Why We Love Read Free

with a spouse? Neuroscientist Tom Insel and his colleagues discovered in these animals an extra bit of DNA in the gene that controls for the distribution of vasopressin receptors in the brain, a bit of DNA not present in their promiscuous, asocial cousins, montane voles. These scientists took this tiny piece of DNA out of prairie voles and inserted it into some highly promiscuous male mice. Sure enough, these mice began to form close monogamous relationships with particular females. 4
    Humans have a similar gene that codes for the activities of vasopressin. And some people (but not all) carry this same extra bit of DNA on this gene. 5 Someday we will know exactly what this genetic region does in people and why some carry it and others don’t. For the moment we can say this: long, long ago humanity must have needed to pair up to rear their young—because at least one gene that codes for monogamous behaviors is embedded in our DNA.
    “Two are better than one,” the Bible says. 6 I think our forebears understood this aphorism more than 3.5 million years ago.
    Evolution of Divorce
    But I don’t see why these primordial pair-bonds needed to be permanent. Everywhere in the world where people are permitted to divorce (and economically can divorce), many do. If you ask them why they terminate a union, each gives a different reason. Yet human parting has some patterns—and some of this blueprint appears to have evolved in the cradle of humankind.
    I arrived at this conclusion while I was gathering divorce data on fifty-eight diverse human societies recorded in the Demographic Yearbooks of the United Nations. 7 I found several surprising worldwide patterns to human separation. There were many exceptions, of course. But as a rule, couples around the world who divorced, tended to part during and around the fourth year of marriage, in their middle twenties and/or with a single dependent child.
    At first these patterns were meaningless to me. But as I read about the mating habits of other creatures, I began to see some uncanny parallels.
    Only 3 percent of mammals pair up to rear their young; humans are among them; but this habit only occurs under special circumstances. Among these: female mammals form a pair-bond when they cannot rear their infants by themselves.
    Such are foxes. The dog fox and the vixen form a pair-bond in mid-February, build several dens, and rear their kits together. They do this because the female bears as many as five exceedingly helpless kits; they are born blind and deaf. And the female’s milk is so thin that she must remain in the den almost constantly to feed her young. She will starve unless someone feeds her. So she and a “special” friend form a pair-bond and rear their young together. As the kits wander from the den in high summer, however, parents depart—separately. Their work is done. Next year the couple may reunite; more likely each will take a different mate.
    Serial monogamy is common among our feathered friends. The robins that grace our parks each spring pair up for the breeding season. They, too, must divide their duties. Someone must incubate the eggs, then protect the chicks; the other must provide dinner for the family. Successful couples raise several broods. But when the last of the fledglings wing away, parents part. Next year, many will take new spouses.
    So, in those species that pair up to rear their babies, many remain together only long enough to raise the young through infancy.
    This principle also seems to apply to people. In traditional societies, the lifeway of habitual exercise, a lean diet, and low body weight coupled with the habit of nursing an infant for extended periods around the clock inhibits regular ovulation for several years after childbirth. Among these societies are the !Kung Bushmen of southern Africa, the Australian Aborigines, the Gainj of New Guinea, the Yanomamo of Amazonia, and the Netsilik Eskimos; women in these cultures tend to bear their young about