Laura Darrell

Among the current dietary and lifestyle fads is the paleo diet--the idea that we evolved to eat like our paleolithic ancestors, and have had too little time to evolve to suit our current lifestyle and diet. Marlene Zuk looks at the actual science, including what our paleolithic ancestors really ate, and how long it really takes for natural selection to spread changes in what foods we can digest and how.

I should say up front that Zuk isn't against eating a paleo diet, if that's what works for you. What she's arguing against here is the idea that paleo, or any other highly specific diet, is or can be the One True Way.

The archaeological evidence says our ancestors were eating grains and root vegetables much earlier than previously thought. Also that just like contemporary humans, populations in different areas ate different things, based on what was available locally. The idea that paleolithic humans only ate meat, fruits, and maybe some non-starchy vegetables is as unfounded as the idea that eating meat is "unnatural" despite the ample evidence that our ancestors have been eating meat for at least two million years.

What we do see when we look at modern humans is that, whether living in "developed" countries or maintaining something close to a hunter-gatherer lifestyle, diets vary widely depending on what's readily available and culturally acceptable to the people doing the eating. Hunter-gatherers in coastal regions eat a lot of fish. More inland hunter-gatherers eat a lot more plant foods, but the animal foods they eat are a lot more likely to be mammals than fish. Most Western populations don't make much, if any, use of insects as food, though they are valued as a tasty, convenient source of protein in many other cultures.

The evidence we do have for paleolithic hunter-gatherers, as far as we've been able to find it, is that they had similarly diverse diets, based on what was available in their regions.

The other part of the equation is, how fast can we evolve changes in what we can easily digest? Here, the evidence is that the paleo enthusiasts, as well as other, differently extreme, diet advocates, have it wrong.

Consider milk. Most people reading this review will have grown up in a culture that regards milk as a healthy food. Most will also be aware of some people who have "milk intolerance," the inability to digest milk because their bodies stopped manufacturing the necessary enzyme, lactase, in infancy.

What you may or may not realize, depending on your background, is that ending lactase production after weaning is normal, in humans and pretty much all other mammals. Adult milk consumption is weird, really.

But in people descended from populations that had a pastoralist lifesstyle--following herds or keeping herds of cattle, horses, goats, etc., eating milk and milk products is normal, while in places that have been long-settled and long-civilized, such as China, the mammalian norm of hardly anyone producing lactase after weaning is the norm for the human populations there, too.

In populations where people lived a pastoralist lifestyle for a long time, that minority of the original population who kept producing lactase into adulthood were more successful, and had more offspring, and that mutation became widespread. And this happened fairly quickly, starting no more than about 7,000 years ago.

What's even more interesting is that while the mutation that continues lactase production is the most common route to adult milk consumption, in some populations, a different path to the same result occurred. Zuk describes populations that, instead of producing lactase as adultss, seem to have a different mix of gut bacteria. Gut bacteria do a lot of the work of digestion, and these populations have a mix of gut bacteria that helps them digest milk.

My discussion of this is not nearly as interesting as Zuk's. If I've interested you at all, or touched on things you think could be interesting if discussed better, do read the book.

Highly recommended.

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