One night last week I was on my evening dog walk crunching along in the crisp, 10 degree, Minnesota snow. I sat down on a bench in a wooded area by a creek and stared at the dark sky, the stars, and the bright white full moon that casted long shadows among the trees. I wrapped myself up in the magnificent blanket of silence that surrounded me and watched the clouds of my breath puff out into the cold.

The silence and darkness of my dog walks are the keys that unlock my attention from the actions of life. It’s the critical pause in my day that gives my mind the freedom to sniff out random thoughts and to follow their trail without distraction or judgment. Sometimes the trail leads nowhere, other times to real gems.

That night my German Shepherd Joker plopped down on his side on top of crispy frozen snow, and just laid there, and stared at me, totally comfortable, and happy. He could have laid there all night and had a good nights sleep. Me, I was sitting on the bench with long underwear, jeans, thick socks, Sorel winter boots, t-shirt, sweater, hoodie, stocking hat, and a massive down jacket that, to use the tired cliche, makes me look like a Michelin Man.

I hit the mental trail and started to sniff around about how vulnerable I was without all those clothes. Next I imagined being down by the creek clad only in my lulu lemon underwear handcuffed to the bench. I wouldn’t last even two hours. Obviously this is because I ain’t got any fur, like my dog Joker. I kept sniffing. Why is it that we are all so bald, since being bald makes us so vulnerable to the outdoor elements?

Most of us only have any serious amount of hair on our heads, under our arms, and in our lulu lemon underwear.

I called my daughter Maya from the bench and asked her if she had ever wondered about this. She hadn’t, and she indicated that she was in the middle of something and that she would call me back later.

I hung this curiosity in my mental closet until I got home and logged onto pubmed to do a literature search. It wasn’t easy trying to figure out the keywords to search, but the trail took me to a paper, Run For Your Life, by Timothy Noakes and Michael Spedding in the uber prestigious journal Nature, that explained the dilemma.

Turns out we are bald so we can walk and run, for a long time, unlike my dog Joker. After just a 3 mile run is he tapped out, lying on his side, panting a million breaths a minute, with his long pink tongue draped onto the dirty floor, all because he can only get rid of heat by panting.

Having no hair means we humans can sweat, a lot. Up to 3 liters an hour. Which means that, unlike Joker, we can get rid of heat, and fast.

My daughter Maya ran the Twin Cities Marathon last October. Nearly 10,000 people ran it, and as I watched the throngs of runners that clearly didn’t look like “elite athletic gods” plod by, I realized that almost anyone can run a marathon, if they work at it.

This whole no hair thing started millions of years ago when climate shifts changed the forests of Africa to a more open savannah. Now our brothers and sisters, the apes, who hung out most of the day in trees, had to deal with trying to hunt and kill their dinner out in the open. They adapted by evolving a skeleton and the exercise capacity that allowed them to walk and run, for hours, so they could chase down their prey.

Not so with other primates and most animals. All that hair or thick skin means they can’t sweat like us, so they can’t get rid of heat, so they can’t run long distances. When they try they overheat, collapse on the ground, and just lay there and pant, like my dog Joker.

But there was another problem. Imagine that you are one of those early hunter gatherers. The only weapon you have is a big stick or a stone. There is no way you are going to go out on your own and try chase down some animal that could run faster than you and who has a set of choppers that can rip your arm off in one bite. You needed help, and lots of it, to capture and kill your next meal.

So, as we evolved to be able to walk and run long distances, we also evolved the ability to cooperate, with each other, to survive. As our skeletons and muscles changed, our brains grew bigger as we developed the ability to plan, coordinate, track, and communicate with each other as a prey killing team.

Working as a team we could chase an animal down until they overheated and collapsed, and then beat them to death with our big sticks and stones as they lay there panting. Then it was dinner time after a great day of running and teamwork.

Our survival as a species depended on our ability to run and our ability to be connected to each other. Our muscles and brains grew up in the human household as siamese twins. When we exercise, a flood of molecules called myokines are released into the blood that act directly on the brain to improve memory and increase neuroplasticity. Our minds are literally connected to the use of our muscles.

Exercise and human connection are baked into our genes as part of our human operating system. It is why being sedentary and lonely are two of the biggest killers of our species.

It was a matter of survival then, and it’s a matter of survival now.