WASHINGTON -- 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.
One team looked just at primates, the animal group that includes apes and monkeys. The researchers said the exclusive pairing of a male and a female evolved as a way to let fathers defend their young against being killed by other males.
The other scientific team got a different answer after examining about 2,000 species of nonhuman mammals. They concluded that mammals became monogamous because females had spread out geographically, and so males had to stick close by to fend off the competition.
So it's not about romance, said researcher Dieter Lukas of the University of Cambridge, author of the mammals study. "It's just really the best he can do."
Both teams discounted a long-standing explanation for monogamy, that it provides two parents rather than one for rearing offspring. That's just a side benefit, they said.
"Romance obviously came after" monogamy, said Christopher "Kit" Opie, an anthropology researcher at the University College London, the lead author of the primate study.
The studies were published online today in the journals Science and the Proceedings of the National Academy of Sciences. The mammal paper in Science excluded humans, while the primate analysis in PNAS counted people both as monogamous and not, because that differs around the world.
Less than 9 percent of mammal species pair up socially.
Among primates, about 25 percent of the species are socially monogamous, Opie said. Some, like gibbons, are highly monogamous while others, like chimps, are on the other end of the spectrum, Opie said. -- AP