The concept of monogamy is one that is upheld and valued amongst a vast majority of human populations and cultures, yet only about 5% of mammals actually adopt the principle. In terms of genetics, committing to a single partner for life is actually seen as disadvantageous and costly as essentially one would be placing their entire reproductive investment into the capabilities of a single mate. This makes potential mate selection a highly pressurised decision and the search for the ‘perfect partner’ is often regarded as an arduous and somewhat impossible task.
A possible explanation for why humans have generally adapted towards the monogamous lifestyle is that from an evolutionary perspective, young raised with the involvement of both parents typically displayed a greater chance of survival. Compared to the majority of the animal kingdom, human children have one of the longest maturation periods and so monogamy was adopted.
Despite the very small minority of mammals that display monogamy, the prairie vole is renowned for being one of the most faithfully devoted animal species. They are also regarded as the model organism for scientists studying monogamous animal behaviours. When a male vole mates for the first time, he forms an everlasting bond with his female companion that is prolonged for the entirety of his lifespan. In fact, the male vole’s devotion to his female mate is so unconditional that he will pay no attention to the courting behaviours of other females and will sometimes go as far as to attack those who pose a threat to his stable and intimate relationship. The otter, a close relative of the prairie vole, has also adopted the monogamous lifestyle and can sometimes be seen holding hands with their mate whilst asleep to prevent getting separated from one another by currents and rapids.
Whilst monogamy has withheld removal through natural selection, the disadvantages associated with it can help explain why partners tend to stray or turn unfaithful. Both sexes are inherently programmed by their genetics to maximise their chances of successfully conceiving viable offspring that can continue their lineage. Should any aspect of their mate stand to jeopardise these prospects, then the intention to move on to another mate can be described as ‘instinctive’.
Unlike mammals, the majority of bird species are classed as monogamous with approximately 95% falling under the category. A recent study conducted by the University of Washington reported a Magellanic penguin couple that had stayed together for 16 years. Out of a colony of tens of thousands of other penguins, the pair would reunite with one another exclusively in anticipation for the next breeding season. In contrast swan couples, often portrayed as a classic symbol of love, are known to stray elsewhere and ‘divorce’ one another following unsuccessful mating despite being classed as a monogamous species.
Whilst there are examples of truly faithful animal couples, it is also worth noting that the decision to adhere to monogamy is ultimately down to the individual and their unique genetic composition. A good comparison would be our closest relative the bonobo, with whom we share ~99% of our DNA with, a highly promiscuous species which engages in more sexual liaisons than any other primate.