Having Lots Of Sisters Makes You Gay (If You’re A Rat)

And of course by “makes you” we mean “you’re statistically more inclined to be.” And by “gay” we mean “less straight.”

Following some 88 rats from birth through death, researchers at the University of Toronto researchers found that rats raised with more sisters were less likely to be interested in humping some lady rat rail. The fewer gals you grow up with, the more you want to do bad things to these gals.

Previous rat studies have shown that how mothers treat their newborns can influence whether genes in those newborns become activated or stay muted. Rat pups that are neglected can literally end up with worse brain chemistry — less serotonin, fewer glucocortinoid receptors — than identical twin siblings that were nurtured (usually by licking, which is sort of gross, but again: they are rats). […] In the new study, the 88 rats were kept in Plexiglas cages and subjected to a life of extreme leisure: they were fed ad libitum and kept at a constant 75 degrees F (24 degrees C). Rats hit puberty when they are about 60 days old, so the researchers started watching them especially closely around that age. I’m sure it was embarrassing for the rats, but the researchers watched as the males walked up a ramp and then mounted (or didn’t) some lovely classmates. The researchers even kept track of whether the males ejaculated.

The results showed that rats who grew up for those first 60 days with sisters were less likely to mount than the ones who grew up with brothers. It didn’t matter whether the rats had been in the womb with their sisters — only that they grew up in early life with sisters. The study suggests that psychology, not hormones or chemicals, is at work.

In those earlier studies, Dr. Marc Breedlove at Michigan State University played with hormonal changes, which also revealed less about gay rats than not entirely heterosexual rats.

Dr. Breedlove says he can take a male rat and make it behave like a female for the rest of its life, and vice versa for a female, just by altering the hormones it’s exposed to at birth. Because rats are born underdeveloped, that’s roughly the same as altering a third-trimester human fetus in the womb. But first, he said, Stahl would need a crash course in rat sex. Dr. Breedlove explained that male rats, including one he showed Stahl called “Romeo,” will mount any rat that comes their way. In the mating process, the female performs something called lordosis, where she lifts her head and rump. If Romeo goes after a male, Dr. Breedlove says the male will seem profoundly indifferent.

But Breedlove says he can change all that. He gave a female rat a single shot of the male sex hormone testosterone at birth. Now grown up, she will never perform lordosis. But a male rat did. He was castrated at birth, depriving him of testosterone. “So you created a gay rat?” [CBS’ Leslie] Stahl asked. “I wouldn’t say that these are gay rats. But I will say that these are genetic male rats who are showing much more feminine behavior,” he explained. So the answer may be that it’s not genes but hormones. “That’s exactly the question that we’re all wondering. This business of testosterone having such a profound influence. Does that have some relevance to humans?” Breedlove said.

Of course the question begs: Are gay rats more likely to give birth to a higher preponderance of gay rats? Let’s ask Ratatouille.

[Time]