University Park, Pa. -- Among the Bari of Venezuela, women who are promiscuous during pregnancy increase the survivorship of the children they are carrying, but their dalliances do little for other children in the family, according to Penn State anthropologists.
"We thought that the support of additional fathers would improve the survival of all the children," says Dr. Stephen Beckerman, professor of anthropology in the College of the Liberal Arts. "But, that does not turn out to be the case, only those children with secondary fathers benefited."
Partible paternity, the belief that a child can have several biological fathers, should increase survivorship among children. This works because manioc, a starchy tuber with a low nutrient density, is the basis of the Bari diet, supplemented by fish and meat. A manioc diet is generally sufficient for adults, but children may have difficulty eating sufficient manioc to obtain adequate nutrition because of their smaller stomachs. Animal protein, supplied by male relatives, wards off protein-calorie and micronutrient malnutrition.
"A high death rate, caused by disease and chronic war -- attempts by landowners, homesteaders and oil companies to exterminate the Bari -- produced frequent widows and orphans, which impacts children's health," says Beckerman.
"Bari belief is that all the men who have intercourse with a woman during her pregnancy share the biological fatherhood of her child. The woman's husband, if he cohabited with her during pregnancy, is usually considered the primary biological father. The lovers are secondary fathers."
The Bari Partible Paternity Project investigated the occurrence and consequences of secondary fatherhood among the Bari to determine if "paternity confusion" -- the biological label of the belief in the outcome of partible paternity -- was adaptive for present-day Bari women. Using life history interviews with elderly Bari, the researchers established that before peaceful contact in 1960, most Bari women took lovers during at least one of their pregnancies.
"In a majority of these cases, the married women said they took a lover only after they were pregnant, and that their husbands were usually aware of the lovers," says Beckerman. "There is no evidence that the husbands objected."
After the birth, mothers named the men with whom they had intercourse during the pregnancy, and one of the women attending would announce to each of the men that he had a child. The secondary fathers had obligations to the child; specifically, they were to provide fish and game to the child. In a recent issue of the journal Current Anthropology, the researchers reported that adherence to this obligation was variable. Some Bari reported that their secondary fathers never supplied meat, while others regularly brought food.
When some fathers brought large amounts of food, the children were encouraged to share the food with their siblings. If the secondary father brought only a small amount of food, a fish or a squirrel, the child usually consumed the food alone.
The study included 74 postreproductive women who provided secondary fathers for at least one of their children and 37 women who did not. These women had 897 pregnancies. The researchers investigated the survivorship to age 15 of children with and without secondary fathers.
Of the 897 known pregnancies, 65 children have not yet reached age 15 and 10 children died at unknown ages. Five hundred and sixty of the remaining 822 children reached age 15, which produced an overall survivorship of 68 percent.
Survivorship of children with secondary fathers was 80 percent, while that of children with only primary fathers was 64 percent. "These numbers indicate that promiscuity during a single pregnancy increases the survivorship of the resulting child," says Beckerman. "We assume that the increase in survivability is related to secondary fathers' providing food."
The researchers then divided the group into those with secondary fathers, those with siblings with secondary fathers and those without secondary fathers in the family. Siblings of those with secondary fathers had a survivorship rate of 61 percent while those without secondary fathers in the family had a rate of 69 percent.
"Those with secondary fathers had a two and a half times better chance of surviving than their siblings without secondary fathers," said Beckerman. "We had hypothesized that siblings of children with secondary fathers would benefit from secondary father's gifts of food, because gifts to small children are usually handed over to the mother who distributes it among all her children.
"We now suspect that children with secondary fathers do not benefit primarily from the large amounts of protein distributed in times of abundance, but rather, from small food gifts given privately to children during times of scarcity."
The research team consisted of Beckerman; Roberto Lizarralde, Facultad de Ciencias Economicas y Sociales, Universidad Central de Venzuela; Carol Ballew and Sissel Shroeder, Penn State Ph.D. recipients in anthropology; Christina Fingelton, Angela Garrison and Helen Smith, all former Penn State undergraduates in anthropology.
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