Monogamy and Its Many Mysteries ; Scientists Look for Clues to What Leads Species to Stay with One Mate

Article excerpt

Two new studies posit theories on why monogamy among primates evolved, but even the scientists admit it's a puzzle that's far from solved.

"Monogamy is a problem," said Dieter Lukas of the University of Cambridge in a news conference by telephone last week. As Dr. Lukas explained to reporters, he and other biologists consider monogamy an evolutionary puzzle.

In 9 percent of all mammal species, males and females will share a common territory for more than one breeding season, and in some cases bond for life. This is a problem -- a scientific one -- because male mammals could theoretically have more offspring by giving up on monogamy and mating with lots of females.

In a new study, Dr. Lukas and his colleague Tim Clutton-Brock suggest that monogamy evolves when females are dispersed, making it hard for a male to travel around and fend off competing males.

On the same day, Kit Opie of University College London and his colleagues published a similar study on primates, which are especially monogamous -- males and females bond in over a quarter of primate species. The London scientists came to a different conclusion: that the threat of infanticide leads males to stick with only one female, protecting her from other males.

Even with the scientific problem far from resolved, research like this inevitably turns us into narcissists. It's all well and good to understand why the gray-handed night monkey became monogamous. But we want to know: What does this say about men and women?

As with all things concerning the human heart, it's complicated.

"The human mating system is extremely flexible," Bernard Chapais of the University of Montreal wrote in a review in Evolutionary Anthropology. Only 17 percent of human cultures are strictly monogamous. The vast majority embrace a mix of marriage types, with some people practicing monogamy and others polygamy. (Most people in these cultures are in monogamous marriages, though.)

There are even some societies where a woman may marry several men. And some men and women have secret relationships that last for years while they're married to other people, a kind of dual monogamy. Same-sex marriages acknowledge commitments that in many cases existed long before they won legal recognition.

Each species faces its own special challenges -- climate, food, or predators -- and certain conditions may favor monogamy despite its drawbacks. …