Creatures in the animal kingdom do not generally benefit from practicing monogamy from an evolutionary standpoint. Genes need to be scattered so that the best of the best survive. Most animals instinctively know this and so do not exhibit monogamy. In non-monogamous couplings, the female is equipped to raise young alone, freeing up the males to move on to mate with other females.
For the purpose of evolution then, monogamy does not make a lot of sense. So why are some animals monogamous? Even for their whole lives? What is different about them?
Are Any Species Truly Monogamous?
The truth about monogamy in the animal kingdom is that no species is yet known to be 100% monogamous across the board. There are species more prone to monogamy and individuals who may indeed be 100% monogamous, but there are no animal species that are always monogamous all the time and across all individuals.
Monogamy of any kind is quite rare. Scientists estimate that only 3-5% of all 4,000+ mammal species practice any form of monogamy. On the other hand, in the avian kingdom, it is estimated that as many as 90% of bird species practice monogamy of some kind.
Different Kinds of Monogamy
When speaking about monogamy among animals, there are a couple of distinct ways of defining it. The two most common definitions of monogamy are social monogamy and genetic monogamy.
Social Monogamy
Social monogamy refers to a male choosing a female to mate and raise young with, but not to the exclusion of mating with any other individual. Both males and females may engage in extra-pair copulation or mating. To raise, protect, and feed young, however, the pair stick together and share the responsibilities. These mates may in some rare instances stay together after a mating season, but most will separate after the young are raised and mate with a new individual next season. There is no expectation of fidelity in a socially monogamous coupling and these individuals may be polygamous or polyandrous.
Genetic Monogamy
Genetic, or sexual, monogamy is quite rare. These individuals do practice fidelity, which can be seasonal or for a lifetime. Genetically monogamous pairs will stick with one mate throughout the mating season, focusing more fully on raising and protecting young. This is more commonly found in individual couplings of animals, rather than in species in general.
Reasons Why Some Animals May Be Monogamous
There are a few reasons that an animal may choose monogamy. The first and most obvious is that some species require involvement from both mother and father if the young are going to survive. This is why most birds are socially monogamous. These couples work together to feed babies, protect territory, and fend off danger. It makes sense then that a pair of animals may need to be monogamous for a season until their young are raised.
Another reason monogamy occurs in the animal kingdom is because of a scarcity of mating options or a small and dispersed population. Because of the time it would take to find and mate with more than one individual, it makes more sense to stick with one mate.
In some species, it also requires more time and effort to protect and feed the young in which case monogamy is almost a forced necessity. Additionally, it has been noted that many males are more likely to behave monogamously the more time they spend caring for their young or protecting them from other males.
Monogamy in the Animal Kingdom
Monogamy in the animal kingdom is complex and not well understood in all cases. However, some species are more commonly shown to practice monogamy than others. Wolves practice a kind of monogamy for the sake of establishing and maintaining a hierarchy in a pack. While very rare to see any kind of monogamy in the amphibian, reptile, or fish families, there is a species of frog where the male is responsible for transporting baby tadpoles to pools of water. Because of this care, these frogs are likely to be at least seasonally monogamous.
The prairie vole is an interesting case because they are one of the closest species to practice true monogamy. Male voles tend to mate for life to whichever female they first mated with. They can even become aggressive towards any other females and seem to experience a hormone that rewards monogamous behavior.
Black vultures will go so far as to attack other vultures who participate in extra-pair copulation. Emperor penguins have to devote most of their time and attention to raising a single chick, and so couples generally stick together until their young is on its own. Hornbills, Azara’s Night Monkeys, and Desert Grass Spiders are a few other species that are almost entirely monogamous, season after season.
Conclusion
Any practice of monogamy is rare in the animal kingdom, and true monogamy is even more rare. No species is 100% monogamous. Even so, it is still heartwarming to imagine pairs of swans, wolves, or eagles choosing to stay together for life, bonded as forever partners.
And guess what? For a few individual pairs, it is altogether possible to be true.
