Social Monogamy

Mammals in monogamous relationships have two reasons for doing so. The first is to have the increased ability to provide food and protection to their offspring from contributions from two adults, therefore increasing the likelihood of survival of their offspring, especially since mammals take longer to sexually mature. The second is to have certainty of paternity, ensuring the propagation of the male’s genes.

In “The Evolution of Social Monogamy” D. Lukas and T. H. Clutton-Brock argue that monogamous relationships in mammals evolved as a mating strategy because males are “unable to defend access to multiple females.” This inability may have been caused either by “mutual intolerance between breeding females (Emlen, Oring)” or because “large female home ranges prevent effective defense by males of territories covering the ranges of more than one female (Wittenberger, Reichard).” Lukas and Clutton-Brock argue that monogamous relationships developed out of “solitary behavior of female ancestors, whose high body masses called for increased competition” amongst one another for food. Because of this high competition, as well as large territories among females, the most efficient breeding strategy for males was to simply breed with one female, causing the rise of social monogamy in mammals.

In “Male Infanticide Leads to Social Monogamy in Primates, Opie et al argue that the origin of social monogamy was caused by long lactation periods of females, making primate infants particularly vulnerable to infanticidal males. Social monogamy “facilitates a shorter lactation period compared with gestation, thereby reducing infanticide risk (Opie et al).” Social monogamy also provided a counter-strategy to male infanticide because one or both pair-members could defend the infant. Because apes also have larger brains, social monogamy helps to overcome problems posed by high developmental and metabolic costs of large brains by allowing for slow reproductive rate without increased infanticide risk.

The data analysis of “The Evolution of Social Monogamy” is superior to that of “Male Infanticide Leads to Social Monogamy in Primates” for a few reasons. In the former, Lukas and Clutton-Brock defined their variable definitions, for example, defining the properties of “solitary”, “socially monogamous”, and “group living” primates so that future scientists could repeat their experiment as needed knowing the operative definition of these three groups. Lukas and Clutton-Brock also found the p-value for all of their experiments, narrowing the rate of error to 5% or less, a very low likelihood of having incorrect data. They also took most of the beginning of their report to specifically refute each possible hypothesis with specific mathematical data, instead of more general information as Opie et al did in the latter article. Lukas and Clutton-Brock also have more sources (44 as opposed to 31), and use them well, allowing them to further develop their thesis with data that supports it.

Before reading these articles, I only saw monogamous relationships through the eyes of the human race. I knew that it was advantageous, allowing us to give more care to our offspring, who demanded more care during a longer period of growth and development. However, the human version of social monogamy is at present subject to other societal factors, like the rising rate of divorce. The articles gave me a glimpse into the history and evolution behind primates’ start as solitary beings to their present state of being monogamous beings. This gave me a background as to why this behavior exists in nature. However, I was surprised by the fact that gorillas have a high rate of infanticidal males because they live in areas with high predation rates. I always assumed they, like other primates, lived in monogamous relationships. However, their reason for not doing so is simple and the most advantageous: group living allows them more protection against predators and is a better adaption toward keeping offspring safe in the dangerous habitat they live in than monogamous relationships would.

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