Sexual Promiscuity All Relative: Guys With Sisters Have Less Game

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Could the number of sisters a guy grows up with affect his sexual behavior later in life? Psychologists from the University of Toronto and the University of Texas suspect so after conducting a study on the sexual activity of rats. The study suggests that male rats from litters comprised mostly of girls are less promiscuous later in life, as well as considered less attractive by females.

At the start of this study, researchers wanted to learn whether the number of brothers and sisters a rat had influenced its sexuality. Specifically, they looked to see whether hormones in utero would alter a rat sexually.  Shortly after birth, litters were counted to determine whether rats were in the womb with mostly males, females or a fairly even gender distribution.  The researchers then reshuffled the babies among the mothers into new “family” groups to determine whether their upbringing would have more of an impact on sexual development as well.

Ultimately, the gender breakdown for rats in the uterus had no noticeable impact on their subsequent sexual behavior.  However, the males who were raised alongside plenty of sisters showed marked sexual differences than the males with ample brothers or an ratio of siblings.

Males raised with multiple sisters made fewer sexual advances on potential mates in their post-pubescent years.  This is not to say, however, that they had inactive sex lives; in fact, the male rats with many sisters had sex just as frequently as the other males.  In essence, the males who were raised alongside girls either were better at picking up on when a female was interested or had a better success rate in ultimately sealing the deal.  That, or perhaps they just weren’t as interested in foreplay.

One thought is that sexual attraction, in part, stems from a draw to the unknown.  Males who are less familiar with females are bound to be more curious about them, prompting them to make more sexual advances in adulthood, whereas the males with sisters wouldn’t need to be as inquisitive.

The research also discovered the female rats’ interest in the males. Unfortunately for the males with many sisters, potential female mates didn’t find them as attractive.  For whatever reason, females were more likely to flirt with, posture for and make sexual advances on males that had grown up with more brothers. Rats raised with other guys might have developed more masculine traits than those without brothers.

While the rat-focused study is interesting, it may be hard to make big leaps with associations to human sexuality. There are still plenty of variables that require further investigation to get a real handle on the sexual development of rats, let alone humans. Nonetheless, as one author of the study David Crews recently said, “It tells you that families are important–how many brothers and sisters you have, and the interaction among those individuals.” So if you’re a guy with a lot of sisters, take heart that while you may be less likely to be a ladies’ man, you’ll still lead a healthy sex life.

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