According to Daniel Lieberman, a professor of biological sciences at Harvard, an
important reason that we are sedentary is that humans have been selected by evolution
to exercise only as much as they must to survive. According to this theory,
a prominent adaptation has been for humans to develop prowess at running—for
example, humans have an Achilles tendon, an adaptation useful mainly for running,
and chimpanzees, our closest living relatives, do not. Running proficiency is a trait
essential for persistence hunting, still practiced in the Kalahari Desert, where small
bands of hunters chase animals until their prey collapse from overheating and exhaustion.
However, because during millions of years of evolution, the energy provided
by food was often scarce, human anatomy and physiology were also selected
to avoid unnecessary exertion and conserve energy for survival and reproduction.
“No hunter-gatherer goes out for a jog, just for the sake of it, I can tell you from
personal experience,” says Lieberman. In food-scarce environments, “They go out
to forage, they go out to work, but anything else would be unwise, not to mention

One report on Lieberman’s work commented that “humans were born to run— but
as little as possible.” Most human anatomical and physiological systems evolved
to require stimuli from physical activity to adjust functional capacity up or down in
response to the demands placed on them. Our bodies evolved to be adept at downregulation
of biological systems to slow metabolism and conserve energy whenever
possible. We did not evolve to stay healthy in an environment with plentiful food
and little need for physical activity. Because selection never operated to cope with
the long-term effects of chronic inactivity, mechanisms for conserving energy expenditure
now result in diseases. Without adequate stimuli from physical activity,
the result is poor health, including disuse atrophy of muscles, obesity, diabetes,
weakening of bones and osteoporosis, cardiovascular diseases, and even cognitive
decline and dementia.

According to Lieberman, there is no evolutionary-determined dose or type of physical
activity that will optimize health. “…because humans evolved to be active for
play or necessity, efforts to promote exercise will require altering environments
in ways that nudge or even compel people to be active and to make exercise fun.”
Lieberman thinks that one way to make exercise fun is to make it social. Other
steps to encouraging physical activity include having physical-education (PE) requirements
at schools and colleges and to making it easy in workplaces and communities.

When I was a freshman at Harvard, there was an exercise requirement,
but it was done away with in the 1970s, even though there is plentiful evidence that
physically active college students are happier and do better with their studies. The
bottom line is that as a society and as individuals, we need to fight back against two
million years of human evolution, telling us to take it easy when we can. Sloth
really is a deadly sin.

This blog presents opinions and ideas and is intended to provide helpful general information. I am not engaged in rendering advice or services to the individual reader. The ideas, procedures and suggestions in that are presented are not in any way a substitute for the advice and care of the reader’s own physician or other medical professional based on the reader’s own individual conditions, symptoms or concerns. If the reader needs personal medical, health, dietary, exercise or other assistance or advice the reader should consult a physician and/or other qualified health professionals. The author specifically disclaims all responsibility for any injury, damage or loss that the reader may incur as a direct or indirect consequence of following any directions or suggestions given in this blog or participating in any programs described in this blog or in the book, The Building Blocks of Health––How to Optimize Your Health with a Lifestyle Checklist (available in print or downloaded at Amazon, Apple, Barnes and Noble and elsewhere). Copyright 2021 by J. Joseph Speidel.