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.


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  • Pitou

    Not for nothing..

    I have 2 brothers (one absent a lot, the other is 16 yrs younger then me), 8 sisters. I’m 3rd from the top, and wicked close with most of the girls.

    I’ve never had an interest in “mounting” females.

    As much as I believe you are born gay, I also believe your surroundings in childhood play an important role in you developing the way you are supposed to develope. I don’t necessarily think that your surroundings in childhood play such a major role in “making” you Gay.. though I do think it helps you with a better understanding and greater acceptance of who you really are.

    It’s usually not your Mom’s and Sister’s that you’re typically afraid of coming out to… and to me that speaks volumes.

  • Kirsten

    Have there been any studies about lesbians having brothers? just curious because i’m a lesbian that was raised with 4 older brothers. I think nature is a bigger factor than nurture but both have an influence

  • Fitz

    Or maybe it means that parenting couples that create females are more likely to create a gay male than a straight one. So— maybe our folks had a different hormone combination than our straight gym-friend’s parents? Too many variables for this to be meaningful.

  • Jeffree

    Studies on humans have shown that there’s a positive correlation between the number of elder brothers a male has & the likelihood he will be/is gay. That doesn’t necessarilly mean it CAUSES him to be gay, just that the two go, um, hand in hand.

    I think there was a thread here at some point & we also studied that hypothesis in a stats class.

    The possible “expression” of male homosexuality in rats versus human may be different because of different development patterns in-utero & after birth—I’m just guessing because biology isnt my forte at all !

  • B210

    LOL almost all gays I know have one or more older sisters. I don’t have time to research it but IIRC most gay celebs/actors are the same way.

  • FYI

    Maybe nothing to do with “gay” rats (like in the HRC), but an interesting article at the link below about brain difference between Gay men, Lesbians, and heterosexuals.


    “Activity within the brain’s amygdala—an almond-shaped structure inside each brain hemisphere that is associated with processing and storing emotions—were compared between homosexuals and heterosexuals of both genders. The results showed that the brains of straight men and lesbians as well as and straight women and gay men share similar characteristics. Image courtesy of National Academy of Sciences, PNAS (copyright 2008)”

    For the full article, clink on the link below:


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