This article is not for everyone… before you read it, take this simple two question survey to make sure it’s right for you:

1) Do you like ice cream?

2) Do you like sex?

If you answered yes to both questions… I suggest you keep reading.

I promise, we’ll circle back to sex and ice cream shortly… but before we do, I’d like to share a childhood memory.

I grew up in San Diego, California, home of the world famous San Diego Zoo. One morning before school, a photo on the front page of our local newspaper caught my attention. The picture was of a polar bear, lying on his belly, draped over a block of plastic “ice” in the outdoor enclosure at our famous hometown zoo. The accompanying article said that he was depressed, and that zookeepers we’re going to start him on Prozac.

I was just a kid (with no veterinary training) but I was pretty sure I knew why the bear was sad. Polar bears are optimized for cold. They are big, fat, furry, and white for a reason: they are adapted for frigid Arctic temperatures. When a polar bear winds up in sunny San Diego… things are going to turn out badly, and depression is just the beginning.

The depressed polar bear is a classic example of a “mismatch disease,” in which an illness or symptom is the result of a body that is not optimized for the environment in which it lives. Polar bears are built for freezing cold — is it any wonder he would be depressed in hot dry weather? That bear didn’t need Prozac, he needed his home, or at least conditions more like it. (Note: I am happy to report that the polar bear enclosure at the San Diego Zoo has significantly improved since those days, although they’d still be better off somewhere colder.)

In much the same way as polar bears have adaptations that allow them to thrive in cold weather, humans function best in conditions where there is very little food and lots of activity. When a human saddles up in front of a massive Sunday brunch buffet and then sits on the couch the rest of the day… there’s going to be a problem. Our bodies were simply not made for that.

It may not always feel like it, but your body is a finely tuned machine that is optimized for peak performance on this planet. At least it used to be. Let me explain…

The genes that we carry today were passed down from our ancestors, honed and refined for “survival of the fittest.” Natural selection is a fairly simple principle: individuals that are better adapted to their surroundings are more successful at reproduction.That’s why we like sex. It’s all about survival. Individuals that are more “fit” are more successful, and therefore get the advantage of passing their genes along to the next generation. That’s how the generational cycle continues. During the vast majority of human history, changes to our surroundings have happened very slowly and have generally given species (including humans) plenty time to adapt.

Every day, our distant ancestors woke up wondering if they would be lucky enough to eat that day. Individuals who had a stronger craving for calories (especially fat and sugar) we’re more likely to survive. And that is exactly why you like ice cream. It’s programmed in your genes because, again, it’s all about survival.

Today, food and calories are plentiful. In fact, there’s more food available to most of us than we could possibly ever eat. Our ancestors would marvel at how much there is to eat, and how little effort is required to get that food. The word we live in now would be unrecognizable to them in other ways, too. We’ve automated tasks so that we don’t have to do as much physical work. Cars and buses take us where we need to go so we don’t have to walk or run. We sit for hours every day. We wear shoes. All of theses are luxuries that our distant ancestors never could’ve imagined. In their world, food was scarce, and constant physical activity was required. Our world is quite the opposite.

In the last several hundred years, humans have made remarkable advances in technology that have led to a major acceleration of changes to our environment, our surroundings, our culture, our lifestyle, and our diets. As a result of these shifts, we are now living in a world that our bodies are no longer well suited for. It’s a mismatch… and it sets the stage for a whole host of illness and disease.

Daniel Lieberman is a human evolutionary biologist at Harvard University who is blazing the trail when it comes to the study of mismatch diseases. In his fascinating book, The Story of the Human Body, Dr. Lieberman discusses many common examples of modern-day mismatch diseases including: allergies, anxiety, back pain, depression, obesity, heart disease, hypertension, tooth decay, type 2 diabetes, and many deadly cancers.

When we look closely at the diet and lifestyle of the modern day human, it’s not surprising that we are facing an epidemic of mismatch diseases. We are polar bears in San Diego. Our bodies aren’t built for this. We’re living with hunter/gatherer genes in a fast food nation. If we don’t recognize it and make a change, chronic illness and untimely death is a virtual certainty.

Thankfully, it’s not all bad news. There is a solution to keeping mismatch diseases at bay. It’s a simple formula that involves eating, moving, and behaving more like our hunter/gatherer ancestors. It starts with eating a whole plant based diet and eliminating processed junk food. It means you step up your physical activity starting with a daily walk of at least 20 minutes.

The goal here is not to go back to life as cave-people. We do not need to live primitively to avoid mismatch diseases. Understanding the factors that underlie these illnesses allows us to “have our cake, and eat it too.” We can absolutely embrace technology and the conveniences of modern-day life and use them to help us thrive. It’s up to you…

– Dr. Joshua Levitt