The current scientific belief for the cause of socially monogamous relationships in mammals is that in predictable environments with high competition for resources, fewer and better-provisioned offspring have a better chance to survive and fulfill their biological destiny: reproduction and perpetuation of their genes. Organisms that fit these characteristics exhibit iteroparity and are classified as k-strategists. K-strategists require a larger amount of energy and maintenance to survive, which is why one parent (in most cases the mother) will care for her young until they can fend for themselves. However, in some cases, the young require a rather large amount of energy and maintenance that one mother cannot provide. The mother would lose her life trying to provide the care needed for her young since she would not be able to allocate energy for herself, followed by the death of her young since they would not be able to fend for themselves. In these cases, it is in the male parent’s best interest to help the mother care for her young, because even though an increased amount of gametes causes males to invest more in the number of offspring that have their genes, if none of those offspring survive, then they are not fulfilling their biological destiny. So, by helping care for their offspring, both parents help perpetuate their genes and form socially monogamous relationships.
The two articles, “Male Infanticide Leads to Social Monogamy in Primates” by Christopher Opie Quentin D. Atkinson, Robin I. M. Dunbar, and Susanne Shultz and “The Evolution of Social Monogamy in Mammals” by D. Lukas and T.H. Clutton-Brock come to different conclusions on the cause of social monogamy in mammals. Opie (et al.) believe that social monogamy in primates developed because longer lactation periods were leading to an increased risk of infanticide committed by competing males trying to reproduce, which led to male parents looking over their young along with the female parents. (Pg. 2, paragraph 4: “This finding hints at one mechanism by which social monogamy may reduce infanticide risk: social monogamy facilitates a shorter lactation period compared with gestation, thereby reducing infanticide risk”). Lukas (et al.) believe that social monogamy in primates developed because low population density in females of species and difficulty in maintenance of male ranges (Pg. 4, paragraph 5: “Our results suggest that social monogamy evolved in mammals where feeding competition between females was intense… and population density was low. Under these conditions, guarding individual females may represent the most efficient breeding strategy for males”).
“The Evolution of Social Monogamy in Mammals” By D. Lukas and T.H. Clutton-Brock makes the more convincing argument for the causes of social monogamy in mammals because while supporting their results with a sufficient amount of data, Lukas and Clutton-Brock also give support for why this the most reasonable explanation. Lukaz and Clutton-Brock state early in their article that phylogenetic reconstruction showed that in the common ancestor of all mammalian species, the females were solitary and males occupied ranges of territory. They then go on to state that the likelihood that common ancestor was solitary was 0.99 for all approaches, one of the many examples where statements were backed by data results. In a flow that is easy to follow, Lukas and Clutton-Brock follow this early statement with later results that show social monogamy becoming much more common once female population density started to decrease. Along with this, Lukas and Clutton-Brock give reasons for why male care and male infanticide are not valid explanations for social monogamy in mammals.
These articles have most definitely changed my personal understanding of social monogamy in mammals through the developmental details and evolutionary history of social monogamy. Before, I never thought about the kinds of environmental changes or situations that could lead to the birth of socially monogamous relationships in primates. For example, a change in diet could lead to less dense female populations in mammals, which would in turn lead to males having trouble maintaining their ranges of control. This would eventually be a cause for social monogamy in that species. The most surprising thing I read came from Christopher Opie’s (et al.) article, which brought up a point about how encephalization could lead to social monogamy. I found it very interesting how encephalization leads to longer periods of lactation, increasing the risk of male infanticide. This increased risk of male infanticide led to males sticking with female parents to protect their offspring and fulfill their biological destination through these means. Personally, I thought that both articles offered very compelling and legitimate arguments, and that it could be a combination of both leading factors mentioned in the articles that led to the birth of socially monogamous relationships in primates and other mammals.