...in those shorter average lifespans, but even those who lived to adulthood still often died young by modern standards.
From https://www.sciencenews.org/article/living-longer-comes-easier:
Despite what the fashion magazines tell you, 40 isn’t the new 30. Seventy is.
A new study finds that humans are living so much longer today compared with the rest of human history that the probability of dying at 72 is similar to the death odds our ancestors likely faced at 30.
A few people in our "all natural" past did indeed live into their sixties, seventies, occasionally beyond, but even from a standard of mortality as measured during adulthood (rather than from birth) this was a far more rare thing.
And yes, the better sanitation that comes along with understanding the germ theory of disease, and other medical advances, are a big part of where we get our current lifespans. Further, also as you mention, there's the modern availability of food that makes starvation and large calorie deficits (at least in wealthier countries) much less common.
Yet still, even given all of that, how large an advantage could an "all natural" diet be, and how truly terrible could today's processed food and preservatives and artificial flavors be, if such great increases in lifespan came along at the same time those things came along?
Is there solid evidence that we'd be living on average into our late nineties if we ate like a well-supplied non-starving cave man ate? Is there any evidence that if cavemen ate at McDonald's they'd have had average lifespans only in the teens instead of the twenties?
Don't get me wrong. I think there's a lot to be gained by being more careful about what we eat, not just in longevity but in quality of life. All I object to is taking far too seriously grand oversimplifications like "Natural GOOD! Artificial BAD!". A long, healthy life as a commonplace phenomenin is itself one of the most unnatural things there can be, and I'm all for it.
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