Shared Paternity in South American Tribes Confounds Biologists and Anthropologists

The practice challenges assumptions about gender roles and the evolution of human sexuality

By KIM A. McDONALD

Anaheim, Cal.

Recent studies of multiple fatherhood in indigenous societies in South America are forcing scientists to rethink their notions about the evolutionary roles of female fidelity and male provisioning.

Many biologists and anthropologists had assumed that those behaviors arose as a result of an evolutionary compact between men and women -- one in which fathers provided resources for their mates and children in exchange for knowing that their children are genetically their own.

Reinforced by the belief in Western societies since biblical times that a child can have only one biological father, those gender-specific behaviors -- which presumably enhanced the survival of offspring -- also underpinned many scientists' explanations about the evolution of human sexuality and the division of labor among men and women.

According to that view, the African hominid ancestors of modern humans had a reproductive strategy in which females were only periodically capable of conception and mated with multiple males. Like chimpanzees, the hominids engaged in relatively little food sharing, and the males had minimal roles in providing food for their children.

That reproductive strategy was replaced in modern humans by an arrangement in which men provided for their mates and young in exchange -- according to the theory -- for paternity certainty from women, who are capable of conceiving throughout the year.

"This popular scenario of human evolution makes men providing things for their wives and children the key adaptation that separates us from the other primates," said Kristen Hawkes, head of the anthropology department at the University of Utah. "The thing that's distinctive about our lineage is that men work. Women and children, as a consequence, can consume things that they wouldn't otherwise."

"Concern for paternity certainty is presumed to dominate relations between husbands and wives," said Stephen J. Beckerman, a professor of anthropology at the Pennsylvania State University. "Women are supposed to be naturally inclined to be faithful to a single man. Men are supposed to be inherently jealous and possessive about women."

However, studies that he, Ms. Hawkes, and other researchers have conducted on some of the more than a dozen societies in South America whose members believe that biological fatherhood can be "partible," or shared, are forcing the scientists to rethink that Darwinian view of fatherhood. Many of those scholars met here at the annual meeting of the American Association for the Advancement of Science to discuss the implications of their findings.

"Throughout lowland South America, there is a belief in the partibility of paternity," said Mr. Beckerman at the gathering. "The belief, in essence, is that all of the men who have sex with a woman around the beginning of her pregnancy and all through her pregnancy share the biological paternity of her child. In this view, the fetus is considered to grow by repeated contributions of semen."

The pervasiveness of those beliefs among at least 18 widely separated and distinct cultures in South America, said Mr. Beckerman, suggests that social views about fatherhood are not universal and do not follow the standard picture of the evolution of human sexuality. In fact, he noted, examples of a belief in partible paternity are being discovered outside South America, in indigenous societies in New Guinea, Polynesia, and India.

"All of this calls into question this presumed evolutionary bargain between men and women in which, in effect, female fidelity and guaranteed paternity are the coin with which women pay for resources provided by their mates," he said.

Far from being simply an aberrant challenge to traditional evolutionary thinking, notions of partible paternity may actually be a strategy with real benefits to those societies that recognize multiple fathers.

Mr. Beckerman said his team's studies on the Bari of Venezuela and work by others on the Ache of eastern Paraguay showed that, in both societies, children with multiple fathers were more than twice as likely to survive to their adolescent years as children born to a single father.

"Ethnographic fieldwork suggests that the secondary fathers may have important roles in contributing food to the children and goods to the woman or protection to the children or the woman," said Mr. Beckerman.

What's more, the concept of multiple fatherhood may minimize sexual jealousy, a source of potentially lethal conflict between men. Mr. Beckerman said that one of the more fascinating findings in his work with the Bari, a lowland horticultural society, was that "we never got a man expressing jealousy over his wife taking a lover.

"Presumably, it's because, when that happens, the husband, in effect, has purchased a life-insurance policy. If he dies, then there is some other male who has at least a residual obligation to those children, most of whom probably belong to the husband. So, it's to his benefit to have his wife take a lover or two."

Not all indigenous South American cultures share the same view of multiple fatherhood.

The Canela of Amazonia, in Brazil, for example, actively encourage many sexual partners for pregnant women because they believe that numerous contributions of semen are required to produce a viable fetus.

