Friday, June 27, 2014

Paleo Made Simple

I recently read Marlene Zuk’s Paleofantasy: What Evolution Really Tells Us about Sex, Diet, and How We Live. I found nothing really surprising in it, but maybe that’s because I know a thing or two about evolution. For many people, this book should come as quite a revelation. It is a good book and I highly recommend it.

I don’t follow fads very closely, but apparently “paleo” is a big fad these days. The idea is that (1) humans evolved under Paleolithic conditions, to which our bodies are very closely adapted, and (2) that very little evolution has occurred since that time. Therefore, to be healthy and happy, we have to live like cavemen or (3) at least like hunters and gatherers.

Zuk takes aim at all three of these assumptions. The first assumption is that humans are very closely adapted to Paleolithic conditions. Zuk explains that there is quite a range of Paleolithic conditions; different prehistoric peoples lived in very different ways. Therefore there is no single Paleo diet that is best for us. Some Paleo faddists think we should only eat meat, others only vegetables; but in reality our Paleolithic ancestors ate both, with different groups having a different balance of local foods. Of course tropical people ate more fruits, and the natives of the steppes consumed more meat and dairy. Some of them chased down wild animals to eat, some of them didn’t. Zuk points out that the human body has a lot of developmental plasticity. If we grow up barefoot, our feet adjust to walking on hard ground; if we grow up wearing shoes, our feet adjust to them. A Paleo faddist who says that we really should go barefoot because cavemen did is ignoring the immense ability of the human body to adjust to conditions.

Secondly, Zuk gives numerous examples of recent genetic changes in the human species, such as the ability of some people to tolerate lactose, and of some people to digest more starch. Both of these adaptations are genetic and have occurred since the beginning of herding and agriculture.

Thirdly, Zuk points out that we cannot really be sure what primordial hunter-gatherer cultures were like. We cannot look at modern hunter-gatherer cultures and assume they are just like our Paleolithic ancestors. While this may be a reasonable assumption for the Hadza of Africa, it is probably not for the natives of the Amazon forest. Apparently only a thousand years ago there was an Amazonian civilization. Although most of the soil in the Amazon basin is very poor, the people of this civilization built up rich soil in some places (terra preta de Indio), and the archaeological remains of their cities are just now being studied. Today’s “uncontacted” tribes may have been refugees from collapsed cities (a collapse perhaps stimulated by smallpox) rather than the pure descendants of hunter-gatherer cultures. Even the San and Hadza have had a long history of contact with agricultural societies, primarily the Bantu tribes, long before European contact.

Of course, at a very basic level, our bodies are adapted to prehistoric conditions. This is undeniable. It is just that we cannot use this as a detailed prescription about how best to live. Instead, awareness of our Paleolithic heritage should lead us to some essential generalizations. Should we run long distances slowly or short distances rapidly? Barefoot or not? What we really need to do, says Zuk, is just to get up off of the couch. What should we eat? Meat or not? Raw or cooked? Clearly we are not adapted to a diet of Twinkies and coke. But perhaps the Paleo prescription that we should follow is the simple prescription from Michael Pollan: Eat food, not too much, mostly plants.

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