Dysevolution: How changing habits are making humans sick

A new book proposes that cultural changes in the last few centuries have propogated non-infectious diseases that our ancestors didn't face

People walking.
Human evolution through the ages [Image Credit: Flickr : Gerardo Almaraz]

What do diabetes, nearsightedness and flat feet have in common?

They weren’t such a problem until a few hundred years ago, when cultural changes began to outpace human evolution.

While connecting evolution to myopia might seem like a stretch, Daniel Lieberman, an evolutionary biologist who teaches at Harvard, did just that, and convincingly too, at a recent talk at the American Museum of Natural History in New York. Studying evolution can actually answer a lot of questions you never thought you would ask, like why pregnant women don’t tip over, a study that won Lieberman a sarcastic Ig Nobel prize in 2009. A few years back Lieberman had gained worldwide recognition, when his research on the science of barefoot running was published as the cover story in Nature in 2010. In his recently published book “The Story of the Human Body: Evolution, Health and Disease,” Lieberman has tried to present the story of human evolution and answer a simple question — why is it relevant now?

“Natural selection is still going on today. Our Stone Age bodies are adjusting to being in the Space Age,” Lieberman says. “The difference is that now, an additional selection criterion of human culture is added.”

When seen through a macroscopic lens of the history of human life on earth, this truly is a good time to live. Numerous studies echo the same findings; the average lifespan is longer, infant mortality is down. Humans now have a better chance to live longer, healthier lives.

However, deaths due to non-infectious diseases such as cancer, heart diseases and diabetes are on a rise. Furthermore, people today also suffer from a higher incidence of lower back pain, dental cavities, myopia and mental health issues than ever before in the history of mankind. Almost all of these are examples of mismatched diseases, those that occur simply because our body has not evolved for modern times.

So, why are we seeing these mismatched diseases now? Lieberman suggests that “dysevolution,” a vicious circle of treating the symptoms instead of the causes of these diseases, is to blame. Like in case of diabetes, the genetic anomalies that could increase the  risk for developing it were always present in our DNA, however, changes such as increased consumption of processed foods and decreased physical activity have tipped the balance.

In the case of nearsightedness, changes such as an increase in reading habits or time spent indoors, have occurred slowly over the last few millennia and are thus hard to perceive, a characteristic of dysevolution. Most of all, these changes go unnoticed in the evolutionary scheme of things, since it has no effect on the reproductive success of an individual. Being myopic or diabetic hasn’t stopped people from having children.

Finally, the need for comfort has also spurred the rise of some mismatched diseases. Barefoot long-distance runners are less likely to suffer from flat feet than non-runners who spend their entire day in shoes. While shoes might make walking or running more comfortable, they have also made flat feet more common, with 30 percent of Americans suffering from it. And while orthotics don’t cure flat feet, they allow you to cope with the condition, thus contributing to cycle of dysevolution.

Put simply, humans have become quite lazy. Evolution drives humans to look for ways to reduce energy consumption in any activity, which means reduced physical activity and an increased vulnerability to problems that were not encountered a few centuries ago.

Although no one expects humans to stop adopting newer technologies, we could start adopting a healthier lifestyle. “Evolution still matters,” Lieberman says. “It is giving us clues or a path to how we can make the world a better place to live. How different would it be to encourage a child to indulge in increased physical activity, from making him use the seat belt or go to school?”

 

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