For some time, the “Paleo” lifestyle has been due for a decent critique from the perspective of growing evidence about the rapid rate of human evolution. Humans have evolved markedly since the dawn of agriculture, with adaptations ranging from disease resistance to the improved ability to digest starch. So when I heard of Marlene Zuk’s Paleofantasy: What Evolution Really Tells Us about Sex, Diet, and How We Live, I was looking forward to that critique being provided.
And Zuk certainly provides a critique. She relentlessly pulls apart the ideas that we are well adapted to the Paleolithic environment, or that rapid environmental change means that there is mismatch between the environment and our genes. As Zuk points out, evolution does not result in stasis and there is no point at which we are ever completely adapted to our environment. We will always be a collection of bootstrapped responses to changing conditions.
However, Zuk’s critique was not the one I was hoping for. As was the case for the promotion pieces and reviews that I read before reaching the main course, Zuk parades a series of straw men rather than searching for the more sophisticated arguments of Paleo advocates. Many chapters begin with misspelled comments that Zuk found under blog posts. While Zuk shoots the fish in the barrel, the more interesting targets are not addressed.
In a Nature review, John Hawks suggests that Zuk’s use of the term ‘fantasy’ is a reference to hypothesis forming, where we play with hypotheses and try to falsify them. I tried to read the book in that light, but it is hard to do. Zuk appears so keen to throw Paleo-enthusiasts under the bus that she does not give many of the hypotheses the thought that they deserve. At times Zuk seemed almost desperate to find someone to be on the other side of her debate, such as when she chose Ryan and Jetha’s Sex at Dawn as her punching bag for her discussion of sex differences, even though Ryan and Jetha are almost on their own with their thesis. Where she did write qualifiers about not everyone believing in the straw man that she was about to dispatch (which was often), she would proceed to torch the straw man as though the just acknowledged view did not exist.
Take the chapter on diet. Zuk points out that many humans have evolved lactose tolerance. Those with a longer history of agricultural diets have genetic adaptations to allow them to digest starch more efficiently. Even the foods we eat have evolved, with potatoes formerly bitter and lumpy, and corn having a shape and size more like a stalk of rice. But these are points most Paleo-advocates would happily concede. They are not seeking a historical re-enactment. Their argument is not that we have not changed at all, but that the changes have not been enough to make a diet full of grains and sugar superior to a diet of meat, nuts, fruit and vegetables. Whether that is the best diet could be the subject of an interesting debate (i.e. testing the hypothesis), but this is not the argument that Zuk engages with.
Moving to a more substantial point, a review in Evolutionary Psychology nicely summarises Zuk’s mismatch argument as being at three levels: there are no mismatches as all species are adapted to past environments, not current ones; even if mismatches occur, we are not in a position to understand them; and the mismatch perspective has not proven beneficial.
On the first of these, Zuk pushes too far by highlighting cases of rapid evolution while ignoring cases where mismatch does occur. Her description of the evolutionary bootstrapping that must occur when organisms encounter new environments points to the potential of mismatch. Zuk’s arguments about the difficulty in understanding mismatches leans towards saying it is all too hard, and not engaging in the sort of hypothesis testing that Hawks refers to. And on the point that the mismatch hypothesis has not proven useful, there are times where Zuk shows just how useful a mismatch perspective might be. She acknowledges that the high sugar content diet of the last 50 years is not something we are matched to, and provides some interesting points on barefoot running and the evidence of the cost of cushioned shoes. The mismatch between current and past physical activity (accompanied by the suggestion that people should simply “get off the couch”) is almost too obvious to mention.
Having said all the above, I still enjoyed the book. There is a lot of punchy writing, many important research results and underneath her advocacy style, some interesting questions about diet, exercise and other “Paleo” lifestyle features. However, my instinct is that many people won’t see these points due to Zuk’s approach, which will lead to a less interesting debate than we could have had. I suppose this post is further evidence of that.
*To avoid getting completely derailed by style instead of substance, next week I’ll write a post on what I consider to be the most interesting questions about recent evolution and the Paleo lifestyle (read it here).