The Virtues of Promiscuity

"Slutty" behavior is good for the species. That is the conclusion of a new wave of research on the evolutionary drives behind sexuality and parenting.

Women everywhere have been selflessly engaging in trysts outside of matrimony. And they have been doing it for a good long time and for excellent reasons. Anthropologists say female promiscuity binds communities closer together and improves the gene pool.

More than 20 tribal societies accept the principle that a child could, and ideally ought to, have more than one father, according to Pennsylvania anthropologist Stephen Beckerman. "As one looks, it begins to crop up in a lot of places," says Beckerman, who has reviewed dozens of reports on tribes from South America, New Guinea, Polynesia and India as co-editor of the newly released book, "Cultures of Multiple Fathers."

Less than 50 years ago, Canela women, who live in Amazonian Brazil, enjoyed the delights of as many as 40 men one after another in festive rituals. When it was time to have a child, they'd select their favorite dozen or so lovers to help their husband with the all-important task. Even today, when the dalliances of married Barí ladies in Columbia and Venezuela result in a child, they proudly announce the long list of probable fathers.

In other words, the much-touted evolutionary bargain of female fidelity for food -- trotted out by evolutionary psychologists with maddening regularity -- just doesn't hold up.

"This model of the death-do-us-part, missionary-position couple is just a tiny part of human history," says anthropologist Kristen Hawkes, who has spent years studying the foraging habits of the Aché, a Paraguayan people, and the North Tanzanaian tribe Hadza, who also celebrate a rich love life. "The patterns of human sexuality are so much more variable."

American college students still learn that human society is based on the age-old economic contract between the sexes: Men hunt and women raise children. Fathers provide meat for the family, and in exchange, moms offer fidelity and the guarantee of paternity. While men -- who produce millions of sperm -- are inveterate philanderers, gals, stuck with relatively few eggs that require a significant investment, tend to be choosy and coy. Men therefore are biologically prone to spreading their seed far and wide, while women focus on finding the perfect pop.

"This evidence is a real thumb in the eye for that view," says Beckerman.

Anthropologists claim, good judgment aside, evolution has nudged women a bit toward promiscuity and sexual adventure. In all well-studied primates, females exhibit a polyandrous tendency when given the opportunity to stray. Some who cheat appear to be more fertile, and the offspring of most are more likely to survive. Fooling around appears to have helped our ancestral mothers equip their little ones for success -- the sexual equivalent of reading to them every night or enrolling them in the after-school chess club.

"Women tend to do things that are associated with the welfare of their kids," Hawkes says.

In contrast to the sex-for-food model, multiple and various sexual pairings have little to do with adding to the larder in the groups Hawkes studies. The average Hadza hunter, who can only bring in a big game carcass once a month, has to share his kill with everyone. His wife and kids just have to get in line. Extra mates add a little genetic diversity. But Hawkes says females likely hook up with multiple males for safety more than any other benefit -- a mother's strong emotional bonds with more than one fellow provide an extra protective hand in times of danger.

An economic incentive promotes female infidelity in Barí society. All of the Barí children who had more than one father were more likely to survive into adulthood, fortified by small gifts of fish and game in times of scarcity. Multiple dads also help ensure a child's health. Since a father is necessary to blow tobacco smoke over the little one's body if he or she falls ill, the more potential volunteers the better.