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Alligator sex determination: a real nightmare for evolutionists
E. Norbert Smith, Ph.D.

Female American Alligator, Alligator mississippiensis defending her nest at the Welder Wildlife Refuge in South Texas. Photo taken during the filming of the TV documentary, A smile for the Crocodile by the British Broadcasting Company. Photo by Dr. Smith.

Alligator reproduction: Alligators must be approximately six feet long (8-10 years old) to breed. Most females breed 3 out of every 4 years. They construct a large nest of available vegetation and deposit an average of 47 eggs near the top. They then cover eggs with more vegetation. Alligator eggs require 9-12 weeks to hatch and are incubated by the sun and heat 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. She remains nearby to defend the nest from predators and to assist the hatchlings from the nest. Even then in some areas raccoons destroy nearly half the nests and eat the eggs. A few days before hatching the baby alligator inside the egg shell start making a grunting sound. This keeps the mother nearby and synchronizes the hatching so all the baby alligators emerge from the eggs within a few hours. The mother alligator must carefully remove the nest material from the eggs to release the hatchlings. If the mother has been killed all the young will remain imprisoned inside the nest and die. Mother alligators have been seen gently breaking the egg shell with their teeth when a baby alligator has difficulty hatching. Mothers sometimes carefully load the baby alligators into her mouth and carry them to the water where she releases them and returns to the nest for another load. Such maternal care is uncommon among reptiles and was quite unexpected by evolutionists. They thought maternal instincts did not evolve until the appearance of birds. God made all living things optimally adapted for their environment.

Fertile alligator eggs inside the alligator nest. They are about the size and shape of chicken eggs, but the shell is leathery and flexible when first laid. Photo by Doc Smith at the Welder Wildlife Refuge.

Surprisingly it is incubation temperature and not chromosomes that determine the sex of the baby alligators. This presents some difficult problems for evolutionists. It's not easy remaining an evolutionist when confronted with the facts of science! Photo by Dr. Smith at the Welder Wildlife Refuge in South Texas.

Alligator sex determination: The basics of alligator reproduction are well known and are widely shown on TV nature programs. What is less widely known is the average incubation temperature of the eggs in the nest determines the sex of the baby alligators. They lack sex chromosomes! The early work was done at the Rockefeller Wildlife Refuge and was reported by Ferguson and Joanen in 1982. (see below) Dr. Ruth Elsie and others have continued the work at the refuge. The best information currently available is with an average egg incubation temperature of 85 degrees F all the hatchlings will all be female. At a temperature of 89 degrees equal numbers of healthy male and female hatchlings result. At 91 degrees only males are produced. The investigators actually admitted in the original paper that, "There has been no demonstration of a selective evolutionary advantage of the occurrence of TSD (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 more common method of having sex chromosomes. If there is some advantage of TSD why then do most animals still rely on sex chromosomes? These are difficult problems for evolutionists, but there is an even worse problem. Indeed even if one could conjure up an alleged selective advantage for such results in crocodilians the argument runs amuck with the consideration of turtles. In turtles higher temperatures produces females not males! The notable exception is Trionyx spiniferus the spiny soft-shelled turtle which have sex chromosomes and sex of the hatchlings is unaffected by egg incubation temperature (Bull and Vogt, 1979).

Hard pressed evolutionists: All this leaves the poor evolutionist in a difficult situation. Whatever arguments that could be fabricated to support one mode of sex determination disintegrates when one considers the other group. Could this whole sex-in-response-to-temperature thing have been designed by a Creator with a sense of humor? It seems to me this takes far less faith to accept than 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. It really is difficult remaining an evolutionist! I know, for I couldn't do so after looking objectively at the facts. Can you? Should you? Perhaps most surprising is you can actually have a personal relationship with the Creator of turtles, alligators and people.


M. W. J. Ferguson and T. Joanen. 1982. Temperature of egg incubation determines sex in Alligator mississippiensis. Nature 296:850-852.

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

Investigate evolution. Its unscientific.