Anaheim, Calif. -- Since Biblical times, Westerners have accepted the folk belief that a child has only one biological father, but some non-Western society's folk beliefs hold that every man who contributes sperm during a pregnancy, contributes biologically to the child.
"We now know that only one sperm and one egg contribute to each child," said Dr. Stephen Beckerman, professor of anthropology at Penn State. "But no one knew this scientifically until 1879 when Herman Fol published his microscopic observations. Before this, although Western law and custom assumed that each child had a single biological father, that premise was simply a folk belief. It was just a lucky guess that Western folk biology was correct."
One non-Western belief, called partible paternity, is common among indigenous groups in South America, is also found in New Guinea and may occur on the Indian subcontinent. In a few of these groups, all children have more than one socially accepted father. In others, only some women take extra-marital lovers during pregnancy.
"Partible paternity appears to be quite common in South America and exists in at least 18 groups widely separated in distance and culture in the lowland forests and savannahs," Beckerman told attendees today (Jan. 22) at the annual meeting of the American Association for the Advancement of Science.
"This finding suggests that modern evolutionary scenarios that assume certainty of paternity as a crucial element in the evolution of modern humans from African hominids may be incorrect," he said.
The other elements in these scenarios include sexual division of labor, food sharing, lengthy juvenile dependency and continuous sexual receptivity.
"The existence of partible paternity as a common concept raises serious questions about the presumed evolutionary bargain between men and women. The bargain, that men supply the resources in return for female fidelity and guaranteed paternity, may not exist," said Beckerman, who co-chaired the session, "Partible Paternity: Matings with Multiple Men Leading to Multiple Fathers Per Child."
The behavior of African hominids is usually modeled on that of chimpanzees, with minimal food sharing and minimal sexual division of labor. It is argued that among our ancestors, reproduction involved females who were only periodically capable of conception and, when in heat, mated with multiple males. Males had only minimal investment in the children.
The standard evolutionary scenario argues that these behaviors were replaced by an arrangement where men and women foraged for different resources and males provisioned females and their young in return for paternity certainty from females who were now receptive year round. However, this scenario assumes that the Western folk belief about how children are conceived is universal.
"Not only does the contrary idea of partible paternity exist in many South American groups, but these groups have managed to create societies where families exist and successfully raise children even though they have multiple fathers," said Beckerman. "In fact, there may be an evolutionary benefit to children in having more than one responsible father."
Two previous studies indicate that children with multiple fathers have higher survival rates than children with only one recognized father. The secondary fathers accept a responsibility to the child and may supply meat or fish to the mother for the child, or protect the child from various childhood dangers.
Continued sexual activity during pregnancy may help the child because "courting" gifts of food brought to the mother may help by ensuring good fetal nutrition.
From a biological point of view, multiple, closely spaced sexual episodes may set up a situation where sperm from two or more individuals must compete with each other to fertilize an egg. Evolutionarily, the most fit sperm would win.
"Until recently, the doctrine of one sperm--one fertilization was considered universal, "said Beckerman. "Now the study of partible paternity has attracted considerable attention and we should soon know much more about this alternative view of procreation and how it might affect evolutionary scenarios."
Other participants in this session were Sarah Blaffer Hrdy, University of California -- Davis, a primatologist; R. Robin Baker, author of "Sperm Wars"; and anthropologists Kristen Hawkes, University of Utah; William Crocker, Smithsonian Institution emeritus; and Paul Valentine, University of East London. Crocker and Valentine presented case studies from the South American Lowlands, while Hrdy, Baker and Hawkes dealt with the evolutionary and physiological significance of partible paternity.
EDITORS: Dr. Beckerman may be reached at 814-863-3869 or stv@psu.edu by email.