Monogamy in Mammals

A monogamous relationship in animals is one where both parties mate only with each other and not with other individuals in the general population. This kind of behavior seems counter intuitive, bearing in mind that fitness in animals is measured by how well they can pass on their genes to future generations. It would therefore make sense for a male individual to want to reproduce with as many females as possible to proliferate his genes. In mammals, only a small fraction of species actually participates in monogamous relationships. Mainly, this has to do with the male’s certainty of parenthood as well as the viability of youth. When a male remains with a female after mating, he ensures that she will not mate with other males and possibly produce offspring with their genes. Once the offspring is born, and with the male having known it is likely his, a monogamous relationship can increase the viability of the offspring. Since many species of mammals exhibit K-Selection in which less offspring are produced and are given greater care, it would make sense that the male would put greater care into ensuring his offspring are protected. His presence can protect the female which can be breast feeding the offspring as well as the offspring itself. In the case of mammals that exhibit K-Selection, this monogamous set-up makes more sense than a polygamous set-up where the male would have little certainty of parenthood and have a lesser impact on protecting his offspring directly. The article by D. Lukas and T.H. Clutton-Brock suggests that the primary reason for monogamy in animals is an evolutionary consequence. It argues that monogamy developed in mammalian species where the females were once solitary and males were unable to protect more than one female at a time, so they had to stay with just one. This is supported by the fact that monogamous species have a lower population density (15 individuals/km squared) than solitary species (156 individuals/km squared). The article also says that males caring for their young is not a cause of monogamy because it is only seen in 59% of monogamous species and cites the absence of an explanation of why male infanticide rates are lower among monogamous species. The writers make the determination that these are merely consequences of the formation of monogamous species. However, the article by Opie et. Al suggests that male infanticide is the reason why monogamy developed. This is backed by the observation that the other two likely causes, monogamy for paternal care or to guard mates, only comes after the adoption of monogamy unlike switching for the sake of lowering male infanticide rates which indeed precedes it. The explanation is that the shift to monogamy was high in places where polygynous species had high infanticide rates and that it can actually ease these rates. The paternal care which comes as a consequence of monogamy decreases lactation time, which when compared to gestation time is low, leads to lower rates of male infanticide. Though both sides present valid arguments, Lukas and Clutton-Brock provide a more convincing argument. They provide a very great deal of data to back up their claims that monogamy arose as a consequence of males being unable to defend multiple females as compared to Opie et. al who provided sound argumentation, but lacked in statistical analysis. Indirectly, the article by Opie et. al even admitted that Lukas and Clutton-Brock were correct, saying “the Switch to monogamy may only be possible where ecological conditions permit” (Opie, 13329). This is consistent with the hypothesis that monogamy occurred as a response to males being unable to defend multiple females. Lukas and Clutton-Brock back up this claim with statistical evidence: that population densities are lower in the species practicing monogamous relationships than solitary ones. The articles have changed my understanding about monogamy in primates because they have given me a variety of reasons explaining why it occurs. Previously, I would have simply assumed that it had to do with ensuring offspring vitality, when in reality, both articles claim that is not the case. I did not realize that preventing male infanticide as well as a response to males being unable to defend multiple females for territorial reasons contributes to monogamy in mammals. The most surprising thing I read, however, was that monogamy is very uncommon – only about 3% – in mammals. I always assumed that it would be much higher and be more representational of the human monogamous model.

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