Monogamy

Based on previous in class lecture and textbook readings, I believed that monogamous relationships stem from a need for extensive parental care, typically by species whose offspring need a large and constant supply of food, such as most birds. I learned that for monogamous species, males are most likely to leave viable offspring by helping one female to care for dependant offspring than seeking multiple mates.

From a purely Darwinian perspective, monogamy- that is having only one mate during one’s lifetime or at a time- seems counter intuitive and not at all advantageous for a male to carry on his genes. Therefore, the topic has sparked the interest of many scientists and researchers who are interested in discovering how monogamous mating evolved and why it is advantageous.

Two independent research teams studied monogamy and came up with two different results.  Opie’s team of 4 scientists (Opie, Atkinson, Dunbar and Schultz) found that in primates, male infanticide.  Because the lactation periods in primates are long, infants are especially vulnerable to male infanticide which is the intentional killing of infants by other males in a population to decrease competition. According to Opie’s team, in order to protect their offspring, primate males have evolved to practice monogamous mating.  Opie’s team cites that “…as well as strong correlated evolution between male infanticide and mating systems, male infanticide precedes the switch to social monogamy” whereas parental care evolves after the switch to monogamy and female ranges arose independently. Such is their argument against the other two perspectives on the matter.

On the other hand, Lukas and Clutton Brock published an article that argues that female ranges, specifically the low density of females in an area causing males to have limited access to multiple mates, is the main cause for monogamy in mammals such as primates. Lukas and Clutton Brock give two reasons for this: either females were intolerant to each other or females needed larger home ranges. Lukas and Clutton Brock actually cite Opie’s team saying “A recent comparative analysis of primate social systems.. concluded that social monogamy …may be associated with the risk of male infanticide.” Lukas and Clutton Brock argue that this is unlikely because in other taxonomic groups besides mammals, breeding females occur much less.

I thought that the team of four scientists, Opie, Atkinson, Dunbar and Schultz made a more convincing argument. The way that they formatted the article was easy to understand and follow logically. First, they simply stated their argument, then followed it up with the three leading hypothesis for monogamy, then continued to rationally disprove each theory. Finally, using phylogenetic comparative methods, they made a strong, quantitative case for their position that monogamous mating is most caused by infanticide. Although both articles agreed that parental care could not be the source of monogamy, I did not think that Lukas and Clutton Brock had enough concrete evidence against infanticide as the primary source. Furthermore, Opie’s team cites the counter argument more times than Clutton Brock and Lukas, which leads me to believe that they address specific details more concretely.

Both articles changed my view on monogamy because prior to reading these, I was convinced that the leading evolutionary cause was the need for extra parental care in order to increase survivability. However, both articles surprised me by showing how this could not be the case. “It (biparental care) is not ubiquitous in socially monogamous mammals. It may be that rather than high cost offspring giving rise to monogamy, monogamy enables the production of high cost offspring”, Opie, Atkinson, Dunbar and Schultz write. “ Lukas and Clutton Brock agree, “Male care is probably a consequence rather than a cause of the evolution of social monogamy”. This was especially surprising to me.

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