Research Articles

An organism’s main goal in life is to reproduce and pass on his or her genes. However, for this to happen their offspring also need to survive. Monogamous relationships in mammals occurred to ensure that the offspring would survive and the genes of the parents would be passed on. A male has a better chance of leaving more viable offspring in a monogamous relationship rather than a polygamous one. With the protection and care of both parents, the offspring is less likely to be preyed upon or die from lack of resources such as food and shelter. Monogamous relationships also ensure the male that his genes are being passed on because while the female knows the offspring is hers, the male has no way to be sure the offspring is his. In a monogamous relationship, the male could guard the female and ensure that the offspring is his and therefore passing on his genes.

In the article “The Evolution of Social Monogamy in Mammals,” D. Lukas and T.H Clutton – Brock determine that the cause of social monogamy in primates is when “breeding females are intolerant of each other and female density is low.” A socially monogamous relationship allows a male to be able to guard individual females when they are in competition for resources and otherwise intolerant of each other, an “efficient breeding strategy for males.” Lukas and Clutton – Brock claim that “it has evolved where females are solitary and males are unable to defend access to more than one female at a time” suggesting that males had a harder time passing on their genes by inseminating multiple females because they were so spread out. By mating with only one female they would ensure that their offspring would pass on their genes. According to their research, “the high incidence of social monogamy in Primates and Carnivora compared with herbivorous orders…maybe a consequence of a reliance on resources of high nutritional quality but low abundance” implying that females are competing against one another for a limited amount of resources to ensure their offspring’s survival causing them to be intolerant of each other. In a socially monogamous relationship, however, both parents would be able to forage for food increasing the offspring’s chance of survival.

In the “Male Infanticide Leads to Social Monogamy in Primates” article, Christopher Opie, Quentin D. Atkinson, etc. determine that the cause of social monogamy in primates is due to male infanticide. Their data suggests that “biparental care shortens relative lactation length, thereby reducing infanticide risk and increasing reproductive rates” which allows a male to leave more offspring and is therefore more advantageous. In a monogamous relationship, the risk of male infanticide would decrease because of “parental care in the form of male protection and provisioning” which would cause both males and females to stay in that relationship. Opie states that “male infanticide precedes the switch to social monogamy” while the other factors such as biparental care came after. This means that because there was such a high rate of male infanticide, socially monogamous relationships evolved to prevent that.

While both articles were convincing in their own way, I found “Male Infanticide Leads to Social Monogamy in Primates” article more convincing. Their methodology was much clearer than the other article and it was easier to follow and understand their process. For example, to explain how the researchers analyzed the primate phylogeny, they “inferred maximum – clade credibility tree from the complete 10kTrees sample using TreeAnnotator…six known fossil calibration points” which explained how they were able to obtain the data. In addition, their argument was logical in claiming that male infanticide would lead to monogamous relationships because every species wants to ensure the survival of themselves and their offspring. A monogamous relationship would allow them to guard the female against other males and protect their offspring. Opie and the other researchers also found that biparental care and other factors evolved after monogamous relationships which suggests that they did not play a significant role in the evolution of monogamous relationships in primates. The only factor that preceded the evolution of monogamous relationships was male infanticide.

These articles did change my understanding of monogamy in primates because I never considered the reasons for a monogamous relationships. In the evolution in my anthropology class, we learned that primates tended to live in groups for protection and because they were/are social animals. It makes sense to me the reasons for the evolution of monogamous relationships from both articles and both were new perspectives for me. I never really considered primates other than humans as monogamous because of their living situations. I think the most surprising aspect that I just read was male infanticide. Maybe I was just thinking emotionally but I was horrified to learn that males would kill infants to reduce that lactation period so the female would return to the estrus cycle faster.

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