The Science of Sex: Lesbian Lizards

On a parched, wind-swept lakebed in southeastern Arizona, within earshot of the trucks hurtling by on Interstate 10, a strange experiment of nature is playing itself out — an experiment that might shock moral conservatives but should delight lesbian separatists everywhere. Two species of whiptail lizards have interbred, producing a new, all-female species. These animals have sex with each other and produce baby lizards without any help from males. And the babies grow up to be lesbian too.

Zoologist David Crews of the University of Texas at Austin discovered the unusual sexual behavior of Cnemidophorus uniparens, as the all-female species is called, in the late 1970s, and has been working on them ever since. Crews doesn’t use the word “lesbian” — he prefers the neutrality of scientific jargon like “parthenogenetic unisexual pseudocopulators” — but it’s hard to ignore the parallels.

A sexual encounter between two of these female animals is very similar to that between a male and female lizard of the species that gave rise to C. uniparens. One animal takes the “male” role, courting the “female” with rapid tongue-flicks around her head. If “she” is receptive, “he” grasps the nape of her neck in his mouth, climbs onto her back and swings his tail under hers so that their genital regions are in contact. Then he switches his jaw-grip to her pelvic region, so that his body loops around hers like a doughnut. The two animals remain in this posture for a few minutes before they disentangle themselves and go their separate ways.

Any particular lizard will show either “male” or “female” behavior, depending on where she is in her ovarian cycle. If she is in the pre-ovulatory phase (when eggs are maturing in her ovaries), she will show “female” behavior; if she is in the post-ovulatory phase (when the eggs move down her oviduct and acquire their shells), she will show “male” behavior. So there are no “butches” or “femmes” among the lesbian lizards: they are more like switches who can go either way.

Being female, the C. uniparens lizard lacks a penis; in fact, she lacks two penises, the proper number for male lizards. She also lacks testes. So there is no actual sexual penetration or transfer of sperm — hence the term “pseudocopulation.” Genetically speaking, the offspring are parented only by the female who lays the eggs, so it’s a case of parthenogenesis (virgin birth, in other words). What, then, is the point of the sexual encounter? Is it just an instinctual or atavistic response — an ancestral behavior that the new, all-female species hasn’t got around to eliminating?

According to Crews, it does have a function. Early in his study of the all-female lizard, he and his students found that lesbian sex increases the animals’ fertility. Lizards that were prevented from engaging in female-female sex laid eggs less often and laid fewer eggs on each occasion. In a wide variety of species, including lizards, copulation is known to trigger reflexes that promote egg development or ovulation, and this function is preserved in C. uniparens.

Crews’ more recent work has involved studying the molecular and genetic mechanisms that regulate sexual behavior in the lesbian lizards. For example, he has shown that “male” behavior, which in humans is largely dependent on testosterone, is triggered by progesterone in the lizards. The drop in estrogen and rise in progesterone at ovulation causes the switch in sexual behavior.

Lesbian humans shouldn’t read too much into this research. It will be a long time from now, if ever, that male-free parenting becomes a reality in our own species. No mammal has ever learned the trick of reproducing parthenogenetically. That’s probably because of a process called imprinting, which makes it necessary for a mammalian embryo to receive its genes from both a male and a female parent.

What’s more, the lesbian lizards may be doomed to eventual extinction: without the mixing of genes that male-female sex confers, each generation is a clone of the previous one, and that makes it difficult to get rid of harmful mutations. Only a few odd invertebrates have managed to do without sexual reproduction for long periods of time.

Still, if nothing else, C. uniparens offer a little lesson in diversity: a challenge to our concept of what is “natural” and what is not. So, if you’re heading east from Tucson, why not turn south on Highway 666 to Cochise, hike out onto the lakebed and look for a slim, long-tailed lizard with five light stripes down its back? She’ll be the one with the self-reliant swagger.