Beaty vs. Supply and Demand

From the freakonomics blog

Why Do Beautiful Women Sometimes Marry Unattractive Men?
It may be that the unattractive man has a lot of money, or some other compelling attribute.
But a new study by Satoshi Kanazawa, an evolutionary psychologist at the London School of Economics, suggests it may be a simple supply-and-demand issue: there are more beautiful women in the world than there are handsome men.
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According to this news article, “Selection pressure means when parents have traits they can pass on that are better for boys than for girls, they are more likely to have boys. Such traits include large size, strength and aggression, which might help a man compete for mates. On the other hand, parents with heritable traits that are more advantageous to girls are more likely to have daughters.”

Beauty is apparently just one “female” trait. Kanazawa has done previous research suggesting that nurses, social workers and kindergarten teachers—those with “empathic” traits—also had more daughters than sons. Meanwhile, he found that scientists, mathematicians and engineers are more likely to have sons than daughters.