One might wonder, if exercise takes energy, why haven’t people evolved to no longer need exercise? My theory is that it’s because exercise has always been there and it was potentially useful. The energy was spent anyway, and since it was a constant, the body found uses for it, rather than evolving new mechanisms to accomplish all the things that exercise does for us.
I like the analogy of an ancient, thousand year old city with a river running though it. Over time, the inhabitants would develop many uses for the river and come to depend on it. They might wash themselves, their clothes, transport goods, catch fish, irrigate, siphon water energy and so many other things from that river.
Now, imagine that river suddenly dries up. The city would be in very bad shape as they are not adapted to the absence of the river. The city may dwindle as people die and migrate, though over some long period of time, the remaining inhabitants may adapt to new practices to thrive without the benefits of the river.
I think exercise with humans is much like this. Exercise has always been there, but has suddenly (rather abrupt, relative to the long evolutionary timeline) stopped, and therefore all those physiological and mental mechanisms that had made use of exercise are now suffering.
Will humans ever evolve to need less exercise? Perhaps. I would guess that some of that has happened already – that some individuals are healthier despite lack of exercise whereas others need more. I also suspect there could be more people tolerant of lack of sleep, slavery, clothing and other characteristics of civilization than existed in the stone age.
However, when you talk about any kind of human evolution, the evolutionary game has gotten very strange and complex with governmental, medical, societal changes and complexities that have arisen over the last century. The genes that perpetuate the most now may be way different than did as recent as the late 1800’s. Evolution is now so subject to ever-changing societal intervention that it blows the conventional Darwinian stereotypes of “survival of the fittest” out of the water, as “poorly fit” individuals are medically, culturally or governmentally enabled to reproduced at greater rates than they would have ever in human history.
