Though generally rare in most species, socially monogamous behavior, where mates live in pairs, has evolved in mammals. This can be a result of many factors, though it is uncertain which the root cause is. In mammals where social monogamy is common, offspring are often unable to obtain the necessary resources for their development from a single parent. Thus, the male can increase his reproductive fitness by supplying the necessary care for offspring, rather than searching for other mates during the long gestation and nursing periods. There is also the idea that, in a population with relatively less females, males choose to remain with a certain female in order to definitely secure a mate.
In “The Evolution of Social Monogamy in Mammals,” Lukas and Clutton-Brock begin their article by immediately refuting the ideas that male infanticide (as cited in the other article as a cause) and paternal care (which, they explain, is instead a consequence) are root causes for social monogamy. They assert that, in areas where female density is low, males are unable to mate with multiple partners, and thus invest more effort and resources in securing one single mate. The transition to social monogamy, they suggest, is due to ancestral species with solitary females whose territories do not overlap, and roaming males who overlap with several others. The females require their own resources, and do not tolerate other breeding females. Thus, a male is often forced to select one breeding female to guard.
In the article written by Opie, Atkinson, Dunbar, and Schultz, as the title suggests, social monogamy stems from male infanticide. When a female is raising multiple offspring, it can take a female longer before she is again a viable mate. Thus, another competitive male, who is not the father of said offspring, may sometimes kill the youngest infants in order to increase his own viability, as the female would become a potential mate sooner. A “resident male,” in a monogamous relationship, would be able to defend his own offspring from infanticide, and thus becomes more viable.
I thought that Opie et al presented a more convincing argument. Their theory simply made the most sense for social monogamy evolving to increase an organism’s viability. Furthermore, it seemed to align with the theory that biparental care is necessary in providing resources and protection. I also didn’t agree with Lukas and Clutton-Brock, who presented the theory of mate-guarding as mutually exclusive to the infanticide theory. This theory also seemed questionable, as I was not completely convinced that solitary females would totally discount the potential for males mating outside of one range. They also did not do much to refute the other theories that they discounted.
My ideas prior to the reading were mainly built around the ideas of parental care and providing resources. While the theory that was most convincing to me was still viable within these other ideas, I was really shocked by the relatively common practice of male infanticide, and thought that was a very interesting potential cause of the evolution of social monogamy.