Contemporary discussions of sex differences typically assume that they are determined by society rather than biology. It is society, we hear, that teaches little girls to be feminine and little boys to be masculine; it is society that tells women to respond to babies and men to respond to sports. Reflecting the fashionable idea that male and female roles have been "socially constructed," most commentators speak of gender instead of sex. Because men and women are virtually interchangeable, so the argument goes, men should do an equal share of domestic and childrearing work so that women can compete equally outside the home."

There's one problem with this beguiling vision of androgyny: whatever we might like to believe, as Dr. Steven Rhoads shows, sex distinctions remain a deeply rooted part of human nature. In Taking Sex Differences Seriously, Rhoads assembles scientific evidence demonstrating that these differences are "hardwired" into our biology. They range from the subtle (men get a chemical high from winning, while women get one from nursing) to the profound (women with high testosterone levels are more promiscuous, more competitive and more conflicted about having children than those with average levels.

Pt. 1. Nature matters

1. Androgynous parenting at the frontier
2. Masculinity/femininity

Pt. 2. Men don't get headaches

3. Sex
4. Fatherless families
5. The sexual revolution

Pt. 3. Men want their way

6. Aggression, dominance and competition
7. Sports, aggression and title IX

Pt. 4. Women want their way, too

8. Nurturing the young
9. Day care