Social Monogamy Blog

1. We currently believe the reason for monogamous relationships in mammals is due to a few factors. Some offspring require more food and care than a single parent can supply. This might cause the male parent to care for the offspring rather than searching for more mates because it increases his reproductive fitness by ensuring a viable offspring. Also, a reason monogamous relationships occur in mammals is due to the fact that in a monogamous relationship, the male can ensure that they are the father of the offspring, therefore ensuring that they passed their genes successfully and increasing their reproductive fitness.

2. “The Evolution of Social Monogamy in Mammals” by D. Lukas and T. H. Clutton-Brock, determined the root cause of social monogamy in primates is solitary females. Due to females occupying small discrete areas away from other females, males have difficulty seeking out more than one mate.  They found that social monogamy evolved in mammals “where feeding competition between females was intesnse, breeding females were intolerant of each other, and population density was low” because these conditions made male guarding of individual females advantageous. In almost all of their tests, the data showed social monogamy was derived from an ancestor with solitary females.

“Male infanticide leads to social monogamy in primates” by Christopher Opie, Quentin D. Atkinson, Robin I. M. Dunbar, and Susanne Shultz determined that male infanticide was the root cause of social monogamy within primates. The article stated “Where lactation is longer than gestation, females are expected to avoid suckling two infants of different ages simultaneously by delaying the return to oestrus after parturition. Where oestrus is delayed, it can pay a male who is not the father, to kill an unweaned infant so that the females returns to oestrus sooner.”  Therefore, a male guarding its young in a monogamous relationship is advantageous to the male’s reproductive success. Furthermore, the study stated that monogamy creates a shorter lactation period because the female does not have to work as hard to raise the offspring, thereby reducing infanticide.

3. I believe “The Evolution of Social Monogamy in Mammals” was a more convincing argument. This article was more convincing due to its methodology, counter arguments, and extensive data analysis compared to “Male infanticide leads to social monogamy in primates”. This articles methodology was more compelling due to its much larger data set. While “Male infanticide leads to social monogamy in primates” used 230 primate species, “The Evolution of Social Monogamy in Mammals” used data from 2545 mammals. Furthermore, “The Evolution of Social Monogamy in Mammals” was a more convincing argument due to its extensive data analysis, where the article had much more data within the text and within its graphs compared to “Male infanticide leads to social monogamy in primates”. This data included likelihoods for common evolutionary ancestory using “all approaches to reconstruction evolutionary sequences” to support their argument. Also, “The Evolution of Social Monogamy in Mammals” had much better counter arguments. This included that there was “no evidence of any form of male contribution to care in 94 of 229 (41%) socially monogamous species” which counters “Male infanticide leads to social monogamy in primates” argument because it stated that male contribution to care was the reason there were socially monogamy in primates. While it does not counter that male contribution does cause social monogamy in primates, it proves that the data for that argument is much too narrow and specific. Additionally, “The Evolution of Social Monogamy in Mammals” states that “male infanticide is typically found in species where the duration of lactation exceeds the duration of gestation: This is the case in few socially monogamous species (20 of 75 species, 27%) compared with species where females are solitary (44%).” This further proves that the data set in “Male infanticide leads to social monogamy in primates” is much too small, and does not provide evidence of the origins of monogamy outside of primates.

4. These articles have changed my understanding of monogamy in primates. While I already knew that limited resources and competition were factors to monogamy, I did not realize that infanticide and solitary females were also major factors in the origins of monogamy. There were a few surprising facts in the article; the two most surprising facts to me were that infanticide may be why humans are monogamous and that monogamy is stable, meaning that once you transition to monogamy you cannot transition back.

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