Off the Shelf

Off the Shelf

Spring 2013
Craving Our Caveman Days
An interview with Paleofantasy author and evolutionary biologist
Marlene Zuk

By Deane Morrison
Photograph by Gary Bistram

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Sometimes it’s hard not to feel mismatched to modern life. Diet- and lifestyle-linked conditions like diabetes, hypertension, and obesity, which were unknown a few thousand years ago, are now common. But does this mean we’re adapted to a Stone Age diet and way of life and therefore should emulate our Paleolithic ancestors—an idea that keeps cropping up in the popular literature?

In her new book, Paleofantasy: What Evolution Really Tells Us about Sex, Diet, and How We Live, Professor Marlene Zuk, an evolutionary biologist at the University of Minnesota, argues that changing our diets and habits based on notions about an idealized prehistoric past is chasing a will-o’-the-wisp because human evolution is continual, bumpy, and fraught with trade-offs. Instead, we should understand how evolution works—particularly when it works fast, she says. Minnesota asked Zuk to explain more about this topic and her book, scheduled for publication in March.

Why did you write this book?
I think there’s a widespread misunderstanding of how evolution works and particularly about how fast it happens. What’s more, people often think evolution strives toward perfection of a species. I wanted to correct that notion.

What is meant by "paleofantasy"?
Paleofantasies are made-up notions about an idealized life before agriculture developed, more than 10,000 years ago, when humans were in some earlier stage of evolution. The fantasies involve small tribes with nuclear families where men hunted, women stayed with kids, and they only ate meat and plants that could be gathered. The idea is, the closer we can get to that state, the better off we’ll be because with civilization there’s a mismatch between the environment in which we evolved and one we live in.

"So early humans ate crackers. What’s the big deal?" Marlene Zuk writes in Paleofantasy (W.W. Norton & Co., 2013).

"The answer is that a reliance on starch in the diet calls into question the various forms of the so-called paleo diet. . . . If people are vociferous in their opinions about milk, they are positively fervent in their feelings about grains and other carbohydrates as suitable components of the diet. ‘Bread’ and ‘pasta’ seem to be fighting words for many of the proponents of a diet more like that of early humans." 

Did that state of ideal adaptation ever exist?
There was never a point where we were perfectly adapted to our environment. Evolution happens in fits and starts, and it’s chaotic, not directed.

What is evolution, anyway?
A change in gene frequency. For example, if blue-eyed people move into an area and have children with brown-eyed people, the frequency of the gene for blue eyes will increase in the population. But individuals themselves can’t evolve.

Are humans still evolving, and if so, how?
Yes, and it happens because not all people have the same number of children, so we see different representations of their genes in the genome. New techniques in genetics are letting scientists study the changes in the genome across populations and time to get a picture of what’s happening and why. We can see that certain genes evolved recently or rapidly in what’s called a "signature of selection" in the genome.

What about the argument that technology insulates humans from being weeded out by natural selection?
Technology can change selection. For example, people who earlier would have died from smallpox or myopia are alive now thanks to vaccines and eyewear. But we’ve also added selective pressures—for example, from new diseases like HIV/AIDS. Also, technology doesn’t operate the same all over the world. There’s still plenty of selection by disease, famine, infant mortality, etc.

What are some examples of rapid or recent human evolution?
The poster child for rapid evolution is the modern ability to digest lactose—milk sugar—using the enzyme lactase. In some humans, lactase persists after weaning. The trait appeared about 5,000 to 7,000 years ago in cattle-raising tribes, and in this short amount of evolutionary time it spread and became established in those populations. Promoters of "paleo diets" say that because earlier humans didn’t drink milk, and other animals can’t after weaning, then we shouldn’t. But I say, if you have the genes, do it. That’s not to say there’s anything wrong with paleo diets, just that following one solely because it emulates a particular version of our past isn’t based on good science.

In another example, it was recently found that Tibetans who live at high altitude show unique genetic traits that allow them to function on the Tibetan Plateau, which is thought to have been populated only 3,000 to 6,000 years ago. This underscores how fast evolution can occur.

Why can’t we evolve to an ideal point and then stop?
Evolution is a series of compromises and trade-offs. Genes have more than one function and interact in complicated ways. For example, the same gene that confers resistance to cholera if you have one copy may cause cystic fibrosis in double doses. And a gene that confers resistance to malaria if you have one copy causes sickle cell anemia if you have two. Also, consider a husky’s legs—longer is better for running but worse for conserving heat.

Is emulating an earlier state ever a good idea?
We can use contemporary hunter-gatherers as a jumping-off point, but you have to get data on what is beneficial. For example, a lot of people in the world run barefoot. If people using running shoes are getting injuries, and contemporary hunter-gatherers run barefoot, the best response is to study whether barefoot running really is better for runners elsewhere. There’s some evidence both pro and con, but only because people have studied the problem. 

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