Monogamous relationships typically arise in situations where both parents must care attentively to their offspring. The needs of the child requires high energy investment and thus has the potential to cause tighter relationships among parents. This can only work in species that exhibit K selection and iteroparity. There is also a certain degree of territoriality associated with monogamous living situations. In birds, most of which are monogamous, nesting behavior is exhibited. Similarly, in primates, in which about 25% of species are monogamous, there is a high degree of territoriality among males. One male’s territory includes both access to resources of land and females. In monogamous relationships, it is advantageous for males because they can ensure a child is indeed theirs.
The male infanticide article introduces the possibilities of monogamy arising from high energy investment in raising offspring, females occupying smaller ranges, and male infanticide. However, they assert that, “high male infanticide alone consistently preceded the appearance of social monogamy across primates.” (Opie et al) Male infanticide is caused first of all because the period of lactation in females is longer than the period for gestation. Males would thus be tempted to kill an infant so the female can return to gestation. Monogamy is a mechanism by which animals can reduce the rates of male infanticide.
The Evolution of Social Monogamy article suggests that monogamous relationships have arisen from multiple causes. They assert that females must exhibit less sexual dimorphism, and must occupy larger ranges of territory. This makes it harder for males to claim females as there, becoming an “effective defense by males of territories covering the ranges of more than one female.” (Lukas et al). Furthermore, they acknowledge among all mammals except primates, monogamous relationships arose in solitary relationships. Solitary living renders males “unable to defend access to more than one female at a time.” (Lukas et al). Also, solitary ancestors to socially monogamous mammals means that breeding females are intolerant of each other, further contributing to the benefit of monogamy.
I believe the Lukas et al article has a better argument for monogamy because the Opie et al article looks solely at monogamy among primates. Lukas acknowledges that monogamy has evolved in other clades to include species such as the dik-dik, night monkeys, small clawed otters, and the elephant shrew. Though male infanticide may be the most prevalent preceding practice to social monogamy across primates, this may not be the case for all mammals. The Lukas article also shows positive correlation between socially monogamous species and solitary species (low population densities have high instances of monogamous relationships) on a graph, which adds to their validity. The Lukas article also acknowledges male infanticide, however believes it is not an important factor in monogamy because it only occurs in about 27% of socially monogamous species.
I was surprised to learn that monogamy in primates arose as a defense mechanism against the killing of competitors’ children. The article has also taught me that once species transition into social monogamy, infanticide usually does not occur. This makes sense because of what we learned in class, that males in monogamous relationships have assurance that children are theirs, and therefore don’t need to kill other children to get to a female who is also theirs. Reading these articles also broadens my view because I did know that one defense against infanticide was completely the opposite of monogamy, as displayed by the extremely polygamous bonobo species.