One of the reasons we currently believe that monogamous relationships exist in mammals is that the commitment of paternal care exhibited by a male can ensure the survival of its offspring. For example, the male can assist in finding food for his offspring and protecting his offspring from predators. This is an investment a male might make when he knows that he has sired offspring. Lukas and Clutton-Brock state that social monogamy became a practice as a result of higher competition between females and low population density, particularly of females. As stated on the last page of their article, this competition between the females of a population has made it more efficient for males to guard one female than to attempt to sire offspring with more than one female. This is because they would create a lower probability of their offspring surviving if they abandoned the female after mating. On the other hand, Opie et al. state that infanticide is the determining factor in the evolution of social monogamy. Their results support the argument that social monogamy evolved after an increase in male infanticide. Opie et al. also mentioned a popular reason for the presence of male infanticide which is that the infants are very vulnerable during the long lactation periods of female mammals.
I think Lukas and Clutton-Brock made a better scientific argument in their article because they used a larger sample size of 2545 mammalian species (versus the 230 primate species analyzed in the other study). Although the article by Opie et al. was clear and they specified the efforts they made to reduce the effects of sampling issues (page 13330), Lukas and Clutton-Brock provided a much greater amount of data. In my opinion, science is best supported by as much data as possible along with a proposed reason as to why a set of data suggests what it does. I think Lukas and Clutton-Brock were able to do this through the use of frequent citations of data which supported the statements being made about the behavior of primates over generational periods.
The concept I found most surprising when reading these articles was the argument that paternal care is a behavior that was most likely exhibited in primates after they began practicing social monogamy. This was surprising because I thought that social monogamy would arise as a result of increased paternal care, and the increase in paternal care would have been the result of a decrease in resources and survivability of the offspring. These articles have definitely changed my understanding of monogamy in primates because I did not realize that male infanticide could be such an important factor in predicting the survival of offspring. The argument that social monogamy arises when there is a low population density of females also got me thinking about why a decrease in the number of females in a population (and the resulting increase in competition between the females) would occur in the first place. Lastly, I found it interesting how the concepts presented in these articles could be applied to human populations. I hope that more research can be done on this topic in an effort to better understand how human behaviors have evolved.