I just started Robert Sapolsky lectures series on Youtube on Human behavior biology, and on the second lecture, at this point, he is explaining how evolutionary biology can be used to predict lots of animal behaviors just through the differences on the skull size of adult males and females.
He considers two groups of primates, one in which the skull of the adult male is quite bigger than the female and the other where they are about the same size. He then asks the student: "which group would display higher male aggression?" I am lost at this point. How can the size difference alone be used to answer that question? The students answer the question: "the first group (in which the males are bigger)", and the reason provided is that their body is built for it. Why and how?
Following up, the next question is: which of the species has more variability among males in reproductive success? The answer provided: "obviously, it is the first one because the males are aggressive for a reason, and that is they are competing for reproductive access." Couldn't it be that the second group had a biological variation in sperm productivity, that greatly outmatched the fight for reproductive access of the first group? I mean, how can it be this easy to conclude such a complicated process? Shouldn't you carefully consider millions of other things before concluding that one group will have higher reproductive variation simply because of differences in the size of the skulls?