In the book “Born To Run,” Christopher McDougall provides a lot of scientific evidence that supports the idea that humans may have evolved to be fantastic runners.

In a scientific paper in the journal of Sports Medicine, Daniel Lieberman, a Harvard evolutionary biologist, and Dennis Bramble, a biologist at the University of Utah, wrote that as the human body changed over time, it adopted key characteristics of a running animal.

Here are some of those key adaptations humans evolved to have:

1) Humans have toes that are short and straight, rather than long and splayed out. These kinds of toes allowed for more efficient running, compared with longer toed animals. Increasing toe length as little as 20 percent doubles the mechanical work of the foot.

2) Humans have big butts, which is the largest muscle in the body. Big butts are also only necessary for running. You can test this yourself: clutch your butt and walk around the room. It’ll stay soft, and only tighten up when you start to run. Your butt’s job is to prevent the momentum of your upper body from flipping you onto your face.

3) Humans have millions of sweat glands, which is the best system for cooling. Because we cool by sweating rather than panting, we can stay cool at speeds and distances that would overheat other animals. As long as we keep sweating, we can keep running.

4) Humans have spring like ligaments and tendons in our feet and legs, which is crucial for running.

5) Humans have a far more developed sense of balance than other animals. Humans have a narrow waist and a midsection that can turn. This allows us to swing our arms and prevents us from zigzagging while we run.

6) Humans have a nuchal ligament, which is the little known tendon behind the head. The nuchal ligament is useful only for stabilizing the head when an animal is moving fast. This is why walking animals like chimps and pigs don’t have one, while running animals like dogs and horses do.

But this raises a few questions.

First, if we were born to run, why are we so incredibly slow at it? I mean, compared to a squirrel, Usain Bolt doesn’t stand a chance.

Well when it comes to running, there are two kinds of great runners: There are sprinters and there are marathoners. And according to McDougall, humans have evolved to be great marathoners.

Second, if we were born with the body to run marathons, then why aren’t there more people running marathons?

Unfortunately, this is because humans have a mind-body conflict. We have a body built for performance, but a brain that’s always looking for efficiency.

In “Born To Run,” McDougall says,

“We live or die by our endurance, but remember: endurance is all about conserving energy, and that’s the brains department. The reason some people use their genetic gift for running and others don’t is because the brain is a bargain shopper. The brain is always scheming to reduce costs, to get more for less, to store energy and to have it ready for an emergency.”

This makes sense. Throughout our entire evolutionary history, sitting around was a luxury, which meant that when hunter gatherers had the chance to rest, they took it. Only recently, however, have we come up with the technology to turn lazing around into a way of life.

We’ve taken our strong, durable, hunter-gatherer bodies and dropped them into a world of leisure.

By doing this, though, we’ve taken away the jobs our bodies were meant to do. As a result, we’re now paying for it. Nearly every top killer in the western world, such as heart disease, stroke, diabetes, depression, hypertension, and a dozen forms of cancer, were all unknown to our ancestors.

If you’re like me and you love to run, then you know how good running can feel because we’ve made a habit of it. But lose the habit, and your ancient survival instincts will be urging you to stay in bed and relax.

This is the bitter irony: People are built to run marathons, but they’re also built to be lazy.