Fewer than 10 percent of all mammal species are monogamous. In fact, biologists have long disagreed over why monogamy exists at all. That's the subject of two studies published this week — and they come to different conclusions.The competing theories are about food scarcity and infanticide.
Animals that leave the most offspring win the race to spread their genes and to perpetuate their lineage. So for most mammals, males have a simple strategy: Mate with as many females as possible.
"Monogamy is a problem," says Dieter Lukas, a biologist at Cambridge University. "Why should a male keep to one female?"
This is interesting, but it does not tell us anything about humans. Even if it did tell us about human instincts, it would not tell us what marriage law ought to be. For example, if scientists discovered that we had some sort of mammalian infanticide gene, that would not be a good reason to legalize infanticide. We have written laws for civilized society, and no other animals have that.