There tend to be two contradictory, mutually held and widespread beliefs about humans before industrialization-one, that everyone was healthier, because of all that exercise, fresh air, and natural selection, the other that lives were brutish and short because they didn’t have modern medicine and indoor plumbing.

I assume that recent increases in average lifespan (which seem to be well documented enough) really are probably due to the better nutrition and less stressful environments of modern life. But if that’s true, then it doesn’t seem unreasonable to suppose that something close to contemporary lifespans were possible for those of our ancestors who were lucky enough to live in conditions that nearly approximated ours. It just happens those conditions were rarer, and so fewer people enjoyed their benefits.

If we had better data on the percentage of people who died in their sleep after living long lives, we could get some sense regarding what the optimal lifespans were before the 20th century. But I suspect getting information like that is going to be a real pain in the butt.

In addition to the increasing prevalence of environmental toxins, another idea occurs to me. Perhaps the r…eduction of infant mortality has released the evolutionary pressure on cancer prevention. For example, more people are near-sighted now than they were 1000 years ago not (just) because our lifestyle causes myopia but because the invention of eyeglasses allowed the otherwise blind to survive and reproduce. Similarly, it is possible that the same childhood ailments (or genotypes susceptible to those childhood ailments) are associated with increased propensities for cancer.

That’s my hypothesis of the moment, anyway :)