A team of British and Australian researchers compared data across 230 primate species over 75 million years, and found that the threat of infanticide — specifically, the threat of baby primates being killed by unrelated males — likely triggered monogamy.

Since infants are dependent on their mothers throughout childhood, and since female primates typically delay further conception while they are nurturing their young, male competitors may see advantages in doing away with babies that their rivals have sired, said study lead author Christopher Opie, a postdoctoral research fellow in the department of anthropology at the University College London in the United Kingdom.

"For a male who knows he's not the father of an infant, it can pay for him to kill that infant, because then he can make sure the female comes back into ovulation. And he can mate with her," Opie told LiveScience. "It's a way for males to try to increase their genes that are passed into the next generation."