The Causes of Social Monogamy in Primates

Though monogamous relationships in mammals reduce reproductive opportunity by limiting each organism to one mate, they increase the viability of the offspring, and therefore perpetuation of the parents’ genes, in a variety of ways. Many mammals exhibit iteroparity, which favors the survival of the offspring over opportunities to reproduce. As offspring size and time until sexual maturity increase, they usually require more parental care. When this exceeds the care that the mother has to offer, other help is needed. Monogamous relationships are one solution to that problem. In polygamous relationships, only the female can guarantee that the offspring she carries is her own whereas the male cannot. In a monogamous relationship, the male can better ensure that the offspring his mate carries is his. These articles have not so much changed my understanding of monogamy in primates as they have deepened it. From our class discussions, I had already concluded that monogamy in primates must provide some advantage to the offspring as well as the parents in order for it to be perpetuated. We had discussed some of the benefits of monogamy, such as increased viability of the offspring under the care and protection of two parents, both of whom know that the offspring is their own, and time allowed for passing down developed behaviors crucial to the offspring’s survival. What these articles did was add to the list of advantages social monogamy provides, as well as specify why it has not evolved in all primates. I had not been aware of the ways in which the density of females might affect a male’s mating practices or the prevalence of male infanticide in those species. What surprised me in particular was the idea that instead of the increased needs of the offspring necessitating higher paternal care and therefore making a monogamous relationship more advantageous, more often social monogamy developed first and allowed for more paternal care as a result.

Opie et al. conclude that social monogamy in primates is a result of high male infanticide rates. They acknowledge that discrete female ranges and paternal care are also related to social monogamy, but claim that those traits followed the shift to social monogamy rather than caused the shift. They supported this idea by saying that a socially monogamous relationship allows both parents to defend the offspring if necessary, therefore decreasing the incidence of infanticide. Additionally, infanticide can be lowered by shortening lactation time, which is also associated with social monogamy. Lukas and Clutton-Brock claim that intense feeding competition between females, intolerance between breeding females, and low population densities make it advantageous for males to enter socially monogamous relationships. They agree that increased paternal care followed the shift to social monogamy rather than preceded it. They also acknowledge the connection between social monogamy and low male infanticide, but claim that it is “unlikely to be the principal mechanism” (Lukas and Clutton-Brock). Each conclusion is supported by comparing the percentages of where the trait or behavior is present in socially monogamous species and polygamous species.

Lukas and Clutton-Brock article makes a more convincing scientific argument. It seems more logical that a variety of influences would have contributed to the evolution of social monogamy in primates, not solely male infanticide rates. The Lukas and Clutton-Brock article follows each proposed cause of social monogamy with the relevant data enabling a direct connection to be made between the data and their analysis, which further increase the credibility of their argument. Opie et al. supplement their conclusions with only two small data tables and are less transparent with their calculations. Lukas and Clutton-Brock also provide the sample size of each of the groups they are considering and are much more explicit about what they consider a socially monogamous species.

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