Why Humans Evolved to be Active

Humans of all to be much more physically active than our ape ancestors. Typical chimpanzee walks maybe two to three kilometers a day, and they take maybe what, three, 4,000 steps a day. A typical hunter-gatherer takes about 15 to 20,000 steps a day. Per kilo hunter-gatherers spend about twice as much energy per kilo on being physically active per day than our ape cousins. And importantly, that physical activity occurs as we age, right?

So Americans are pretty inactive, as we all know. A typical American in twenties might be, you know, get spend 30, 40 minutes a day being physically active. And by the time most Americans hit the age of 70, they may be doing 10 to 20 minutes a day of moderate to vigorous physical activity. Hunter gatherers in Tanzania are way more active in their twenties and thirties. They're doing three, four hours a day of physical activity. And although that declines by the time they're 70 or 80, they're still doing two to three hours of physical activity a day. That's well more than 10 times more physical activity per day than a typical American.

So we evolved to stay active as we age, and the reason for that is that activity is to do stuff. It's not like we don't retire, we don't go to the beach, we don't go to Florida. Hunter gatherers continue to gather, they continue to hunt, they continue to take care of children, and they produce an energetic surplus which they supply to their children and their grandchildren. And that surplus can amount to somewhere between 250 to whopping of 3000 calories per day. That's substantial. So yes, human beings were selected to be moderately physically active and to stay active as we age, including after we stop reproducing.

Now, the second part of the active grandparent hypothesis is that there was selection from moderate physical activity to slow aging and decrease vulnerability to disease, thereby extending health spans, and as we talked about before, also lifespans. And if you want proof of this, one of the best studies ever done was the Harvard Alumni Study done right here in my university, Harvard University, by Ralph Paffenbarger, and Paffenbarger studied over 20,000 Harvard alumni. And he looked at them from all ages. And by the way, when you do that, you're basically correcting for socioeconomic status. And what he showed was that alumni below the age of 50 who were getting about 2000 calories a week of exercise, had 21% lower death rates than alumni who were inactive. And that's after correcting for smoking and various other sorts of things like that. By the time they got to their fifties, the more physically active alumni had 36% lower death rates. And in their seventies and their eighties, those exercising alumni had 50% lower death rates than sedentary alumni of the same age. That's a amazingly large effect, right? And what he's showing here is that as we get older, exercise not only helps you get, you know, stay healthy, it becomes more important as we get older.