Are you wondering why you find it so hard to keep monogamy in your relationship? Well, it's not your fault. Your genes don't have it encoded. Or have you seen monogamous apes?
Monogamy is so rare in the animal world that only 3-5 % of the mammals are known to form lifelong pair bonds, like beavers, otters, jackals, foxes, some bats and a few dwarf deer and antelopes.
In fact, strict monogamy is almost inexistent, as creatures that do pair for life, occasionally have flings on the side and some, like the wolf, do not mourn too much a death or a no longer sexually performing partner.
Staying faithful is extremely hard for animals, as the males are programmed to spread their genes and females to get the best genes from the best males for their young.
Instead, monogamy requires an individual to invest its entire reproductive potential on a single mate. This puts lot of pressure on each individual to choose the best mate, which, as in humans, can be tricky.
Three levels of monogamy are distinguished. Sexual monogamy is the practice of having sex only with one mate at a time, for example, pairs that last only one mating season. Social monogamy is when animals form pairs to mate and raise offspring but still have extra-pair copulations. Genetic monogamy occurs when a female's offspring are sired by only one father.
In the last case, there may be no pair bonding (like in fish or frogs). Theoretically (and just theoretically!), for humans, social and sexual monogamy usually go together, but rarely in the animal life. 90 % of all birds are socially monogamous, living and raising young together, but many frequently have extra-conjugal sex.
In one study, female blackbirds that paired with sterilized males were still laying eggs that hatched!...
Animals regarded as symbols of faithfulness, such as gibbons and swans, are now known to cheat, abandon and even "divorce" one other, exactly like in humans. And the famous example of stork fidelity is a bogus! The male is faithful in fact to the nest rather than to the female, and he won't protect her if another female fights with her for the nest.
The very few animals that do stick together are investigated to find the biological basis of fidelity. In the prairie vole, a male vole will prefer to mate exclusively with the first female he loses his virginity to. Far from trying to woo other females, a mated male vole will actually attack them: this is indeed a fanatic lover!
The rare behavior seems to be determined by high levels of certain brain neurotransmitters. One of these, dopamine, is also implicated in drug addiction in humans.
Black vulture has also high ethics: when extra-pair copulation takes place nearby, vultures will attack the philanderer. Vulture pair bonding must be strong, since both parents incubate eggs, each taking a 24-hour shift, and for eight months, the offspring gets fed by both parents.
In a beaver family, there is a strong need for cooperation to maintain their dams and pools, that's why beaver social units are so tight. Thus, monogamy evolved in situations where young need a better cooperation of both parents in raising them.
That's why humans, with their long childhood, form monogamous pairs. But male dikdiks, an African dwarf antelope, are sexually monogamous even if they are not very involved in the raising of the calves. Even so, males have to defend a territory for their families against the intrusion of other dikdiks.
As homosexuality and polygamy are proved to be rampant in the wild, monogamy might be boring for animal sexual lifestyles.