> Humans are built for constant labor. We're the endurance-running champions of the animal kingdom That is a contentious assertion. Yes, perhaps we can go for

> Humans are built for constant labor. We're the endurance-running champions of the animal kingdom That is a contentious assertion. Yes, perhaps we can go for longer distances than other primates, but it doesn't mean that this has anything to do with our ideal exhaustion, nor that it was something we did regularly, nor that it is free of negative side effects, nor that other primates couldn't do it if we could design some (very unethical) experiments. Experiments on the health effects of high intensity short duration exercise are very compelling. I agree with you that we are not generally adapted to modern lifestyles, but there are a whole host of other factors to insomnia in that grab bag (terrible diets eaten year round, artificial light, social isolation).