Our ancestors were much stronger than we are — here’s how to rebuild those abilities

But we do know that thousands of years ago, those ancestors spread out across the globe, crossing deserts like the Sahara and freezing regions like Siberia, scaling mountain ranges including the Alps and Himalayas, and even crossing segments of the ocean to populate new lands.

When you look at the physical feats those people accomplished, they put us all to shame.

But the ability to accomplish all of that wasn't due to some kind of human superpower that's been genetically lost, as Scott Carney, author of "What Doesn't Kill Us: How Freezing Water, Extreme Altitude, and Environmental Conditioning Will Renew Our Lost Evolutionary Strength," recently explained at a TEDx talk at the University of Colorado in Boulder. Those abilities are what he calls "human powers" — and we can still learn to resist cold, survive extreme heat, and last on long journeys at high altitudes.

"Our species, Homo sapiens sapiens, has walked the earth for about 200,000 years, in that time, we endured crippling cold and scorching heat; we trekked out of the Middle East over the Alps, over the Himalayas, we even populated the New World without a whisper of what any one of us would consider modern technology," says Carney. "Our most valuable asset in all of this has been our body — it doesn't matter whether it's a snowstorm or a scorching sun, our bodies had to adapt quickly if we wanted to survive."

A third pillar of fitness

Carney believes that rebuilding those abilities to resist extreme conditions will do more than just let us enjoy a swim in an icy lake — he thinks there's good evidence that doing so can transform our health.

The argument is that our bodies adapted to have mechanisms that help us respond to extreme temperatures and other environmental conditions. Without engaging the parts of our circulatory systems that help us cope with extreme heat and cold, Carney says, we weaken those mechanisms. And that weakness could potentially play a role in cardiovascular illness.

Someone with a seemingly "perfect" body might still be hiding weak circulatory muscles, Carney says in his talk. And there is good evidence that our bodies are ready to adapt to extremes if we just put them in those circumstances.

"There's an entire hidden biology honed to deal with various environmental conditions," says Carney. "Extreme heat will let your pores encourage evaporation; if you go into the cold, you will ramp up your metabolism; if you go into altitude, you will get more red blood cells in order to compensate for the decreased oxygen."

Medical research affirms at least some of this. Studies have found that a combination of cold exposure and learned breathing techniques can help people gain a limited amount of control over their immune system, which was previously thought to be completely involuntary. Promising data also suggests that cold exposure could help people lose weight and could counteract some effects of type 2 diabetes.

Others have argued that emulating our paleolithic ancestors could help us regain some sort of lost fitness in other ways. That's the idea behind the various versions of a paleo diet, though what such a diet should be comprised of is more complicated than many adherents would have you think.

When it comes to pure physical fitness, "Born to Run" author Christopher McDougall — who previously popularized a a back-to-human-basics style of endurance running — most recently put forth some pretty strong arguments in favor of workouts like climbing and parkour that emphasize natural movements in his latest book, "Natural Born Heroes."

In a way, this fits with what Carney is asking people to try: challenging themselves with the sort of obstacles and environments that we find in nature.

He asks in the TEDx talk, "What was it about our ancestors that was so much stronger?"

His answer: "The difference between your paleolithic grandfather and grandmother and us is that we have the ability to manipulate the world around us with technology." But perhaps relying too much on that technology makes us weak.