Marlene Zuk’s Paleofantasy: what we (don’t) know about our ancestors

by Matthew R. Francis 

“[T]he first thing you have to do to study 4,000-year-old DNA is take off your clothes.” So begins Paleofantasy (W. W. Norton & Co., 2013), Marlene Zuk’s examination of the idea that human beings evolved for a lifestyle very different than the one we exhibit today. Zuk – who is professor of ecology, evolution, and behavior at the University of Minnesota – is particularly concerned about the version of evolution presented by advocates of the “paleo lifestyle”. The result is an often witty, sometimes problematic, but ultimately important look at a movement that claims the mantle of science but may not be quite as scientific as it seems.

The paleo lifestyle refers to the paleolithic: the “old stone age” of humanity, before the rise of complex tool use and widespread agriculture, yet still within the span of Homo sapiens, the modern species of humans. While different versions exist, the basic premise of the paleo lifestyle is that we adapted to the paleolithic world, especially its diet, and that our modern technocentric lifestyle is the direct or indirect cause of any number of ills. By returning to the paleolithic lifestyle, while retaining valuable modern contributions like medicine, we can all be healthier and happier.

I doubt many would argue that the average American today is living optimally. (I’m from the United States, and from what I can gather, the paleo movement is largely American, so please forgive me for focusing on my own nation.) As a group, Americans exercise too little and eat too much, and our diet is pretty bad: high fat, salt, and sugar content, highly processed to remove fiber or other nutritive substances. This sedentary and nutrition-poor lifestyle can lead to many health problems: heart disease, type II diabetes, and so forth.

Paleo advocates hold that we should return to the types of foods our ancestors ate, and participate in activities similar to those they performed. We shouldn’t eat pasta or Big Macs, but instead follow a diet high in meat content, fruits, and vegetables. We shouldn’t be couch potatoes or run marathons, but we should do varied intense short-duration exercises, possibly even while barefoot. The idea is that modern humans arose some hundred thousand years ago, but cities, agriculture, and other technology-based innovations came much later – too late for us to adapt.

Those positions sound reasonable on their face, but they also fall into the realm of testability. In Paleofantasy, Zuk examines the various arguments for and against the paleo view of life, from genetics, evolutionary biology, and anthropology perspectives. As the title indicates, she is not sympathetic to it: the paleo lifestyle is not based on real scientific evidence, but rather a mythic and often romanticized view of how our ancestors lived. During the paleolithic era, humans followed a variety of lifestyles, some of which we know from archaeological evidence, some which we may never be able to reconstruct thanks to scant remains. And far from being the same animals we were 40,000 years ago, humans continued to change, adapting to new environments and evolving new features.

As you would expect from a professor of evolution, Zuk’s chapters on genetics and evolutionary relationships are strongest, while some of the more lifestyle-centric and anthropological sections are a bit less focused. Part of that is the nature of the evidence involved, of course, but I think it may also be partly an inherent problem in addressing an entire worldview, one which the author doesn’t share and isn’t particularly sympathetic to. To put it another way: Zuk’s critique of the paleo lifestyle is strongest when she has specific scientific objections and weakest when she falls back on bemusement. However, the science generally takes the forefront, making Paleofantasy a very good counterbalance to claims that the paleo lifestyle is the one true science-based way to live.

The Paleo Diet and the Clock of Human Evolution

If you’re like me, your primary introduction to the paleo lifestyle is some version of the Paleo Diet. As with other diets, the Paleo Diet comes in several forms, and adherents choose it for a variety of reasons. The promise of weight loss and improved personal health top the list as usual, but as with the rest of the paleo lifestyle, the premise of the diet is a return to a generally healthier mode of existence.

The basic Paleo Diet is pretty simple: unprocessed (or minimally processed) meats, fruits, nuts, and vegetables that can be eaten raw. Grains like wheat, rice, and corn – which require agriculture and cooking – are out, as are beans, other legumes, and potatoes. Cooking itself is OK, so long as the foods are edible without it: you can eat your steak well-done and fry your onions. However, dairy products like cheese are not allowed, and even grain-based products like beer may be forbidden. This can lead to a bit of hairsplitting from an outsider’s point of view: for example, tea is fine, but coffee (which requires roasting) is not. Zuk mentions a discussion on a paleo website over what maximum size of sweet potato is allowable, since smaller ones can be eaten raw, while larger specimens need cooking.

