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Why? Because primates breast-feed their offspring for a long time, even for years, and competing males kill off infants if the dad doesn't stick around to fight them off. But Tim Clutton-Brock, a zoology professor who wrote the all-mammal study in Science with Lukas, said their research saw absolutely no evidence of infanticide spiking before monogamy. Instead, Clutton-Brock and Lukas found that in nearly every case, solitary females came before social monogamy. Those females had spread out to monopolize food like fruit that was of better quality but harder to find. That made it harder for males to keep other males from inseminating the females, Lukas said. "Males cannot successfully defend more than one female," Lukas said. So they stick around and monogamy occurs. Frans de Waal of Emory University, who wasn't part of either team, said he thought the Opie infanticide paper offered quantifiable support for that theory, but he wasn't sold completely. Another independent expert, Sue Carter of the University of Illinois at Chicago, looks at the biochemistry of monogamy in individual species, zeroing on two hormones. And those hormones "are associated with protection, defensive behavior," so they could fit with either conclusion, she said. Both teams did agree that they wouldn't quite put humans in the monogamous category. Clutton-Brock said his study found species that are monogamous have fewer physical differences between the genders. They are about the same size, live about as long. That's not humans. Opie agreed, saying: "Strict monogamy, such as (with) the gibbons, is not what humans do." ___ Online: Proceedings of the National Academy of Sciences: The journal Science: http://www.sciencemag.org/
http://www.pnas.org/
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