Monogamous relationships exist in mammals to increase the likelihood of the survival of offspring. All organisms must find a balance of investment of energy between the quantity of their offspring and the quality of care they receive. Mammals, being K-strategists, invest more time and effort into individual offspring, giving individuals a better survival rate. Monogamy is an extension of this: the father has higher insurance that the offspring are his, so he is more willing to invest energy in protecting and feeding them.
According to Opie, Atkinson, Dunbar, and Shultz, “the most compelling explanation for the appearance of monogamy is male infanticide”(abstract). Lukas and Clutton-Brock propose instead that “social monogamy evolved in mammals where feeding competition between females was intense, breeding females were intolerant of each other, and population density was low”(discussion). The latter presume that social monogamy evolved because of conditions that allowed males to defend access to only female.
I found that the Lukas article made a more compelling argument, mainly because it invalidated the other argument and criticized their methods. I realize that this was impossible for the Opie article to do, since it came first, but knowing that Lukas could view the results of both experiments adds furthur to his credibility. Lukas et al. reduce the connection between monogamy and male infanticide to “an independent evolution of the two traits.” Later, they write that “Shultz et al. classify socially monogamous species that are accompanied by nonbreeding offspring as group living and do not distinguish between social systems of this kind and plural breeders, where groups include several breeding females.” Because Lukas et al. examined the choices of the Opie study in addition to creating their own, one hopes that the second study was an improvement upon the first.
My understanding of monogamy in primates has not truly shifted, because what they observably do is non-negotiable across various sources. What they debate instead is the history of how primates have come to behave as they do. I now more thoroughly understand the various advantages of monogamy in primates, and it was interesting to learn why certain circumstances, such as low population density, might have led to monogamy. However, the most surprising revelation for me was that the smallest alteration of a bound of categorization, such as what is classified as group living above, can have a great impact on the results of a study. What is really strange about it is that some decisions researchers make along these lines may be arbitrary at the time but later skew the data.