Monogamy may sound sweet, but why it evolved isn't

Associated Press
FILE - This Aug. 29, 2008 file photo shows a yellow-cheeked crested gibbon sitting in a cage at Cambodia's Phnom Tamau Zoo in Takeo province, south of Phnom Penh, Cambodia. Two different studies looking at why monogamy evolved in some species, pointed at separate reasons. Gibbons are one of the monogamous species among the world’s mammals and chimpanzees are at the other end of the spectrum and wildly promiscuous, said anthropology researcher Kit Opie of University College London, an author of one of the studies. (AP Photo/Heng Sinith, File)

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WASHINGTON (AP) — Only a few species of mammals are monogamous, and now dueling scientific teams think they've figured out why they got that way. But their answers aren't exactly romantic.

The answers aren't even the same.



So it's not about romance, said researcher Dieter Lukas of the University of Cambridge, lead author of the mammals study. "It's just really the best he can do."



"Romance obviously came after" monogamy, said Christopher "Kit" Opie, an anthropology researcher at the University College London, who was the lead author of the primate study


Researchers said they hesitated to apply their conclusions to humans, and they acknowledged that their results aren't exactly the stuff of Valentine's Day.

Less than 9 percent of mammal species pair up socially.




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.



"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.


Opie agreed, saying: "Strict monogamy, such as (with) the gibbons, is not what humans do."



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