Science has come a long way since then, as Dr. Hrdy notes in her introduction to a recent issue ofPhilosophical Transactions of the Royal Society devoted entirely to the topic of female aggression. She credits the “stunning” amount of new evidence partly to better research techniques and partly to the entry of so many women into scientific fields once dominated by men.

The existence of female competition may seem obvious to anyone who has been in a high-school cafeteria or a singles bar, but analyzing it has been difficult because it tends be more subtle and indirect (and a lot less violent) than the male variety. Now that researchers have been looking more closely, they say that this “intrasexual competition” is the most important factor explaining the pressures that young women feel to meet standards of sexual conduct and physical appearance.

The old doubts about female competitiveness derived partly from an evolutionary analysis of the reproductive odds in ancient polygynoussocieties in which some men were left single because dominant males had multiple wives. So men had to compete to have a chance of reproducing, whereas virtually all women were assured of it.