Thesis #3. Health and adaptation thus reflect the action of natural selection on a population in its previous environments, not its present environment, when these differ.
For the purpose of re-founding medicine scientifically, theses 2 and 3 direct us to pay particular attention to the sequences of environments that humans have been exposed to during our evolutionary history. It is fanciful to suppose that, because our species has been in existence for several hundred thousand years of evolution, it is fully adapted to any environmental conditions that it might encounter.
And this point is still more profoundly important when we consider the extent to which our environments have been transformed over the last century of rapid technological change. Just four or five human generations are far too few to have given us adequate adaptations to our present environment. Instead, what adaptations we have, and thus the conditions under which our fitness is likely to have been maximized, reflect the impact of natural selection on our evolution prior to the advent of our present, highly technological, industrial environment.
Thus evolution by natural selection has supplied us with adaptations only to environments in which we have lived for many centuries. But this does not then immediately imply any simple or obvious set of inferences about how medicine can best manage human health or treat our diseases. For the action of natural selection is subject to still other limitations, well beyond the vagaries of environmental history.
Editorial from Rob – Sitting is in fact very bad for us – we are designed to be active and to move all day – here is some useful research about the costs of sitting
It is these further limitations on the action of natural selection that we turn to next.