We really are not optimal in any particular way. We started out as monkeys, and have done the best we could from a bad starting point. Turning the spine vertica

We really are not optimal in any particular way. We started out as monkeys, and have done the best we could from a bad starting point. Turning the spine vertical really did not work out well at all, and knees are unfortunate at best. Probably worse than all that is how we go all to hell when we don't get exercise. Cats can sleep 18 hours a day without ever getting out of shape. Bears can can get super fat and then sleep for months, and be fine. A lot of birds can go a week without drinking or eating, working out the whole time with no sleep or even rest breaks.