William H. Crocker, emeritus curator for South American ethnology at the Smithsonian Institution's National Museum of Natural History, in Washington, who has studied the Canela, said this society also believed offspring would grow to resemble the men who contribute the most semen. As a result, he said, "a pregnant woman seeks affairs with men besides her husband, with whom she wants her fetus to be like."

In contrast, the Curripaco Indians, who live in Amazonia on the border of Venezuela and Colombia, believe premarital sex is wrong, but accept the concept of multiple fathers if a mother identifies her lover and that man accepts his role as a father. Often, such women will identify lovers of high social status from desirable villages.

"From their perspective, biological paternity is something that is negotiated," said Paul Valentine, an anthropologist at the University of East London who has been studying the Curripaco since 1981. "This notion of partible paternity can be used in all different kinds of social arrangements such that people can actually choose the strategy that's beneficial to them."

Ms. Hawkes of Utah said that what was clear about all of those societies was that they do not fit the evolutionary paradigm -- that, as humans evolved, males shifted their efforts away from competition with one another for mates to parental nurturing.

Her own studies of the Ache of eastern Paraguay and the Hadza of northern Tanzania, she said, "don't support the notion that men's work is about providing for their kids."

"The products of a man's labors in hunting and collecting honey do not provide more for a man's own wife and children than they do for anybody else. And if a man were really concerned about providing for her, the patterns of his work would be quite different from the ones we see. Male mating competition provides a much more interesting, powerful, more potentially useful set of hypotheses for explaining the evolution of our lineage and, perhaps, for explaining some of the variability we see ethnographically in the modern world."

Robert L. Trivers, a professor of anthropology at Rutgers University who did some of the most influential theoretical work on paternal investment in the 1970s, said in an interview that Ms. Hawkes "makes a compelling initial case for the possibility that, where big game is the usual prey, competition may be for access to women and not parental investment per se." But he suspected that males in such societies were probably making some effort to see that their own children get disproportionately more than other children.

As to why modern Western societies have far-more-rigid rules for mating and fatherhood than do the Bari or Ache, Ms. Hawkes thinks it may be related to the need to minimize the lethal consequences of mating competition in modern society.

"The cost of a fight is much greater among armed humans as a result of their technology," she said. "One of the ways to reduce the cost of that fight is to develop conventions about immediate claims on male mating rights."

Nevertheless, the concept of multiple fathers may be more common in Western society than is believed -- even though it isn't sanctioned or recognized as such.

"You don't have to delve far beneath the surface of the average British woman to find behavior that looks very similar to the sort of behavior of the lowland South American cultures," said R. Robin Baker, a former zoology professor at the University of Manchester, who is now a lecturer and author.

His studies of British women suggest that Western women subconsciously bias conception to their clandestine lovers, rather than their long-term partners, by having sex with their lovers more often during their fertile periods and more often without contraception.

In the responses he received to a survey of 4,000 women, many of whom reported affairs, he said, "the implication is always that, now I've met somebody who can offer me something more genetically than my long-term partner." He added that confidential attempts to check paternity in Europe and North America bear out the fact that fidelity among women is not as common in Western society as one would believe.

"One in 10 children don't belong to their mother's long-term partners, they don't belong to their putative fathers," he said. "The take-home message is that if you compare a British woman with a Bari woman, the difference is one of degree rather than kind. We're dealing with a genetic legacy that is the result of 60 million years of primate evolution."

To Helen E. Fisher, an anthropologist at Rutgers who has spent most of her career studying the evolutionary aspects of mating and pair bonding in humans, partible paternity in South American societies and adultery among Western women come as no surprise.

"Fidelity never was a female reproductive strategy," she said in an interview. "Women have always been adulterous, they've always had clandestine relationships on the side."

Ms. Fisher, author of The First Sex: The Natural Talents of Women and How They Are Changing the World, to be published by Random House next month, said that women as well as men had "evolved a dual reproductive strategy" -- a need to form pair bonds combined with a wandering eye that allows them to take advantage of reproductive opportunities. "In some societies," she added, "the rules are lifted, and it's just more out in the open."

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Section: Research & Publishing

From the issue dated April 9, 1999
Page: A19