In the evolutionary battle for procreation advantage, muscles can be an advantage, but not cheap.
Because muscles come at such cost, Dr Gaulin thinks an evolutionary fight is going on between natural selection, which conserves metabolic expenditure and promotes longevity, and sexual selection, which willingly trades both for extra mating opportunities. This may explain why men have such a range of muscularity. In the past, the strong man would have had better mating opportunities in the short term, but the skinny guy who outlived him could have had just as much reproductive success over the course of his longer life.
The irony for the skinny guy is that the laws which protect him from aggression also make it less likely that the hulk will fight himself into an early grave. Modern medicine, meanwhile, means the hulk’s weakened immune system is less likely to expose him to lethal infection. Time, then, to get the weights out, and start pumping iron. [More]As usual, the outlook for guys in the middle is ambiguous.