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A pair of researchers, one with the University of California, the other with the Max Planck Institute for Evolutionary Anthropology, has found that women in an East African community benefit from multiple marriages while the men seem to suffer. In their paper published in Proceedings of the Royal Society B, Monique Mulder and Cody Ross describe their study of people living in Pimbwe, a community in a western part of Tanzania, and what they learned from them.

British geneticist and botanist Angus John Bateman proposed in 1948 that variability in reproductive success is greater in males than females. Since that time, Bateman's principles, as they have been named, have become somewhat of a standard that describes variability of partnerships in human sexual relations. In effect, they suggest that because men are able to spread their seed around indiscriminately, they more effectively reproduce if they have multiple partners. Women, on the other hand, women, bound by time and the number of children they can carry, are more likely to fare better in fewer and longer sexual relationships. In this new effort, the researchers have tested those principles in a real human population and report evidence that contradicts them.

Mulder and Ross analyzed data covering a 20-year period for approximately 2000 people living in Pimbwe. The data covered marriages, divorces, births and deaths for virtually everyone living in the small community. The researchers found something surprising: women who married multiple times had more surviving children than women who married fewer times. Also surprising was that men who married multiple times had fewer surviving children than did men who married fewer times.

The researchers note that swapping partners is quite common in Pimbwe, and marriage is a rather loose term—either partner is free to leave at any time. They report that they were surprised by their results, as they contradict at least two of Bateman's principles. They also acknowledge that they were not able to explain why there were differences from the expected norm in Pimbwe. They further suggest their findings challenge evolutionary stereotypes, and point out that female mating strategies are clearly more complex than has been suggested by prior studies.

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More information: Monique Borgerhoff Mulder et al. Unpacking mating success and testing Bateman's principles in a human population, Proceedings of the Royal Society B: Biological Sciences (2019). Monique Borgerhoff Mulder et al. Unpacking mating success and testing Bateman's principles in a human population,(2019). DOI: 10.1098/rspb.2019.1516 Press release Journal information: Proceedings of the Royal Society B

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