The Caveman Controversy
In her new book, Paleofantasy, Marlene Zuk dared to debunk a lifestyle that advocates eating, exercising, and even mating like our ancestors. Now the outspoken insect-sex researcher has adversaries, who say she’s the one whose thinking needs to evolve.
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For Zuk, food is worth discussing mainly as a window into new discoveries in human genetics and evolution that show how our genes have changed and the speed at which those changes have occurred. A mutation within the past 10,000 years, for example, gave adults the ability to digest the lactose sugar in milk; today, about a third of the population possesses that gene variant, raising doubts about the Paleo diet’s stance against dairy. “There are people who argue from a Paleo diet perspective that we shouldn’t drink cow’s milk because we didn’t evolve to drink milk from cows,” says Michael Wilson, an evolutionary anthropologist at the U of M. “That’s a fair argument to make for cats. You shouldn’t give a cat a lot of milk to drink because they haven’t evolved to drink milk as adults. But people in populations that have had dairy animals for many generations have evolved to drink dairy from their animals. It’s one of the examples of human evolution still going on.”
Strict Paleo eaters also eschew grains and sometimes even potatoes, but some evidence suggests that tubers were an important source of carbohydrates as far back as the time of Australopithecus, the genus that lived before the Homo line emerged, Wilson says. According to archaeological remains, Zuk writes in her book, early people in Europe appear to have mixed water with the flour of ground-up plants to make a bread-like product. And recent gene shifts have given people who live in carb-reliant cultures the ability to digest starches more quickly. Compared to hunter-gatherer groups who rely mostly on meat, people in places like rice-eating Japan have more copies of a gene that helps them break down starches.
Even if you wanted to eat like people did in the Stone Age, Zuk argues, it would be impossible. The Paleolithic period lasted nearly two million years. During that time, humans lived in many different climates and terrains, and their diets varied widely. Depending on where they lived, some groups did a lot of hunting. Some did more gathering. Some ate a lot of fish. Some had more access to fruit. That variety makes it hard to pick one ancestral diet most worth emulating. Meanwhile, the animals and plants that we eat have themselves changed drastically through breeding and natural selection. “The ancestral potato, for example, was a bitter, lumpy root a fraction the size of the average Idaho baker,” Zuk writes. “What we now know as corn started out 9,000 years ago as a Mexican grass called teosinte, with a shape and size more reminiscent of a stalk of rice than of the fat yellow kernels on a cob.” Many of the foods our ancestors ate, in other words, no longer exist as they knew them.
Often overlooked by vehement Paleo proponents are Zuk’s chapters on high-altitude adaptations, cancer in ancient people, barefoot running, variations in the stickiness of earwax, the development of resistance to malaria, and a discussion of the tolerance different cultures have for letting their babies cry. Everywhere you look, there are examples like these, Zuk writes, of humans adapting to new challenges—sometimes through changes in behavior, sometimes through changes in genes, and sometimes through a combination of the two.
Evolution is not simple, adds John Hawks, a paleoanthropologist at the University of Wisconsin, Madison, who agrees with Zuk that the process is far from over. “When I was a student, most professors assumed that humans had really stopped changing 100,000 years ago,” he says. (Other experts have made similar arguments on scales ranging from 10,000 to a million years.) “Now, we know we’ve been changing much faster in that period than we ever did before. We’ve never been perfect. We’ve never stopped changing. We are absolutely still evolving.”
New genetic tools are revealing so many new examples of evolution happening at a rapid clip that Zuk had trouble letting go of the Paleofantasy manuscript; new studies kept coming out that she wanted to include. But even as our genes change, Hawks says, they don’t necessarily work as a blueprint for determining how our lives will go. That’s where arguments that claim we are designed to live a certain way fall flat. “Humans are behaviorally flexible and culturally flexible, and the choices we make are often determined by what people around us are doing,” he says. “If there’s one thing about humans, it’s that we surpass our genetics. We do things you wouldn’t predict from genetics. To say today that we should do something because that’s the way it was done in the past doesn’t make sense.”
Yet neither should we necessarily do something—drink milk, for example—just because we now have the genes to do it. Paleo-eating might suit some people regardless of their genetics; there is unlikely to be a single diet that works best for everyone. “For a long time, there was a common notion that evolution happens slowly, that evolution is progressive, proceeding toward a particular goal, that anything that’s more recently evolved is necessarily better adapted in some way, and that humans are the pinnacle of evolution,” Zuk says. “In a lot of ways, those are wrong ideas.”
Emily Sohn writes about health and science for the Los Angeles Times, Science News, and other national publications. She lives in Minneapolis.