Zuk is primarily interested in examining whether the paleo diet is an authentic representation of what our ancestors ate, but also whether humans could have adapted to a different diet over a period of thousands of years.

And certainly, eating mainly lean meat and few or no processed foods may well be healthy for at least some people, particularly when contrasted to a diet of Cheetos and Coca-Cola. The question is whether the various forms of the paleo diet really do replicate what our ancestors ate, and further, whether that should serve as a guide for us in the twenty-first century. (p. 115)

Certainly that’s true in the case of lactose tolerance: the ability of many people in India and Europe to digest cow milk into adulthood. The better term is actually lactase persistence, lactase being the enzyme infants use to digest milk. Most humans stop producing lactase before adulthood, but based on archaeological and genetic analyses, some populations evolved the ability to keep making the enzyme throughout life. That ability arose within the last 10,000 years or so, which counts as a relatively recent development. Lactose persistence isn’t alone: Zuk also catalogs the evolution of blue eyes, ability to live at high altitudes, and malaria resistance.

Zuk’s point is that if humans can evolve to eat foods our ancestors could not, then there’s no need to believe that only an ancestral diet is healthy. Sure, you can eat too much cheese (not that ahem I have any experience of that), but just because Oog and Grunk didn’t or couldn’t eat bread doesn’t mean modern humans shouldn’t. It’s also problematic to think that every human ate the same way before the rise of agriculture, even assuming that farming was something that spread relatively rapidly.

As archaeologist Tim Denham and his colleagues point out, “Early agriculture is not a demarcated ‘all or nothing’ lifestyle that can be clearly mapped across space and tracked through time.” As with all other processes in evolution, the move to a different way of obtaining food came about in fits and starts, with some human traits adapting well to the changes and others not so much….(p. 48)

What evidence there is for paleolithic diets shows that humans ate foods according to the environment in which they lived, with different balances of meats, fruits, and vegetables.

I want a brave man, I want a cave man

Things are even less clear when paleo advocates discuss parenting and other aspects of family life (co-sleeping of parents with infants, etc.), for which we have no evidence. Some paleo lifestyle adherents even write the kinds of things that wouldn’t sound amiss on a fundamentalist website: decrying women working outside the home, the evil influence of pop culture on children, and calling for a return to 1950s values in the name of “paleo” life. (How they reconcile the idealized 1950s suburban lifestyle, with its dependence on cars and processed convenience foods, with the paleo ideals, I’m not entirely sure.)

It’s also entirely plausible that our ancestors may not have eaten an optimal diet: they were restricted to the foods available, which doesn’t mean they’re the best possible foods. They may have chased prey quickly (or been chased) or pursued wounded animals on foot to wear them out, but that doesn’t mean either type of “exercise” is best for us today – or the only possibilities that could work. Looking at the few remaining hunter-gatherer societies provides little help: even if they remain relatively isolated from technologically modern cultures, they don’t give us a picture of how things were 10,000 years or more ago. Even that assume these hunter-gatherers didn’t possess, then give up, agriculture, which may be the case for some. Even if humans were genetically stable, cultures change on an extremely rapid timescale. And unlike genes, environmental alterations to a culture can be passed down from generation to generation: humans learn new behaviors at a much faster rater than internal change.

It’s a natural tendency to think that, because modern life has many problems, returning to a pristine state in the past would cure all of that. Agriculture, industrialization, and high population density have serious disadvantages, with widespread disease, famine, and the kinds of poverty only available in overcrowded urban environments. However, as Zuk emphasizes, science doesn’t provide us with an idyllic view of paleolithic life either. No doubt survival was more dependent on local conditions than it is today, when agriculture and shipping can partially make up for local drought or flooding. Cancer – often presented as a modern ill, even one for which dietary choices are to blame – likely existed at similar rates to today (with a few specific exceptions like lung cancer linked to tobacco), but would not have been as survivable.

Paleolithic life may not have been as nasty, brutish, and short as Thomas Hobbes would have it, but it seems to this physicist that any “golden age” of humanity must still lie in the future. Rather than projecting our paleofantasies onto the past, we should – following Zuk’s example – be clear-eyed about how our ancestors lived, both the good and the bad aspects. Certainly we might be able to improve our lives today by studying the paleolithic, but – in the best traditions of humanity – we should take what works and discard the rest.

“Golden Age” by TV on the Radio