[plasticeagle]

I suppose that must depend on one's definition of "substantially". Human's haven't changed "substantially", and neither do new breeds of dogs and cats.

Besides which, why does it matter that Humans may or may not be fit according to old criteria? Whatever they might have been.

[killerstorm]

People in the past could survive and procreate without modern medicine (basically without any medicine at all as doctors could do very little 200 years ago) with ~50% success rate. I'd suspect this rate is already lower now, and it might matter in multiple ways