Social Monogamy in Primates

In an evolutionary stand point, the goal of all organisms is to reproduce. Mammals adopt a k-selection strategy to accomplish this goal where an investment is placed in the care of the young until a certain level of maturation is achieved. However, interactions between mammals range in different types of relationships. Most will display promiscuous relationships, where a male and a female will only associate for the act of mating and will separate after. However, why does monogamy appear in mammals then? Monogamous mammalian relationships are believe to be based on the increased dependency due to the long period of intense developmental care and gene assurance. Developmental care is important to the survivability of the young and ability to thrive there on after. However, the longer the period is for lactation and developmental care, the more vulnerable the mother is. The mother must provide for food and protection, leaving her more exposed. Paternal care allows for this job to become split, creating a more stable and symbiotic relationship per “family unit.” Monogamous relationships will also reduce the chances of the offspring being from another male. This assures the male that the offspring is in fact his, allowing both the mother and father to achieve their biological destiny.

In Male infanticide leads to social monogamy in primates, primates are believed to have evolve into social monogamy due to male infanticide. In the article, there are three plausible hypothesis for the appearance of monogamy – parental care, mate guarding, and infanticide risk. Using the likelihood-based phylogenetic comparative methods in a Bayesian framework, Opie et al examine each of these three hypothesis to test their correlated evolution between mating system, suggesting data that will correlate to indicate social monogamy. And though all three are indeed present in social monogamous relationships, only male infanticide is believed to have preceded it. It was the only trait tested in primates to have consistently preceded the appearance of social monogamy. Plausible causes Opie et al suggest of why male infanticide is the cause of monogamy are the state of social group and ecological condition the specie is in. Monogamy is suggested to have been evolved from polygyny in a high infanticide environment. To reduce infanticide, social monogamous relationships were formed as a result of paternal care shortening the lactation period, presumably because the mother can increase food sources thereby reducing infant care. Paternal care is correlated with the shortening of interbirth intervals and increased reproduction rates. Opie et al also suggest social monogamy was used as an effective counter strategy due to biparental care, increasing the survivability rate of the infant. However, even with both strong pressures to avert into monogamous relationships, studies of the hanuman langurs and gorillas with high infanticide rates have also shown that the pressure to maintain cohesive social groups may render social monogamy as impossible.

In The Evolution of Social Monogamy in Mammals, primates’  cause of social monogamy are believed to be due to breeding females being intolerant of one another. This becomes a mating strategy where males must pick a female to defend due to his inability to multiple. Using a Bayesian approach as comparative analysis of primates in their social system, D Lucas et al has concluded that social monogamy arose from an ancestral past in unstable living groups. Phylogenetic reconstructions have led D Lucas to believe that solitary living has been the condition for all female mammalian ancestors. This evolution where females are solitary creates a problem for males who are unable to defend access from other males to more than one female at a time. This is due to the overlap of home ranges in solitary females. Studies show that in monogamous primates’ home ranges overlap on average by 21%, where as solitary females overlap on average by 49%. This instance paired with social monogamy may also suggest a reliance of high nutritional quality food. Data has also been collected that social monogamous primates consume higher nutritional value foods, whereas solitary primate species consume lower nutritional value foods.

The Evolution of Social Monogamy in Mammals created a more convince argument of which hypothesis of why monogamy appeared. Both articles used comparative analysis in social systems and phylogenetic reconstruction to produce data. But D Lucas et al had used the data amassed to support their hypothesis in an ancestral aspect. The article was structured in a way that addressed on the issues and theories of reason that it could appear by addressing them and their benefits. However, data through overlapping phylogeny suggests otherwise in terms of which factor preceded what as a method of elimination. And though Male infanticide leads to social monogamy in primates is also an excellent article that addresses another compelling explanation on the appearance of social monogamy in primates, it focuses more on the social evolutionary device that may have been use potentially in early humanoids. Opie et al zoom in on the infant’s survivability rather than the parent’s survivability, which Lucas et al do. However, it is a matter of which came first, the chicken or the egg.

Both of these articles are fascinating in the aspect that they use a similar methodology to calculate the likelihood of monogamous mating. Although there have been studies and documentaries that hypothesize monogamy in humanoids, it is interesting to learn about primates’ mating preferences since they do not exhibit the same social tendencies as humans today. The articles have, in fact, changed my understand of monogamy in primates due to the intensity in evolutionary biology data collection and methodology used to amass data. It was most interesting to read about the types of research methodology used to find etiology explanations of evolutionary hypothesis. As a student of the science, procedures and data collection to prove and find scientific information is fascinating to observe. But in terms of the article, both authors made compelling arguments that support both hypothesis and were presented in two different ways. If not both read at once, my beliefs of primates’ monogamous relationships would have been swayed to either article.

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