Growing up with too many sisters makes men less sexy--study

According to the researchers, the ratio of male and female siblings within a family has the potential to influence the sexual behavior, if not the sexuality, of an outnumbered boy in the family.

Researchers studied rat litters to arrive at this conclusion and stated that genes might determine one’s behavior and personality but environment, in which one is born and raised in, plays an important role in “shaping it.”

Lead author, a professor of Zoology and Psychology at the University of Texas at Austin, David Crews, said while commenting on the study results in a press statement:

"We found that males raised in a female-biased litter exhibited less mounting than males raised in either a male-biased litter or one with an equal sex ratio, and were less attractive to sexually receptive females, eliciting fewer soliciting behaviors. The reported differences in sexual behavior did not vary with the quality of maternal behavior or with sexual experience in adulthood."

Research study findings
Researchers experimented with new born rats by separating them in three groups, male dominated, female dominated, and equally mixed.

Then they tested to see how males from all three categories will behave with sexy female rats when they have grown up.

For this, researchers re-arranged the sex ratios of rat litters in all three groups and they found that the male rats reared with many sisters spent less time chasing after or mating with female rats compared to male rats brought up either in male dominated or in an equally divided litter.

Researchers believe, not just male rats brought up in female dominated group showed less interest in impressing the other sex but, in weird way, even female rats were found to be less than eager to invite these males for mating.

"If they (females) want to mate with a male, they'll do a move called a dart-hop. The females did this less when they were with a male rat that had grown up in a female-biased litter," said Crews.

Crews noted that the study findings might apply to humans also, as rats share most of the similarity with human DNA.

Structure of family plays role
Crews added, the experiment reveals one very important aspect of life that “families are important” and plays major role in shaping up an individual’s personality.

Another major factor that has the ability to influence and shape up one’s personality is “how many brothers and sisters you have, and the interaction among those individuals.”

"Families are particularly important in shaping personalities. The environment where you were raised doesn't determine personality, but it helps to shape it," he concluded.

The study findings appeared in the October issue of the journal 'Psychological Science.'