OK, I waited way too long to get to this post. On 2 August two papers on the origin of monogamy in mammals were published in PNAS and Science. These papers got me excited because: 1) the evolution of monogamy is a very cool topic, 2) they are an illustration of how to hone in on a great topic for a senior seminar paper, and 3) they are a great illustration of the challenge of close reading of primary science texts. I’d like to address each of these issues in turn, but I’ll probably spend more time on 2 and 3 as the blogosphere has already covered the content of these papers extensively (see links at the end of this post).
Unlike in birds, monogamy is relatively rare in mammals (~9%). Three main hypotheses have been forwarded to explain those rare cases of monogamy: 1) male parental care increases survivorship of offspring, 2) non-overlapping ranges of females leads to males defending a single female, and 3) protection from infanticide. Interestingly, these two papers came to different conclusions. Opie et al. conclude that monogamy evolved as a defense against infanticide, while Lukas and Clutton-Brock conclude that low female density (and male guarding) is the cause of monogamy. These kinds of conflicting results are exactly what make for a great senior seminar topic. As with all writing, your senior seminar paper should be making an argument. Arguments are much more interesting where competing hypotheses still exist and evidence has been generated both for and against these hypotheses.
Of course, these active areas of debate really require you to read the texts closely. Do no ‘trust’ the analysis of someone in a review article. Do not stop at the abstract. Let me illustrate with how I approached reading these two papers with contradictory conclusions. First, I had to spend a lot more time on the methods and really working through the figures than I would for something in my research field. In fact, I actually had to delve into supplementary materials available on-line (more and more information is being moved out of the article and into supplementary material these days). I spent a frustrating long time trying to understand how the figure in Opie et al. actually illustrated their results. After my close reading, I tried to assess why these authors came to such different conclusions. They both used a phylogenetic approach to address their questions although their statistical approaches were somewhat different. Their datasets, however, were quite different. Opie et al. focused solely on primates and examined 230 species, while Lukas and Clutton-Brock examined 2534 mammal species. They also scored mating systems differently. Opie et al. had only two states: monogamy or polygyny whereas Lukas and Clutton-Brock had three states: solitary, monogamous, or group living. In the end, I was more convinced by the Lukas and Clutton-Brock argument. Perhaps it supported a stance I already had, but I also felt their classification of mating systems and their much larger data set allows for broader conclusions. I had a hard time accepting that infanticide selects for monogamy when some of the highest rates of infanticide are actually in polygynous/polyandrogynous species. This debate is clearly not over, and biologists in the field seem split in terms of whose evidence is most compelling. Great fodder for a senior seminar topic!