Wednesday, July 25, 2007

Small teeth & sexual dimorphism?   posted by Razib @ 7/25/2007 12:23:00 AM

A Hunk's Dental Downfall:
When males and females were about the same size, so were their teeth. But in species in which larger males evolved, tooth size increased relatively little. Thus, females ended up with larger chewing surfaces for their size than did males, the researchers report in the September issue of American Naturalist. The team concludes that teeth probably didn't grow at the same rate as body size because males can successfully compete for females only in their prime. Once teeth wear down, they become ineffective, and the animal gets weaker and more susceptible to disease or injury. But that doesn't matter to these males, as once they are too old to beat out rivals for mates, there's no need to live a long life. When it comes to how many offspring a male can father, "it seems that compared to body mass, tooth size is relatively unimportant," says Joanne Isaac, a mammalogist at James Cook University in Townsville, Australia, who was not part of the study team.

In highly polygynous species males in their prime are the fathers of a multitude. These species' males enter into a winner-take-all lottery game when it comes to reproduction. It makes sense that these males wouldn't live that long. It isn't likely that they could greatly increase the fitness of their numerous offspring through parental investment simply because there might be so many of them. Male investment in humans makes some sense in the case where a typical man may have only a few children who survive to their reproductive years. Nevertheless, there is some reproductive skew within our own species, and the extent of that skew varies from population to population and across historical epochs. The reproductive outcome for the total population may remain the same no matter if it is characterized by a equilibrium of low risk & low yield male strategies, or high risk and high yield strategies, but the dynamics within the society are likely going to be very different. I am not convinced that our current low risk & low yield strategy (i.e., monogamous pair-bonding) isn't just a metastable situation, highly susceptible to disruption.