[luk_hol]

That's interesting. But do you have some data to back up your claim or is this just your guess? Because there are two effects at play here: on one hand a kind of a survivorship bias that you mention and on the other hand a positive effect of a healthier environment on a human body. These go against each other and I don't find it obvious to see which one is stronger.

After a quick search I would say the latter is more important here: what we observe from the bones are things like a quality of nutrition (e.g. vitamin deficiencies) or effects of some illnesses. Inadequate nutrition signals poor living condition and illnesses affect even the most "gifted" individuals (don't forget that hardship selects also for other traits than just a good immunity).