New book counters the cave man craze

For a growing number of people, the good old days go back — way back — to the Paleolithic era.

Before civilization.

When people lived a life of hunting and gathering.

There are websites, blogs and dozens of new books (including the "Paleo Diet," "Paleo Solution" and, yes, even "Living Paleo for Dummies") that cater to Paleo-enthusiasts. These folks, who believe that humans reached their peak more than 10,000 years ago, often adopt some vestiges of Stone Age lifestyle by going barefoot or adopting the Cave Man Diet, which forbids such foods as grain and dairy.

The movement has found a foe in University of Minnesota biologist Marlene Zuk, author of a new book, "Paleofantasy: What Evolution Really Tells Us About Sex, Diet and How We Live." Zuk argues that Paleo-philes are making some unscientific assumptions, especially on how rapidly evolutionary changes can happen. We talked with Zuk at her office on the St. Paul campus about eating meat, exercise and the limits of instinct.

Q: Do you agree with the Paleo-enthusiasts that there's something unhealthy about our civilization?

A: Absolutely. There is something about modern life that is at odds with the way our bodies work. All you have to do is look around at the skyrocketing rates of diabetes. What I question is this assumption that we could turn back time and go back to some particular era and be better off.

A: There is no more reason to believe that one point of evolution is better or worse than any other. For example, eating meat is thought to have occurred originally through scavenging from animals already killed by lions or other predators, rather than through hunting.

So, when human beings moved away from scavenging and started hunting, should they have had this big angst of, "Oh, no! We evolved to be scavengers! Hunting is bad!"?

There is no end goal to evolution, so the idea that we had evolved to perfection and are now falling from grace is a misreading of how evolution really works.

Q: You seem to be questioning what is natural.

A: Yes. Some people say it's natural to eat a certain way or live a certain way. Does that mean that other forms that came before were not natural?

And of course, since all life arose in the sea, we could even argue that being aquatic is more natural than this newfangled thing of living on land and evolving lungs. Gills have worked very well for millions of years.

You see? Once you start dissecting the question of what is natural, it dissolves.

Q: What about instinct? Didn't humans act on pure instinct before we learned to think?

A: Instinct is also a very slippery concept. You can never say a behavior is instinctive, because all behavior is learned, at least to some extent. All behavior is a combination of input from the genes and input from the environment.

We always want to set ourselves aside, believing that humans are different from other animals because they operate on instinct and we have all of this culture. But in fact, culture affects our evolution.

A: The best evidence is the evolution of the gene that allows us to digest milk. After weaning, animals lose the enzyme required for breaking down milk sugar (lactose), so they have digestive difficulties (lactose intolerance). But some genetic variants allow us to consume milk.

We think people originally herded cattle for meat and hides, not for dairy. If a few people could drink milk after weaning, they'd have an advantage because they could use a food source other people couldn't. They'd be more likely to survive and pass on the genes to their offspring.

Ultimately, more people could consume dairy products, thus encouraging the cultural practice of herding cattle. And the cultural practice of herding makes the genes more prevalent.

Q: What does evolution tell us about how we should exercise?

A: If you compare our skeletons with chimpanzees or early human ancestors, it looks like we're adapted not just for walking but for running. For example, the way your skull sits on your neck and shoulders absorbs the shock during running.

Still, this doesn't lead to the conclusion that everybody should be running marathons.

Q: What do you think of the claim that sex crimes are caused by the evolutionary impulse to promote survival of the species?

A: Having sex is a big part of our makeup, but that's a really far cry from using a "my genes made me do it" defense. That just doesn't work biologically, legally or morally. We are not automatons.