Social Monogamy in Mammals

Previous to reading this article, we believed that the main reason that social monogamy arose was because of the necessity of paternal care. In a majority of species in which social monogamy was observed, the offspring had long developmental periods. This meant that it was very difficult for the mother to safely take care of both the offspring and herself, making paternal care necessary for the survival of their offspring. However both of these articles claim that paternal care is a byproduct of social monogamy and each cite a different reason as the cause.The article “Male infanticide leads to social monogamy in primates” by Opie, Atkinson, Dunbar, and Shultz claims that male infanticide is the true cause. To dispel the belief that paternal care lead to social monogamy, they looked at the phylogeny of socially monogamous species. They found that paternal care actually came after the development of socially monogamy and therefore could not be a cause. They then analyzed that since male infanticide occurs in species where the duration of lactation is longer then the duration of gestation and social monogamy lowers the lactation period, it makes sense that males would become monogamous. In this cause monogamy both pretects their offspring, and means that the female is able to reproduce with the male more frequently.

On the other hand, the article “The evolution of Social Monogamy in Mammals” by Lukas and Clutton-Brock claims that social monogamy is the result of a males inability to defend access to multiple females. To come to this conclusion they started by analyzing the three majors theories: Paternal care, preventing male infanticide, and low access to multiple females. Using phylogeny to look at the evolution history of social monogamy they found that paternal care developed after social monogamy instead of causing it. Upon looking at male infanticide they disproved one of the assumptions of the other article by pointing out that in only 27% of socially monogamous species the duration of lactation exceeds the duration of gestation. This make male infanticide incredibly uncommon, therefore weakening the validity of this theory. However when they analyzed the theory based on low defensibility of females they found good evidence in the phylogeny of social monogamy. They observed that nearly all species that exhibited social monogamy, females were solitary and that these species lived in much lower densities then solitary species. I found the paper by Lukas and Brock to be much more convincing because of its direct counter argument to the other. Perhaps this is simply the advantage of publishing second but I found that it pointed out a major flaw of the first article. The idea that the prevention of male infanticide lead to social monogamy, was largely based on the idea that socially monogamy arose in species where male infanticide was a threat and the article greatly detailed why male infanticide occurred. It explained that male infanticide was an issue where males benefited from killing offspring so that lactation would end and the female would be available to mate. This argument become incredibly weak when Lukas and Brock pointed out that only 27% of species met that condition. Admittedly not all of the species met Lukas’s and Brock’s condition that females were solitary, but 44% compared to 27% is much more convincing.

Personally, I was really surprised by these articles. I wouldn’t have expected paternal care to be a result of social monogamy. It always made sense to me that it was the reason, since primates often have much longer periods of development as a result of larger brains. I also had never understood why male infanticide was a trend or issue in species since I never thought why the child would prevent mating. I learned a lot about not only social monogamy in primates but about the motivations of animals for both mating and care of their offspring.

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