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How alligators become he’s or she’s – by an expert

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According to Norbert “Doc Gator Smith”


The sex of most vertebrates is determined genetically by sex chromosomes. Crocodilians and some turtles do not have sex chromosomes and sex is determined instead by the incubation temperature of the eggs. For alligators, an average incubation temperature of 85 degrees Fahrenheit produces only female hatchlings. At a temperature of 89 degrees equal numbers of males and females result and at 91 degrees only males are produced.

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Such problems regarding evolution are not covered by the media nor are they mentioned in textbooks or discussed in biology classrooms. One of these persistent issues is related to the determination of sex in certain reptiles including alligators and turtles. I caught and studied hundreds of these fascinating creatures at the beautiful Welder Wildlife Refuge in south Texas.

Alligators must be eight to ten years old and approximately six feet long to breed. Most mature females breed three out of every four years. They construct a large nest near the water from nearby vegetation. When the nest is complete they deposit an average of forty-seven eggs in a depression near the top of the nest. After the eggs are laid, she covers them with more vegetation.

Alligator eggs require nine to twelve weeks to hatch and are incubated by the heat from the sun and heat produced by of the decaying vegetation. During the time the eggs are incubating, the female alligator has a restricted home range of less than a third of an acre and will actively defend the nest. Just her presence deters most natural enemies.

A day or two before hatching, the baby alligators inside the egg begin making a grunting sound which synchronizes hatching of the entire clutch.

Upon hearing the sound of her emerging young, the mother alligator carefully removes the nest material from the eggs and releases the hatchlings. If the female has been killed, the young alligators remain imprisoned inside the nest and die. Mother alligators have been seen gently breaking the egg shell with their teeth when a young alligator has difficulty hatching. The female will take each baby alligator into her mouth and carry them to the water where she releases them and returns to the nest for another one.

In areas where alligators winter in underground burrows the young stay with their mother the first two years. Such maternal care is uncommon among reptiles and is largely unreported by evolutionists.

It is also well established that pythons not only protect their eggs from predators, but encircle the eggs and produce heat to incubate them. Students are given missinformation and are told maternal instincts and caring for the eggs and young did not evolve until the appearance of birds. God is not restricted by evolution dogma and made all living things optimally adapted for their environment. God saw all that he had made, and it was very good (Gen 1:31a).

It is the incubation temperature and not chromosomes that determine the sex of baby alligators. This presents a difficult problem for evolutionists. Crocodilian reproduction is well known and often shown on television nature programs. Alligators and certain other reptiles lack sex chromosomes (Ferguson and Joanen, 1982). Ted Joanen and Larry McNease of the Rockefeller Wildlife Refuge in Grand Chenier, Louisiana taught me how to call, capture and safely handle alligators and I have returned to the refuge several times. Dr. Ruth Elsie and others continue the important alligator research at the refuge. The refuge has a higher concentration of alligators thanany other place in the world and is a beautiful place to visit, watch birds and observe alligators in their natural environment.

Research studies with alligator eggs have shown that an average incubation temperature of 85 degrees Fahrenheit yields only female hatchlings. At a temperature of 89 degrees, equal numbers of male and female hatchlings result. At 91 degrees, only males are produced. The investigators admitted in the original paper that, “There has been no demonstration of a selective evolutionary advantage of the occurrence of temperature sex determination in reptiles.” One is hard pressed to present an argument in favor of this sort of sex determination as opposed to the morecommon method of sex chromosomes. If there is a selective advantage, then why do most animals rely on sex chromosomes?

These are difficult for evolutionists to explain, but there is an even greater problem. If one could conjure up a selective advantage for such sex determination in with crocodilians, the argument runs amuck when turtles are considered. Most turtles also lack sex chromosomes and the sex of the offspring is determined by the average incubation temperature of the eggs, but there is a remarkable difference. In turtles eggs those incubated at higher temperatures produce females, not males! The notable exception is Trionyx spiniferus the beautiful spiny soft-shelled turtle which have sex chromosomes and the sex of the hatchlings is unaffected by the incubation temperature (Bull and Vogt, 1979).

This leaves the evolutionist with an unenviable situation. Whatever arguments are fabricated to support temperature induced sex determination in crocodilians disintegrate when one considers turtles. It is not surprising evolutionists are unwilling to address these important problems for they know they are standing on shifting sand. It is difficult to imagine some yet-to-be-conceived alleged advantage of allowing temperature to determine sex one way in crocodilians and the opposite way in most, but not all turtles. Once again it is not a good time to be an evolutionist. Those pesky facts continue unrelenting to give them nightmares which helps explain why tens of thousands of former evolutionists have abondoned evolution like rats leaving a sinking ship and are looking elsewhere for answers.

