In a recent post in which I questioned the claim that over 100 mutations get fixed in the human population in every generation, I remarked, “I’m happy to be proved wrong.” Guess what? I meant it. After weighing the evidence presented on both sides, I’ve decided that there are no good mathematical arguments showing that 130 mutations couldn’t have been fixed in each generation of the human lineage, over the past five million years. Although the equations of population genetics are based on assumptions, these assumptions have been tested – and validated – for bacteria. And while the mutation rate per individual per generation is five orders of magnitude greater for human beings than for bacteria, the fact that the human genome is about 1,000 times larger than that of a bacterium, coupled with the fact that there are multiple cell divisions per generation in animals, explains why humans would have a much higher mutation rate. Of course, arguments from extrapolation aren’t always valid, and for all I know, there might be any number of reasons why fixation rates of 100 per generation for human beings (as predicted by the equations of population genetics) are biologically implausible. But the onus is clearly on the skeptic to explain why we shouldn’t believe the claim that 100 mutations are fixed in the human population in every generation. Dr. Kozulic (who is a well-published biochemist) is a prominent skeptic; and in my last post, Branko Kozulic responds to Professor Moran, I gave him the opportunity to state his case. Since Dr. Kozulic is from Croatia, I also assisted him in presenting his argument as clearly as possible, in English. After sifting through the replies by wd400 and Nick Matzke, I have come to the conclusion that the arguments that Dr. Kozulic and I presented in our post failed to establish that a fixation rate of 100 per generation for human beings, even during the Paleolithic era, would be infeasible. To uninitiated laypeople like myself, such a high rate of fixation for a very thinly scattered Stone Age population sounds highly counter-intuitive at first sight, but that does not make it untrue. After weighing the arguments, I now think that the neutral theory of evolution can account for the number of mutations fixed in the human population over the last five million years (roughly 22.4 million).
My concession on this point does not mean that I think the neutral theory of evolution can account for the pattern of fixation events observed in the human lineage, let alone the existence of orphan genes. Those are separate issues, and should be addressed as such.
After reading Professor Moran’s recent post, On being “outed” as a closet Darwinist, I would like to make it clear that I am fully aware that Moran publicly disagrees with many of Darwin’s ideas. In our previous post, Dr. Kozulic and I characterized Professor Moran as a “Darwinist” in one important respect only, as we expressly stated. To illustrate what I mean, I’d like to quote from his 2006 essay, Macroevolution:
The Creationists would have us believe there is some magical barrier separating selection and drift within a species from the evolution of new species and new characteristics. Not only is this imagined barrier invisible to most scientists but, in addition, there is abundant evidence that no such barrier exists. We have numerous examples that show how diverse species are connected by a long series of genetic changes.
If Professor Moran can think of a handy label to describe someone who holds such a view, then I shall gladly use it in future, when referring to him. “Gradualist” is a term that comes to mind, but I don’t think Professor Moran would appreciate that label, either. Moran also rejects the view that microevolution is sufficient to account for macroevolution, as his essay makes clear.
Professor Moran and I disagree on many things, and I’m sure we’ll have many lively exchanges in the future, but it would be downright churlish of me not to acknowledge that my attempts to show that the neutral theory could not account for 22.4 million mutations arising in the human lineage over the last five million years have failed. I also wish to state that I had no intention of giving any offense to Professor Moran in our exchange of views, and that I have always striven to remain as polite as possible, while publicly disagreeing with him. The next time I’m dining out, I shall order a glass of red wine and silently toast him.
Before I finish this post, I’d like to quote a passage from Dr. Kozulic’s 2011 paper, Proteins and Genes, Singletons and Species – a paper which I have cited on numerous occasions, on Uncommon Descent:
If just 200 unique proteins are present in each species, the probability of their simultaneous appearance is one against at least 104,000. [The] Probabilistic resources of our universe are much, much smaller; they allow for a maximum of 10149 events [158] and thus could account for a one-time simultaneous appearance of at most 7 unique proteins. The alternative, a sequential appearance of singletons, would require that the descendants of one family live through hundreds of “macromolecular miracles” to become a new species – again a scenario of exceedingly low probability. Therefore, now one can say that each species is a result of a Biological Big Bang; to reserve that term just for the first living organism [21] is not justified anymore.
The fallacy in the logic here should now be apparent. There is no reason to suppose that one singleton has to be fixed in the population before another one can be. The paper has therefore failed to demonstrate that speciation is an event that lies beyond the reach of chance.
An excellent case can be made that not only the emergence of life, but also key events in the history of life such as the Cambrian explosion, in which 30 novel body types emerged over a relatively short span of 20 million years, were events whose occurrence lies far beyond the reach of chance. Intelligent Design is on very strong ground here. However, I now believe that the argument that speciation itself is equivalent to a Biological Big Bang is a much weaker one. The origin of orphan genes remains an ongoing scientific mystery, but we should be wary of making a mountain out of a molehill. The imputation of design in this case would require much stronger supporting calculations than we have seen to date, and the mathematics contained in these calculations also needs to be very carefully scrutinized. During this time of scrutiny, we must be our own harshest critics. In a 2013 post on Uncommon Descent, I suggested that the “edge of evolution” may lie at the species level, using the definition of “species” employed in Dr. Kozulic’s paper. It appears that I spoke too soon. I think it is fair to say that the question of where the edge of evolution lies has now been thrown open again.