Marlene Zuk, author of RIDDLED WITH LIFE, essay in New York Times

The Evolutionary Search for Our Perfect Past
By MARLENE ZUK
New York Times, January 19, 2009

Remember when life was simpler, and diets weren’t full of processed food and chemicals? No, not the 1950s. Increasingly, we are developing nostalgia for a much earlier epoch: the Pleistocene, when humans lived in small hunter-gatherer groups and didn’t worry about high cholesterol.

Although the box-office lure of skimpy fur garments cannot be underestimated, movies like “10,000 B.C.” are popular because they appeal to our sense that life used to be more in sync with the environment. A recent cartoon shows one of those evolutionary progressions — ape to man walking upright to man slouched over a computer — with the caption “Somewhere, something has gone terribly wrong.”

Maybe our woes arise because our Stone Age genes are thrust into Space Age life. That beer gut? It comes from eating too many processed carbohydrates; our bodies evolved to eat only unrefined foods, mainly meat, and we get out of kilter veering from our ancestral diet.

Food allergies and digestive woes? We, like other mammals, aren’t meant to consume dairy products after weaning. When politicians fall from grace after committing adultery, some commentator will always point out that such behavior has evolutionary roots: weren’t the best procreators alpha males with roving eyes?

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 we’ve now deviated, is a caricature of the way evolution works.

First, when exactly was this age of harmony, and what was it like? Scavenging, or eating the carcasses of dead animals left by (or stolen from) predators like lions, was probably replaced by active hunting and accumulation of wild plants about 55,000 years ago, and agriculture seems to have begun a mere 10,000 years ago. We did a lot of different things during each of these times.

How much of the diet during our idyllic hunter-gatherer past was meat, and what kind of plants and animals were used, varied widely in time and space. Inuits had different diets from Australian aboriginals or Neotropical forest dwellers. And we know little about the details of early family structure and other aspects of behavior. So the argument that we are “meant” to eat a certain proportion of meat, say, is highly questionable. Which of our human ancestors are we using as models?

But the difficulty with using our hunter-gatherer selves as icons of well-being goes much deeper. It is not as if we finally achieved harmony with our environment during the Pleistocene, heaved a sigh of relief and stopped.

Instead, evolution lurches along, with successive generations sometimes unchanged, sometimes better suited to their surroundings in some ways but not others. At any one point, adaptations take place: individuals who can endure heat or cold or famine leave more offspring than their less hardy counterparts. But there is no one point when one can say, “Voilà! Finished.”

Did our cave-dwelling forebears feel nostalgia for the days before they were bipedal? Were hunter-gatherers convinced that swiping a gazelle from a lion was superior to that newfangled business of running it down yourself? And why stop there? Why not long to be aquatic, since life arose in the sea? For that matter, it might be nice to be unicellular: after all, cancer arises because our differentiated tissues run amok. Single cells don’t get cancer.

You might argue that hunter-gatherers were better adapted to their environment simply because they spent many thousands of years at it — much longer than we’ve spent sitting in front of a computer or eating Mars bars. That’s true for some attributes, but not all. Evolution isn’t the creaky old process we used to think it was. Increasingly, scientists are discovering that the rate of evolution can be fast (sometimes blindingly so) or slow, or anything in between.

Marlene Zuk is a biology professor at the University of California, Riverside, and author of “Riddled with Life: Friendly Worms, Ladybug Sex and the Parasites that Make Us Who We Are.”

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