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In the Science Times today, an essay by Marlene Zuk:

In short, we have what the anthropologist Leslie Aiello called paleofantasies. She was referring to stories about human evolution based on limited fossil evidence, but the term applies just as well to nostalgia for the very old days as a touchstone for the way life is supposed to be and why it sometimes feels so out of balance.
As an evolutionary biologist, I was filled with enthusiasm at first over the idea of a modern mismatch between everyday life and our evolutionary past. But a closer look reveals that not all evolutionary ideas are created equal; even for Darwinians, the devil is in the details. The notion that there was a time of perfect adaptation, from which weve now deviated, is a caricature of the way evolution works.

The topic is a fairly old one – the idea that we are adapted to the Pleistocene can’t literally be true. She hits on the reasons very well: (a) the Pleistocene encompassed huge temporal and ecological variability, so that no human population was ever optimally adapted to any given time or place; (b) various historical and structural constraints make such optimization impossible; and (c) we’ve been evolving rapidly for the last few thousand years. Her dates are off for scavenging versus hunting (probably Early Pleistocene at least, not 50,000 years ago) but she gets the lactase story right in a remarkably concise way.

And I like her ending:

This isnt to say that we wouldnt be better off eating fewer processed foods. And certainly we have health concerns that never struck our ancestors. But we shouldnt flagellate ourselves for having modern bodies, and we shouldnt assume that tweaking our diets or our posture will rescue us from all our current ills. Thats just a paleofantasy about the future.