What Makes Women Hot? Men Without Sisters (at Least for Rats)

(CBS) What makes a lady rat hot?

Apparently, men who don't grow up around too many women.

In a recent study of 88 rats, scientists found that the male rats that grew up around lots of sisters weren't getting as much action as their counterparts.

The reason? Females weren't giving the boys the special sex sign.

"They wiggle their ears. It drives males nuts," says David Crews, the University of Texas at Austin psychobiologist who ran the study.

That meant the male rats had fewer mounting opportunities, but apparently used them wisely. Researchers found they penetrated and ejaculated the female rats as often as male rats that didn't grow up with sisters.

In essence, when they got their chances, they took advantage. What does all of this mean for human Casanovas?

"It tells you that families are important," said Crews in a statement. "How many brothers and sisters you have, and the interaction among those individuals."

Oh, brother.