Too many sisters affect male sexuality

October 21, 2010

Growing up with lots of sisters makes a man less sexy. For rats, anyway. A new study published in Psychological Science, a journal of the Association for Psychological Science, finds that the sex ratio of a male rat's family when he's growing up influences both his own sexual behavior and how female rats respond to him.

David Crews, a psychobiologist at the University of Texas at Austin, is interested in how early life affects behavior later. This is an area that has received a lot of attention recently, such as research showing that the position of a fetus in the matters. For example, a female fetus that spends the sandwiched between two brothers grows up to be more masculinized, because she's been exposed to their hormones. Other researchers have found that sex ratio of the litter itself affects adult behavior. But Crews wanted to separate the effects of life before and after birth. "Life is a continuous process: you're a fetus, then you're born into a family. Each one of these periods can be important," he says—and they don't necessarily have the same effects.

When rat pups were born, the researchers counted the number of males and females in each litter to determine the sex ratio in the womb. Then they reassembled litters in three ways: so the litters were balanced between males and females, strongly male-biased, or strongly female-biased. Then they observed the mother's behaviors toward their pups and, once the males grew up, tested them to see how they behaved with sexy female rats.

The researchers found no effects of the sex ratio in the uterus. But they did find differences in behavior based on the kind of litter in which the males grew up. When males who were raised with a lot of sisters were presented with receptive female rats, they spent less time mounting them than did male rats that were raised in male-biased litters or in balanced families. But they penetrated the female rats and ejaculated just as much as did the other males. This means "the males are more efficient at mating," Crews says.

The males may be compensating for the fact that they're less attractive to females. You can tell this by watching the females—if they want to mate with a male, they'll do a move called a dart-hop, says Crews, and "they wiggle their ears. It drives males nuts." The females did this less when they were with a male rat that had grown up in a female-biased litter. Crews carried out the study with Cynthia B. de Medeiros, Stephanie L. Rees, Maheleth Llinas, and Alison S. Fleming of the University of Toronto at Mississauga.

These were rats, but the results have implications for humans, too, Crews says. "It tells you that families are important—how many brothers and sisters you have, and the interaction among those individuals." Families are particularly important in shaping personalities, he says. The environment where you were raised "doesn't determine personality, but it helps to shape it."

Related Stories

Recommended for you

Study links cannabis use in adolescence to schizophrenia

April 26, 2017

Scientists believe that schizophrenia, a disorder caused by an imbalance in the brain's chemical reactions, is triggered by a genetic interaction with environmental factors. A new Tel Aviv University study published in Human ...

Cognitive skills differ across cultures and generations

April 25, 2017

An innovative study of children and parents in both Hong Kong and the United Kingdom, led by University of Cambridge researchers Michelle R. Ellefson and Claire Hughes, reveals cultural differences in important cognitive ...

8 comments

Adjust slider to filter visible comments by rank

Display comments: newest first

Milou
5 / 5 (3) Oct 21, 2010
Rats! I have four sisters and no brother. I am doomed.
eauzones
5 / 5 (2) Oct 21, 2010
Your username wouldn't help either
Skultch
not rated yet Oct 21, 2010
You're not doomed. Just don't look to women for how to act. You need as many male role models as possible. You can fight your biology, it's just harder.
Taps
not rated yet Oct 21, 2010
"When males who were raised with a lot of sisters were presented with receptive female rats, they spent less time mounting them than did male rats that were raised in male-biased litters or in balanced families. But they penetrated the female rats and ejaculated just as much as did the other males. This means "the males are more efficient at mating," Crews says"

This explains everything. I was a single child and have been a loner and monk for most of my life, LOL. I could mate, but most females have so much baggage that comes with them, I lose interest soon after. I just don't feel like supporting 2.5 kids, 3 cars, a house mortgage, 2-3 pets, weekly $300 grocery bill, etc. God forbid there is a divorce!
Husky
5 / 5 (1) Oct 21, 2010
hence the term sissy boy
thales
3 / 5 (2) Oct 21, 2010
My dad has 5 sisters and no brothers. I wish I hadn't read this article.
Quantum_Conundrum
not rated yet Oct 23, 2010
I could mate, but most females have so much baggage that comes with them, I lose interest soon after. I just don't feel like supporting 2.5 kids, 3 cars, a house mortgage, 2-3 pets, weekly $300 grocery bill, etc. God forbid there is a divorce!


That's why you gotta find a woman who makes the money, $100k+. Pharmacist, Nurse Educator, etc. They're out there. I've done a few couple's tax returns where the woman made 2 or 3 times as much as the man. Smartest guys in the world, lol.
freethinking
5 / 5 (1) Oct 24, 2010
Ha... you all are rats every last one of you!!! :)

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.