How monogamous are chimpanzees?

 

Not at all; they’re quite promiscuous. Male chimpanzees compete for females and copulate with as many as possible. Females copulate with multiple males not only to conceive young but also as a sexual favor that’s repaid by more favorable treatment from males, such as food sharing and protection. Such female behavior creates a state of “paternity confusion” in which males are more caring toward females they’ve copulated with, and toward the young of those females, because they recognize that they might be the father of those offspring (“Mama’s baby, daddy’s maybe”). Intense competition among males is why they have such big testicles—more sperm means a better chance of siring young. Get a load of this boy’s “boys.” (He looks pretty pleased with himself, doesn’t he?)

Gorillas are much less promiscuous, and one dominant silverback has uncontested dominion over a harem of females. With so little competition, they don’t need to produce as much sperm to ensure their paternity, so they have little bitty testicles relative to their body size, despite being much larger in body than chimps. See?—you can hardly see them.

But even the gorillas aren’t monogamous; they’re polygynous (one male to multiple females).

Other than humans, the most nearly monogamous apes are gibbons, which form one-on-one pair bonds and usually mate for life. But like humans, even they mess around a bit (extrapair copulations) and sometimes divorce.