All In The Family

What's going on with relationships?

Recently reported: 37% of U.S. births are out of wedlock. Not to be outdone, in France 59% of women have their first baby out of wedlock. This is not due to an increase in teenage pregnancy rates, but due to women choosing to have babies in cohabitation with the father rather than in marriage.

Is cohabitation preferred because divorce is so likely?

Divorce rates rose in the sexual liberation of the 1960s and 1970s, hovered close to 50%, and began to decline in the 1990s. These days women without college education have a much higher risk of divorce than those with a degree.

But since 1980, the two groups have taken diverging paths. Women without undergraduate degrees have remained at about the same rate, their risk of divorce or separation within the first 10 years of marriage hovering at around 35 percent. But for college graduates, the divorce rate in the first 10 years of marriage has plummeted to just over 16 percent of those married between 1990 and 1994 from 27 percent of those married between 1975 and 1979. -- NY Times

These trends beg the question: how are humans supposed to have relationships? Do we need a college degree?

In The Ancestor's Tale: A Pilgrimage to the Dawn of Evolution, Richard Dawkins presents a graph (p. 210) of the relationship between testis mass and body mass for various primates. In species like chimpanzees where females mate with many males, there is sperm competition. As the graph shows, chimpanzee males tend to have a proportionately higher testis to body mass ratio, indicating that they produce as much sperm as they can to compete for egg insemination. Monogamous gibbon males, on the other hand, have a smaller testis to body mass ratio because their sperm does not have to compete for egg entry.

As far as primates go, human males fall in the camp of smaller testis to body mass ratio. This suggests that humans tend not to be promiscuous (many males mating with a female). It does not clarify, though, whether males have harems or act monogamously.

Frans De Waal compares human relationship behavior to our two evolutionarily closest kin, the chimpanzee and the bonobo in Our Inner Ape. De Waal doesn't claim that we should act like chimps or bonobos, but comparisons of sexual behavior between the species are enlightening. Both chimps and bonobos are promiscuous, but chimps have a patriarchal (alpha male) society while bonobos have a matriarchal society. If you compare population of humans, chimps, and bonobos, human sexual and social behavior is strikingly successful.

What do humans do differently than other primates?

Alpha male chimps dominate the genetic outcomes of their populations. In fact, new alpha males are known to kill children from predecessor alpha males (this behavior occurs in other species that have alpha males) to enhance their genetic dominance. Bonobo females avoid infanticide by having sex with lots of males. Bonobos are very promiscuous indeed, with sexual activity throughout the day between all members (heterosexual and homosexual). Since the males have no idea who the father is, they cannot kill children for the sake of genetic dominance.

Humans have a different twist. Human males have a good idea who their offspring are. Unlike chimps, human males don't commit infanticide purely for the sake of genetic dominance (though in some societies they have been known to kill first-born females for a variety of seemingly economic reasons). De Waal posits that human females avoid infancticide by including males in the childrearing so that males protect their own children and probably the children of their clan. This may explain a good deal of human social behavior including common institutions like marriage.

Do we need marriage?

An emerging idea is that, with a population of six billion humans, maybe humans are simply adapting to a different environment. Survival of the species depends more on our ability to control our collective impact on the planet than it does on our ability to reproduce.

Modern society turns the table on primal human needs. The likelihood and expense of divorce may explain why more women prefer cohabitation to marriage. Cohabitation achieves the goal of including males in childrearing with a better expected economic outcome. In addition, societies that outlaw infanticide have removed an important reason for females to enlist males in childrearing in the first place. If the father disappears or fails to participate in childrearing, laws protect the life of the child anyway.

The next step in human relationships? Sexual Consent Forms , anyone? (Tip of the hat to Dennis on this video).