The Rise and Fall of Sexual Promiscuity
The Rise and Fall of Sexual Promiscuity
Sleeping around once had its benefits, but turns out women may have given up better fertility for better security.
Long before match.com and The Bachelor—even before yentas and oracles—there was the primal jungle, and finding a mate was messy business. Violence and hierarchy ruled the day. Alpha males got the girls; lesser competitors did not. Evolutionary biologists have long tried to trace the human path from combat to courtship: When did we crude animals trade polygamy and paternal absenteeism for “I do” and BabyBjörn?
A new study from Sergey Gavrilets, professor of ecology, biology, and mathematics at the University of Tennessee-Knoxville, reviews the current evidence and offers an intriguing hypothesis. The transition from “promiscuity to pair-bonding,” Gavrilets writes in the journal PNAS, occurred only when lesser male hominids, realizing their physical inferiority, adopted a “provider” role in partnerships, and female hominids, in turn, began to show fidelity to these partners. (Others have postulated that the rise of agriculture helped smooth the way for the transition.) The role of female choice is not often considered in evolutionary biology, but if Gavrilets’ models are correct, it may be integral to explaining our past.
Scientists have also long debated the origins of pair-bonding, not because its advantages are in dispute, but because, according to evolutionary logic, it ought never to have happened.
Many species are indeed better off, Gavrilets explains, when their males live cooperatively in societies, helping raise families, rather than warring over mates and leaving their offspring fatherless. But males face a “social dilemma” when it comes to spreading their genes: if they choose to spend their energy providing for—rather than fighting for—mates, other males may cheat and “free ride” on their largesse. (So-called “free rider” problems show up not just in biology, but in every corner of economics, psychology, and environmental policy.) Of all the theories that explain why cooperation (i.e. pair-bonding) replaced competition (i.e. promiscuity) among our ancestors, Gavrilets argues, none account for this social dilemma.
