Scientists believe they may have discovered the reason most humans, at least in theory, are so wedded to the idea of monogamy, and the answer ain’t “true love.” As a species, we became predominantly monogamous so other humans wouldn’t kill our babies, according to a new study, the Guardian reports. Scientists at University College London wanted to find out why some species practice monogamy and others don’t, so they looked at 230 different species of primates (including us), and found one common thread amongst those who were monogamous: infanticide.

The idea is that males stick close to their female companions to ward off other males, who might kill their offspring so the females will become fertile again. “You do not get monogamy unless you already have infanticide, and you do not get a switch to paternal care if you don’t already have monogamy,” says one of the researchers. Another recent study, at the University of Cambridge, which looked at 2,500 different mammals, found similar results, reports the AFP. However, that study did not look at humans, and the researchers are skeptical that the explanation would apply to us. “Humans are such unusual animals, depending so excessively on culture, which changes so many of the ground rules of evolution,” says one of the researchers.

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