When it comes to hookups in the animal world, casual sex is common among chimpanzees. In our closest animal relatives both males and females mate with multiple partners. But when taking the plunge into parenthood, they're more selective than it seems. A study appearing online on January 11, 2017 in the journal Royal Society Open Science reveals that chimps are more likely to reproduce with mates whose genetic makeup differs most from their own. The open-access article is titled “Chimpanzees Breed with Genetically Dissimilar Mates.” Many animals avoid breeding with parents, siblings, and other close relatives, said first author Kara Walker, Ph.D., a postdoctoral Associate in Evolutionary Anthropology at Duke University. But chimpanzees are unusual in that even among nonrelatives and virtual strangers they can tell genetically similar mates from more distant ones. The researchers aren't sure yet exactly how the chimps make this discrimination, but it might be a best guess based on appearance, smell, or sound, said senior author Anne Pusey, Ph.D., Professor of Evolutionary Anthropology at Duke. Researchers took DNA samples from the feces of roughly 150 adult chimpanzees in Gombe National Park, Tanzania, and analyzed eight to eleven variable sites across the genome. From these, they were able to estimate the genetic similarity between every possible male-female pair. In chimpanzees, as in other animals, only some sexual encounters lead to offspring. When the researchers compared pairs that produced infants with those that didn't, they found that females conceived with sires that were less similar to them than the average male. Chimps are somehow able to distinguish degrees of genetic similarity among unfamiliar mates many steps removed from them in their family tree, the study shows.
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