Lukas and Clutton-Brock begin their discussion by dismissing the generally held idea that social monogamy is derived from group living that is unstable. Although if both sexes did live together and were unstable, this could lend support to the idea that male infanticide led to group living. However, Lukas and Clutton-Brock dismiss this hypothesis in favor of the hypothesis that the evolution of social monogamy was seen as a result of female solitary living and male ranges overlapping those ranges. According to Lukas and Clutton-Brock social monogamy arose in groups of mammals where “feeding competition between females was intense, breeding femalses were intolerant of each other, and population density was low.” The fact that competition between females was intense and females were intolerant of each other drove females to solitary living and not group living. It also drove them far away leading to a low population density because the competition for foods was so intense. That low population density made it difficult for males to monopolize access to more than one female because of the distances between their ranging patters. This led to males choosing to form a monogamous pair with one female and monopolizing her reproduction. According to the Opie et Al. however, the rise of social monogamous relationships is due to a combination of the two factors of female ranging patterns and male infanticide. In the article published by Opie, Atkinson, Dunbar, and Schultz, their tests yielded that “high male infanticide alone consistently preceded the appearance of social monogamy across primates.” Social monogamy was a “counter-strategy” boon of sometimes leading to biparental care so that the male could offer protection of his offspring from other infanticidal males. It also leads to “hastening oestrus resumption” in the female. Because the delayed returning to oestrus was the reason for many males to commit infanticide so through social monogamy, the chance of mammals surviving and passing down their traits is more probable because there is more protection from male infanticide. Both articles discuss the evolution of biparental care not as a cause of evolution, but as a correlated product of the social monogamy. Tests indicated “paternal care is a secondary adaption” according to Lukas and Clutton-Brock.
Both articles used studies of comprehensive statistical analyses to check their hypotheses of causality. However, I believe that Lukas and Clutton Brocks studies hold more accuracy namely because of the huge sample size. The larger the sample size in statistics, the closer the sample mean and proportions approach the population mean and proportions. The two scientists used 2545 species in their analyses or all the mammalian species that could be classified. While Opie et al. had many of the same research methodology as Lukas and Clutton-Brock using Bayesian inference, their study only took into account 230 of the primate species. In addition, Lukas and Clutton-Brock’s work with population density not only uses a large sample size of 230 but it also shows definitively the difference in mean population densities between socially monogamous and solitary species with a probability less than 0.001 that their mean population densities are the same. Lukas and Clutton-Brock also used many more different forms of statistical analysis than just Bayesian inference using the ANOVA test to measure variance and Wilcoxon to measure to find the prevalence of male infanticide in species where lactation occurs for longer than gestation.
The most surprising thing to me in these articles was a piece of information that the authors largely took for granted. I had no idea that males would kill weaning infants of females they were trying to mate with to speed up their return to oestrus. The concept of infanticide is extremely vindicated in human society that I could not understand it in a social context. Also, in our unit of population ecology we learned about inclusive fitness and kin selection which made me wrongly believe that generally animals tend to look out for each other. The simple biological truth though is that that unweaned infant will not perpetuate the genes of the male that is attempting to mate because it is not kin, so to fulfill its biological density of Darwin, it has to remove the obstacles that are keeping it from reproducing and perpetuating its genes. Humans have developed this idea past kin selection where all babies are seen not as a perpetuation of specifically someone’s genes, but a perpetuation of the species as a whole. We also reference children and infants as “the future” of human existence which really highlights how we have evolved past primates with respect to kin selection I feel. Still, though, even though I understand the biological motive of infanticide, it is impossible for me having grown up in the society that I have grown up in to wrap my head around the idea, especially because culturally primates are associated with humans so much in common culture and phylogeny.