Monogamous relationships in mammals, while rare, still happen due to the needs of the offspring. If the offspring have little to no needs then there is no parental involvement. However, if the offspring require more food than one parent can supply, a male may increase his reproductive fitness by being in a monogamous pair and helping to care for the offspring rather than going off in search of more mates to reproduce with. Additionally, the monogamy pairing guarantees the male that the offspring is his so he would be more willing to invest in paternal care.
Male infanticide leads to social monogamy in primates by Christopher Opie, Quentin D. Atkinson, Robin Dunbar,and Susanne Shultz states that the main reason for social monogamy in mammals is male infanticide. Primates have large brains, which is “associated with long development and lactation periods” (Opie et al.). This makes primate infants vulnerable to infanticidal males (Opie et al.). Fathers can also provide protection against other males from killing their offspring, since a male who is not the father can kill an infant so that the female can return to reproducing faster. With both parents caring for their young, the lactation period can be shortened which reduces the risk of infanticide and increases reproductive rates. According to Opie et al., “high male infanticide alone consistently preceded the appearance of social monogamy across primates”. The article does state that a switch to social monogamy may only be possible when ecological conditions are met.
The Evolution of Social Monogamy in Mammals by D. Lucas and T. H. Clutton Brock states that the reason behind monogamy in mammals is due to females who are intolerant of each other and low female density, which “represents a mating strategy that has developed where males are unable to defend access to multiple females.” Monogamy is a way for males to guard their females from other males from territories that overlapped multiple territory ranges of females. Social monogamy also seemed to have been evolved from one ancestor where females were solitary and lived in individual territories with males roaming independently (Lucas and Brock, 2013). There was competition between females which lead to intolerance of one another and low female densities due to a change in diet. Due to low female density, it prevented males from guarding more than one female so guarding only one female was the most efficient strategy for males (Lucas and Brock, 2013). According to the article, paternal care has been appeared prior to social monogamy, so “it is unlikely to be a precondition for its evolution (Lucas and Brock, 2013).
I think the article about infanticide leading to social monogamy had a more convincing scientific argument because they looked at other things such as primate phylogeny and primate trait data and used that to analyze as opposed to just strictly looking at data like the other article. Opie and others were very specific in determining the definition in paternal care and used data on infanticide from wild populations. They also looked at cases of infanticide from direct observation and accounted for biased observations of infanticide. I liked that they used a framework to model the evolution of traits along the primate phylogeny which brought their work on the phylogeny and data together, whereas the other article strictly used statistics in supporting their evidence. Opie and others also included their methods at the end of their article which made it easier to follow and to see how they did it, as opposed to a bunch of numbers and a median which was hard to understand.
These articles have changed my understanding of primates because both articles included information that I had never learned about before. I had learned about primates more in anthropology class than in biology (it was a whole unit), but I was still surprised and sad that male primates would kill infants just to have the female be ready to reproduce again. The article by Lucas and Brock was also surprising because we had learned that monogamy ensures that the offspring is the male’s, so if needed he would help care for the young and the article states evidence that goes against it. I liked how that instead of males competing against each other for resources, it was females this time, competing against each other and even becoming intolerant of each other so males couldn’t do anything about it except stick to one female and become a monogamous pair.