Satoshi Kanazawa

The Scientific Fundamentalist

Boy or girl? What determines the sex of your child? III

Why are women more beautiful than men?

Posted Feb 15, 2009

Physical attractiveness can also bias the sex of your children.  Now, unlike being big and tall or having a tendency toward violence, which increases the reproductive success of only men and not women, being beautiful is good for both men and women.  Beautiful women have greater mating success than less attractive women, and handsome men do better than less attractive men.  But beautiful men and beautiful women tend to do “better” in slightly different ways.

Physically attractive women tend to do well both in long-term and short-term mating; men prefer beautiful women for both.  In contrast, handsome men tend to do well mostly in short-term mating.  Women seek out handsome men for short-term mating (possibly to get good genes for their children by being impregnated by them but then passing the resulting offspring off as that of their unsuspecting husband) but not necessarily for long-term mating, for which other qualities like the man’s resources and status become more important.  In fact, as I explain in a previous series of posts (Why handsome men make bad husbands Part I, II), physically attractive men may not make desirable long-term mates, precisely because other women seek them out for their short-term mating and thus attractive men are less committed to their long-term mates.

So physical attractiveness, while a universally positive quality, contributes even more to women’s reproductive success than to men’s.  The generalized Trivers-Willard hypothesis would therefore predict that physically attractive parents should have more daughters than sons.  Once again, this indeed appears to be the case.  Young Americans who are rated “very attractive” have roughly a 44% chance of having a son for their first child (and thus a 56% chance of having a daughter).  In contrast, everyone else has roughly a 52% chance of having a son (and thus a 48% chance of having a daughter) for their first child.  Being “very attractive” increases the odds of having a daughter by 36% or decreases the odds of having a son by 26%!

The greater tendency of beautiful parents to have more daughters leads to another consequence.  If you look around and rate the men and women around you on their physical attractiveness, you will notice that, whether you are a man or a woman, gay or straight, women on average are objectively more attractive than men.  Why might this be the case?

Thinks about it.  If physical attractiveness is heritable, such that beautiful parents beget beautiful children (and less attractive parents beget similarly less attractive children), and if beautiful parents are more likely to have daughters than others, then it logically follows that, over time, generation after generation, women will become more attractive on average than men.  Once again, studies confirm this implication of the generalized Trivers-Willard hypothesis.  The average level of physical attractiveness among women is significantly higher than the average level of physical attractiveness among men, both in Japan and the United States.  Women are more beautiful than men on average because beautiful parents have significantly more daughters than less beautiful parents.

In my next post, the last one in this series, I will discuss another factor which seems to influence the offspring sex ratio:  Parent’s sociosexual orientation.