Scientists have long hypothesized that women's biology makes them naturally monogamous and that men are naturally prone to stray and seek multiple sexual partners. This argument is based on the theory that women's more limited opportunities for reproduction (9 months for each pregnancy, with time to wean children in between) and need for help in child-rearing and protection have made them more choosy about their sexual partners, while men's more frequent opportunities for reproduction have compelled them to seek out multiple partners.
Now, anthropologists Stephen Beckerman of Penn State University and William Crocker of the Smithsonian Institution have revealed evidence that contradicts those long-held theories of human reproduction.
In this weekend's annual meeting of the American Association for the Advancement of Science, Beckerman and Crocker reported that studies of several South American cultures have yielded evidence that men's and women's reproductive roles are not determined by biology alone.
For example, the Canela of Amazonian Brazil and several other traditional South American cultures believe that children have many fathers, and that conception occurs only after women have sex with many men. Thus, these cultures do not encourage women to be monogamous, and male sexual jealousy is unnecessary.
Beckerman noted that children of the Bari of Venezuela who had more than one father were more likely to survive than children with just one father. Bari society expects the extra fathers of children to provide support, although the main responsibility is held by a woman's husband.
"All of this calls into question the old evolutionary bargain, in which fidelity is the coin in which women pay for resources from the males," Beckerman said. "You can build a perfectly viable society....[with] male jealousy suppressed, lack of female fidelity -- things that are supposed to be inherent in human nature."
Another anthropologist, Kristen Hawkes of the University of Utah, has done research that flies in the face of theories that men are biologically ingrained to provide resources for their own wives and progeny, and to withhold those resources from others who do not pass on their DNA. In studies of the Hadza of Tanzania and the Ache of Paraguay, Hawkes found that men contributed to their tribes as a whole, and not to their individual families.