>Literally, hundreds of people (elite marathoners, a few ultra marathoners, cross country skiiers) out of billions of people are bumping up against physiology

The human race didn't fight tooth and nail for 40,000 years to give everyone education, a code of laws and civilization, safe lives that include both work and leisure, so that I could bump into the limits of my physiology. How is that a normative goal?

There are no mountain lions chasing me whose escape pushes me to the limits of human physiology - and I for one prefer to keep it that way!