Partible paternity is the idea that more than one father can contribute genetic material to a child. In fact, the idea that all men who sleep with the child's mother may contribute biological materials to the child and share paternal responsibility.
In Western thought, single paternity has been standard for thousands of years, but it was only a little more than a 100 years ago that scientists showed that one sperm fertilized one egg, says Dr. Stephen Beckerman, associate professor of anthropology at Penn State. Science had proven the Western folk belief that each child had one father, and anthropologists, forming the "standard model" of paternity, relied on the One Sperm, One Fertilization Doctrine and assumed that it is accepted in all cultures by all fathers.
"These views of universal human nature, as well as the male-female bargain behind the Standard Model of Human Evolution, are called into question by decades of ethnographic research among tribal peoples in lowland South America," say Beckerman and Dr. Paul Valentine, senior lecturer in anthropology, University of East London, in the introduction to their new book "Cultures of Multiple Fathers: The Theory and Practice of Partible Paternity in Lowland South America" (University Press of Florida, 2002).
The male-female bargain is that a man will provide food and shelter for a woman and her children if he can be assured that the children are biologically his. However, in South American cultures like the Bari, Tapirape and Ache, multiple fathers take responsibility for the same children, sometimes to the benefit of children and mothers. Among some groups, it is assumed that more than one father or at least more than one insemination, is required to form a fetus.
"The frequency and distribution of the idea of partible paternity show that the doctrine is common throughout an entire continent and that it is found among peoples whose cultural traditions diverged millennia ago," says Beckerman. "These people live thousands of miles apart, speak unrelated languages and have not been in contact for centuries."
In some of these societies, nearly all children have multiple fathers. In others, while partible paternity is accepted, socially the child has only one father. However, in the middle are groups where some children do have multiple fathers and some do not. In this case, the children can be compared to see how having more than one father benefits the children.
Among the Bari of Venezuela, many women, but not all, take lovers during their pregnancy. They later identify these men as secondary fathers of their children. In this case, "possession of a secondary father was associated with a heightened probability that a pregnancy would eventually produce an adult Bari individual," says Beckerman. The researchers found that the benefit was most pronounced in the number of pregnancies that actually came to term, probably due to the additions to the mother's diet of gifts of fish and game from the lover. To a lessor extent, secondary fathers also contributed to the survival of their children after they were born. Surprisingly, it appeared that brothers and sisters of children with secondary fathers were detrimentally affected by a sibling's secondary father, but further investigation showed that mothers whose single paternity children had died, were more likely to take a lover in subsequent pregnancies, somewhat increasing the rate of dead siblings without secondary fathers.
The range of cultural approaches to single or partible paternity can be looked at as a competition of the reproductive rights of men and women and how society will be shaped.
"In small egalitarian horticultural societies, women's reproductive interests are best served if mate choice is a non-binding, female decision; if a network of multiple females to aid or substitute for a woman in her mothering responsibilities exists; if multiple men support a woman and her children; and if a woman is shielded from the effects of male sexual jealousy," Beckerman says.
Men's reproductive interests are best served by male control over female sexual behavior. To do this, men must chose the spouses either for themselves or their children, marriage must be for life, female promiscuity is forbidden, and support networks of women for women are disrupted or male support by other than a husband and his family is forbidden.
"It is obvious that neither sex can fully win this contest," says Beckerman.
In cultures where women chose their mates, women have broad sexual freedom and partible paternity is accepted, women clearly have the upper hand. In societies where women's sexual activity is controlled by men, marriage is exclusive and male sexual jealousy is a constant threat, men have the upper hand. In between is a full range of combinations and options, all represented in the varying South American cultures depicted in the book.