The Evolutionary Enigma of Monogamy
A series of seminal studies, into the enigma that is the evolutionary role of monogamy in human beings, has raised serious questions concerning the trait’s advantages.
Specifically, scientists are attempting to comprehend the means by which this form of sexual partnering, in our species, serves to further our existence. From an evolutionary perspective, one would assume monogamous relationships to impose a distinct disadvantage, limiting the number of sexual interactions that human beings have; this, in turn, could limit the number of viable progeny, which could be theoretically much greater if human beings were to adopt polygamous mating rituals.
Similar musings of confusion were reflected in a recent telephone news broadcast, where Dietar Lukas of the University of Cambridge was quoted as saying “Monogamy is a problem,” who went on to justify his opinion. “Why would the male keep to one female?” Indeed, only 9 percent of mammalian species, including wolves and beavers, for example, adhere to these deeply monogamous virtues. Until recently, scientists have struggled to understand exactly why.
According to studies produced by Doctors Lukas and Opie, which were recently published independently on Monday, there could be good reason for, what would appear to be on the surface, this evolutionary aberration.
Lukas and his co-author investigated the mating evolution of 2,545 different species of mammal, traced back to a common ancestor, believed to be in existence 170 million years ago. The results were intriguing in that only on 61 occasions did a mammalian species transition from polygamy to the evolutionary enigma that is monogamy. Spotting this similarity, the pair began drawing further comparisons between the 61 species.
It was theorized that this shift, to a more restricted sociosexual orientation, was provoked by changes in the species’ female populations. Female members of the species would separate, due to significant strife, meaning an attendant changeup in tactics amongst the males was inevitable. Males would stick to one particular area to fend off amorous, sexual rivals and were simply unable to protect other regions of female targets, due to the large distances between them; it is thought this cemented unity between a father and his offspring, whereby males would involve themselves more in duties of care, inspiring an evolution in mating patterns.
Dr. Opie, in his analogous study, published in the Proceedings of the National Academy of Sciences, homed in on a narrower group of species, and were inclined to present different conclusions. Opie investigated 230 primate species, a group renowned for its monogamous ways. It was considered that, once a female was nurturing its new offspring, their capacity to ovulate would become impaired. Therefore, in response, competing males would remove this biological obstruction by engaging in infanticide, so as to promote the female’s ovulation, once more, in the hope they could produce their own offspring. On this basis, Opie argues that monogamy was an evolutionary response, triggered by the potential dangers of infanticide, where males would become partnered to a sexual mate, remaining at their side to protect the young.
When investigating the merits of these studies, a number of eminent scientists have noted the contradictory conclusions. Anthony Di Fiore, an evolutionary anthropologist working for the University of Texas says: “They do seem to be saying the opposite thing… It’s interesting because they use very, very similar methods.” However, despite the studies’ similar investigative approaches, Dr. Opie contends that his study is superior; he highlights that Lukas and Clutton-Brock’s study does not “… use the latest methods, which is a bit of a pity,” a reference to the fact that his peers did not use the same Bayesian probability statistics.
On the other hand, Lukas rejects Opie’s results. “We don’t find any support that infanticide has been important for the evolution of monogamy across mammals,” he argues. Lukas maintains that mammals that engage in infanticide are equally as likely to develop monogamous relations, relative to those that do perform infanticide. And, despite Dr. Opie’s confidence in his research, a number of experts have favored Dr. Lukas’ findings. An impartial source, Jacobus Boomsma of the University of Copenhagen, states that Lukas’ study “…makes perfect sense to me,” whilst evolutionary biologist, Sergey Gavrilets (University of Tennessee), also showed support for Dr. Lukas’ study.
These studies provide interesting insight into the potential reasons behind monogamy and, it is likely, that the situation is far more complex, involving multi-factorial issues that are yet to be fully addressed or understood. In addition, attributing the practices of general mammalian species, and other primates, to human beings has its own flaws. This notion is supported by Bernard Chapais, based at the University of Montreal, who conducted a review into the matter: “The human mating system is extremely flexible.” His results showed that a fraction of human cultures are truly monogamous (17%), with many societies pursuing different types of relationships and marriages. This begs the question, why the variation across different cultures?
Furthermore, it is likely that resources, including food, water and shelter could play another part in a species’ evolutionary inclination towards either polygamy or monogamy, alongside, as choice examples, climatic changes, disease spread and predator type and number.
Overall, the results of these studies are contentious, conflicting with, not only one another, but also the voices of other members of the scientific community. And, from what we’ve seen recently, it is ever-likely that the debate surrounding the evolutionary enigma that is social monogamy will endure for quite some time to come. The two conflicting parties have agreed to share datasets, and are currently determining the basis for their differing results.