the Origin had it not been for Wallace. We do know that Darwin had entertained the mechanism of natural selection for several years and that he was
urged by his friends to publish in order to establish priority. The important point here is the way in which these two naturalists subsequently came to differ in their interpretation of the evolutionary process. While Darwin remained steadfast, Wallace underwent at first a partial and then a complete intellectual metamorphosis which is obvious from the complete title of his last book — The World of Life: A Manifestation of Creative Power, Directive Mind and Ultimate Purpose (1911).
I quote from the penultimate paragraph of his Preface because it reflects precisely my own feelings with respect to the semi-meiotic hypothesis.
I also wish to point out that, however strange and heretical some of my beliefs and suggestions seem to be, I claim that they have only been arrived at by a careful study of the facts and conditions of the problem.
I now offer but a single observation that bears on the question of whether or not evolution has been guided. It relates to Robert Broom’s opinion that not a single new genus has appeared in the last two million years. It would seem that the last genus was Homo and the last species Homo sapiens.
I rest my case.
VIII. Conclusion
Facts which at first seem improbable will, even on scant explanation, drop the cloak which has hidden them and stand forth in naked and simple beauty.
— Galileo
No biologist worthy of his reputation can limit himself to criticism of accepted doctrine, however necessary and valuable it may be; he has to construct, and is able to do so if he can discard accepted ideas and view evolutionary phenomena from new angles in the light of recent advances in paleontology and molecular biology.
— Pierre Grassé
It is in the spirit of the above quotation from Grassé’s book
(1977) that I have presented this material.
The most convincing thing in favor of the semi-meiotic hypothesis is the independence with which so many virtually identical conclusions have been reached by so many of my distinguished predecessors.
For example, Grassé (1977) made no mention of Broom, Huxley and Petrunkevitch but reached the same conclusion that evolution is largely finished and has been for millions of years. Similarly, Broom and Schindewolf independently reached the conclusion that the individual is the unit of evolutionary change. Berg reached the same conclusion as Punnett, Osborn and Bateson that the role of selection is to prevent change rather than to produce it, a conclusion also reached by Grassé (1977, page 119). Goldschmidt, Schindewolf and Berg all concluded that saltation is the mechanism for all significant (trans-specific) evolutionary change. Both
Grassé and Berg emphasized internal (endogenous) factors as of great evolutionary significance yet neither mentioned the other. Grassé and Schindewolf both maintained that evolution is irreversible. Luther Burbank and William Bateson each independently questioned the capacity of sexual reproduction to support evolutionary change. These were not mere coincidences but reasoned conclusions reached after
a careful consideration of all the facts which were then available. None of this can be accommodated within the Darwinian model. We owe these men a great debt. Referring back to Robert Burton whom I quoted
in the dedication, let me say that I am the dwarf standing on the shoulders of these great investigators. It will be with a sense of great personal satisfaction if I am able to help place these scholars in their rightful and long overdue positions as enlightened pioneers in the exploration and clarification of the great mystery of evolution.
Every shred of tangible evidence points to sexual reproduction as a highly conservative device, serving only to bring evolution to a virtual standstill. Just as William Bateson indicated even before 1900, I too find it amazing how long the Darwinian view has prevailed in the face of an enormous and continually growing body of information with which it cannot possibly be reconciled.
In short, Darwinism must be abandoned as a meaningful instrument of organic change.
I realize that paradigms are expected to be replaced before they are discarded. It is with that end in mind that I have continued to pursue the semi-meiotic hypothesis. I have time and again tried to discredit it and have failed. I invite others to attempt the same. Let me also add that I cannot conceive of any other device that could have operated to produce the sort of evolutionary changes that we know have taken place. Furthermore, the semi-meiotic hypothesis remains in complete accord with all that I have been able to glean from the experimental and descriptive literature in embryology, cytology, paleontology, taxonomy, comparative and general anatomy, comparative and general physiology, biochemistry and genetics.
A second consideration has to do with the nature of the scientific method. Scientists have traditionally relied on experiment to discover the truth. Embryology, Biochemistry, Physiology and Genetics all have progressed through experiment. Where is Experimental
Evolution? I submit that in the past there was great interest in
Experimental Evolution, but since the findings were largely negative
they were not published. In all fairness, I must acknowledge that
Schindewolf was steadfastly opposed to the idea of Experimental
Evolution and maintained that it cannot be investigated in that
way (1993, page 311). I remain unconvinced that he was correct
on this most critical point. The semi-meiotic hypothesis is
eminently testable in suitable material. I am optimistic that this
hypothesis may offer an experimental opportunity to provide insight
simultaneously into the two greatest unsolved problems in all of
biological science, the other being the mystery of embryonic
development. The two are unquestionably intimately related
just as Leo Berg so clearly recognized long ago.
Thus, while evolution may or may not be finished, I remain hopeful
that we have the capacity to produce new and hitherto unknown higher
life forms (true species or perhaps even higher taxonomic categories)
in the laboratory. I predict that this goal may be realized through
the experimental inhibition of the second meiotic division in female
animals that either are heterozygous for chromosome structural
rearrangements or that bear oogonia that are. Experiments to
realize that end are in progress.
To slightly modify an old adage: “God works in mysterious
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(c) Copyright 2000 by John A. Davison.
Latest modification July 15, 2000.
This document and others by the same author may be found on-line at:
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