Perhaps there is another reason for this unusual mode of sex determination. Could this sex-in-response-to-temperature thing have been designed by a Creator who likes variety? Or perhaps He is simply showing a sense of humor. …


Bull, J. J. and R.C. Vogt. 1979. Temperature-Dependent Sex Determination in
Turtles. Science 206:1186-1188.

Davies, D., J. L. Thomas and E. N. Smith. 1982. Effect of body temperature
on ventilatory control in the alligator. J. Appl. Physiol. 52:114-118.

Ferguson, M. W. J. and T. Joanen. (1982). Temperature of egg incubation
determines sex in Alligator mississippiensis. Nature 296, 850-853.

Johnson, C. R., W. G. Voight and E. N. Smith. 1978. Thermoregulation in crocodilians—III, Thermal referenda, voluntary maxima and heating and
cooling rates in the American alligator. Alligator mississippiensis Zool. J.
Linn. Soc. 62:179-188.

Robertson, S. L. and E. N. Smith. 1979. Thermal indications of cutaneous
blood flow in the American alligator. Comp. Biochem. Physiol. 62A:569-572.

Robertson, S. L. and E. N. Smith. 1981. Thermal conductance and its relation
to thermal time constants. J. Thermal Biology 6:129-143.

Smith, E. N. 1974. Multichannel temperature and heart rate telemetry transmitter. J. Appl. Physiol. 36:252-255.

Smith, E. N. and W. E. Crowder. 1974. Implantable ECG transmitter employing a magnetic switch. J. Appl. Physiol. 36:634-635.

Well, wd400, if you have an answer, let's hear it. If it is not a just-so story, it may well be illuminating. It is better to say "we don't know yet" than to settle for a just-so story because the latter tends to be pleasant Darwinian noise rather than information. News
Sounds like more 'Darwin of the gaps' to me. humbled
wd400- the problem is your position "explains" everything, even if it can't support the explanation with actual science. Ya see to people like you and Nick Matzke, "a plausible evolutionary pathway" just means someone imagined it and told someone else about it. Joe
News, We don’t know, and no one else does either, why some reptiles have weird ways of assigning sex. This is why biologists don't take you guys seriously. Given an interesting pattern biologists will try an work out an explanation for it (what was the ancestral state for amniotes? Why would it be maintained in some lineages and changed in others? If their is an adaptive basis for this trait what are the fitness consequences likely to be...) You seem to want to stop at the "that’s actually a problem for your theory" rather than try to find out something about the world. wd400
NickMatzke_UD, do we really HAFTA put the coffee cup graphic in for you, every time someone cracks a joke? We thought the gator pix/footage would be more fun. For most readers, they probably were. We don't know, and no one else does either, why some reptiles have weird ways of assigning sex. They and we are all vertebrates, so you would think ... that's actually a problem for your theory whether you own it or not. Parental warning: Reptile sex is NOT DISCUSSED IN DETAIL HERE!!!. We can't afford to lose our family friendly rating. News
Perhaps there is another reason for this unusual mode of sex determination. Could this sex-in-response-to-temperature thing have been designed by a Creator who likes variety? Or perhaps He is simply showing a sense of humor.
Really? That's your preferred "scientific" explanation? God's sense of humor? Thanks for another good example of "God of the gaps" thinking -- specifically, the gaps in the knowledge of creationists/IDists who refuse to do the slightest background research before expounding on scientific topics. Here, let me google that for you: http://lmgtfy.com/?q=evolution+of+sex+determination NickMatzke_UD
A Gene, News put up Doc Gator's paper at his request. News
Even a pan-adaptationist wouldn't need to think there was some globally "best" way to determine sex. There a models that predict Temperature-dependent sex determination will be advantageous when males and females have better relative fitness in different environments - notably seasons. They certainly seem to explain a few real-world situations. wd400
Either News is beign naughty and quoting someone else without attribution, or Ms. O'leary has a little-known career as an alligator wrangler. Anyway, the variety of sex determination systems being a problem is only a worry for a pan-adaptionist. For the rest of us, there is no problem with the explanation that sex determination has evolved in different ways for different groups of organisms. A Gene

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