Paleo lifestyle trends are popular at the moment—but they are rooted in evolutionary myths, says evolutionary biologist Marlene Zuk of the University of California–Riverside. Her new book is Paleofantasy: What Evolution Really Tells Us About Sex, Diet, and How We Live.
Your book is about pseudoscientific ideas you call "paleofantasies." What are they?
They stem from the idea that evolution makes minuscule changes over millions of years, so we haven't had enough time to adapt to the modern industrial world—and that we would be healthier and happier if we lived more like our ancient ancestors.
Is there any truth to the idea that we haven't evolved fast enough to cope with modern life?
To some extent it is true. Our bodies are ill-suited for sitting at computers all day, for example. Because humans evolved in an environment where they were not crouched over computers, sitting that way all day is going to have ill effects. But it's more nuanced than that. Being bipedal has a lot of costs on the human skeleton, too. Should we all long to be quadrupeds? It just doesn't make sense.
What is driving the tendency to idealize the way ancient humans lived?
There is this caricature that organisms evolve until they get to a point when they're perfectly adapted to their environment, then heave this big sigh of relief and stop. Anything that happens to them after that is disastrous.
You see this attitude in what can be referred to as "paleo-nostalgia"—the notion that we were all better off before agriculture, or civilization, or the Industrial Revolution. It's not to say life has been unmitigatedly getting better. But it's more helpful and accurate to see that all organisms are constantly evolving. There has been no point in our past when we were perfectly adapted to our environment.
I'm not dismissing the idea that you need to look at our evolutionary heritage to think about what's best for us healthwise. But when you start plucking out pieces in an oddly specific way, you can run into trouble.
Are paleo diets, which usually involve eating lots of meat and avoiding grains or dairy, examples of this type of specific selection?
These are predicated on the idea that there was a certain way humans ate 100,000 or 15,000 years ago—the era people want to hark back to varies. I think everybody agrees that we evolved eating certain things and we're going to be very unhealthy if we subsist on Diet Coke and Cheetos. But it gets more complicated when you look at the details. Should we eat a lot of meat, less meat? Should we eat dairy?
How much do we know about early human diets?
We don't really know what they were eating. It's turning out that they may have eaten more starch and carbohydrates than we had realized. They also ate different things in different parts of the world. So it's hard to come up with this one perfect human diet that everybody was eating. Plus our genes have changed in the last 10,000 years. Lactase persistence—the ability to digest milk as adults—is the poster child for this. Our genes have changed extremely rapidly so that at least some populations of humans can digest milk into adulthood.
And just as with lactose, it turns out that in human populations that consume a lot of starch, there are more copies of genes that allow starch breakdown. All of this suggests that evolution is happening all the time and much more quickly than people think.
So is it possible to truly eat like our ancestors?
Trying to emulate what people ate 10,000 or 100,000 years ago is really difficult. Our foods have changed so much that virtually every item in a supermarket is drastically genetically different from its prehistoric equivalent. This is what humans do: We modify foods so that they become more palatable and digestible.
I'm not out to diss paleo diets. Clearly a lot of people who eat that way are happy with it and feel like they're healthy. It's almost certainly better than living off junk food. But it seems to me that decisions about what's going to be good for you have to be based on data, not just trying to eat what everybody ate tens of thousands of years ago.
Do you think the rise of these types of diets is a response to junk food culture?
Ironically one of our big problems in the developed world is an abundance of calorie-rich food. There is a lot of research on the "thrifty genotype" idea—that our ancestors evolved to deal with boom and bust food availability. If you're always in boom, it's going to have unexpected consequences for your health. That's a good example of how we need to consider evolutionary heritage when we think about food and how it affects our physiology. But that's different from saying we should eat exactly like our forebears.
What do you think of fitness regimes that advocate exercising like a hunter-gatherer?
There are people who argue that our ancestors ran mainly in short, sustained bursts: fleeing a predator or chasing down prey. As a result, they advocate brief spurts of high-intensity training. But there is also convincing evidence that our ancestors could run for sustained, marathon-like distances, which may have been selected for because it helps in what's called persistence hunting, where you run down prey until it drops from exhaustion.
As with food, to me the more interesting thing is not to try to model our exercise regimes on what early humans did, which we will probably never know for sure, but instead to use the limited data we do have as a jumping-off point and then develop ideas about how best to exercise using information from the here and now. The point is to get inspired by the past, not constrained by it.
What about the view that a lot of diseases arise because of the mismatch between our genes and modern lifestyles?
This is the idea of so-called "diseases of civilization." There have been enormous increases in Type 2 diabetes and autoimmune disorders. There are many diseases that have only arisen in the last few centuries or that seem to arise only among people living in first-world conditions. There are communicable diseases like measles that only happen when people are in groups of a certain size. Because of that, I suppose you could argue we should live in tiny villages and then we wouldn't get measles. To me a better solution seems to be the measles vaccine.
So you think that this logic about "diseases of civilization" can be taken too far?
Yes. There has been lots of discussion of cancer as a modern scourge, but this isn't supported by the data. It turns out that ancient remains show about the same incidence of cancer as we have, with the exception of lung cancer. This is tied to tobacco use, which obviously is more modern. But overall the data doesn't support the idea that we didn't get cancer until we started living this horrible modern life.
Do you think the type of nostalgia driving these trends can be harmful?
What's harmful is when you misunderstand the way evolution works and end up worried that because humans didn't use to do X, we shouldn't do X now. Almost all traits are a trade-off. Individuals with longer legs might survive better because they can run away from predators. But they might also get colder faster, because they lose more heat through their legs. The advantage or disadvantage depends on the environment you're in now.
Find out more in New Scientist’s gallery: "Paleo-trends: Separating fact from fantasy."
This article originally appeared in New Scientist.