- Sexual monogamy is the practice of having sex only with one mate at a time.
- Social monogamy is when animals form pairs to mate and raise offspring but still have flings — or "extra-pair copulations" in science lingo — on the side.
- Genetic monogamy is used when DNA tests can confirm that a female's offspring were sired by only one father.
For humans, social and sexual monogamy usually go together, but this isn't always the case with other animals. For example, an estimated 90 percent of all birds are socially monogamous, living and raising young together, but many frequently have sex with other partners. One famous experiment found that female blackbirds paired with sterilized males were still laying eggs that hatched. The females couldn't chirp their way out of that one.
Also, animals once regarded as exemplars of faithfulness, such as gibbons and swans, are now known to cheat, abandon and even "divorce" one other, just like humans
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