exercise, a new evolutionary model

A recent article in the Scientific American suggested a different conceptual model of exercise, based on evolutionary anthropology (see Pontzer H. Evolved to Exercise. Sci Am. January 2019, 23-29). Appropriately perhaps, I read this article while working out at the gym….

Basic points:

-- though we share more than 97% of our DNA with orangutans, gorillas, chimpanzees, and bonobos, there is a fundamentally different necessity for exercise with us. Homonins split from chimpanzees and bonobos in the primate family tree around 7 million years ago

-- Chimpanzees, for example, wake up early, then eat fruits, then nap, then some grooming, then eat again, then another nap, then dinner, and then go to sleep. Similarly for orangutans, gorillas and, and bonobos. They spend 8 to 10 hours a day resting, grooming, and eating, then 8 to 10 hours of sleep at night

-- in terms of exercise, chimpanzees walk about 3 km a day, gorillas and orangutans less. Chimps climb about 100 meters a day (equivalent to another 1.5 km of walking), orangutans are similar, gorillas less. This is much less than the recommended exercise for humans, and would be expected to lead to significant increased risk of disease as well as shorter lifespans.

    -- A study of Scottish adults found those watching more than 2 hours of television day had a 125% increase in cardiac events.

    -- A study of Australian adults found that every hour watching TV shortened life expectancy by 22 minutes.

-- And chimpanzees have very high cholesterol levels.

    -- chimps in captivity have higher total cholesterol and LDL levels than humans (total cholesterol in the 200 to 250 mg/dL range, LDL in the 170 range (see https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3352420/ )

    -- and, chimps and all of the great apes are homozygous forAPOE4 alleles, a significant human cardiovascular risk factor

-- yet, even in captivity, they have less than 10% total body fat, blood pressure does not increase with age, and atherosclerosis and diabetes are extremely rare in these animals (!!!)

-- The author argues that the evolution of an upright, striding bipedal gait coupled with developing stone tools was associated with increased meat eating, since humans were able to cover much more ground and be more efficient at hunting

    -- species tend to evolve based on the foods that are available. One example is that early mammals could make their own vitamin C, but as our primary ancestors tens of millions of years ago began to eat fruits rich in vitamin C, mutations developed so that we can no longer make vitamin C

    -- carnivores, and those with particular fruit-eating diets for example, tend to travel much more to feed themselves

    -- also, relying on meat as a food requires more cooperation and sharing

    -- hunting also requires a higher level of intelligence, with steady increases in brain size and technological complexity

-- not surprisingly, hunter-gatherers are very active, typically covering 9 to 14 km a day on foot (about 12,000-18,000 steps)

-- the Hadza hunter-gatherers in northern Tanzania, for example, have more  physical activity a day than Americans get in a week, and they travel 3 to 5 times father every day than any of the great apes

-- The point here is that humans have evolved as exercising animals

    -- there even is an inherent reward system for exercise, the production of endocannabinoids and endorphins (the “runner’s high”)

    -- exercise leads to the release of neurotrophic molecules that promote neurogenesis and brain growth, and also improves memory, may decrease cognitive decline and helps mental health/happiness http://gmodestmedblogs.blogspot.com/2018/09/exercise-helps-mental-health.html; http://gmodestmedblogs.blogspot.com/2013/08/exercise-and-memory.html  

    -- as compared to chimpanzees, our maximum VO₂ is 4 times higher than chimpanzees (largely from changes in our larger leg muscles and greater proportion of slow-twitch muscle fibers; also more blood cells to carry oxygen; higher metabolism)

-- exercise has a myriad of positive effects, though, unfortunately, weight loss is not clearly one of its benefits (Hadza hunter-gatherers burn basically the same number of calories as sedentary Westerners)

-- but, exercise does reduce chronic inflammation, lowers testosterone/estrogen/progesterone levels (which may decrease risk of reproductive cancers), decreases the early AM cortisol rise, increases insulin sensitivity, increases lipoprotein lipase activity in the blood (leading to increased muscle uptake of circulating triglycerides), etc.

    -- And, several of these effects likely decrease the risk of immunologic problems (especially given the immunosuppressant role of cortisol, which is decreased with exercise)

    -- the Hazda, who walk more than 2 hours a day, do not have heart disease, diabetes, and many of the chronic diseases of Western society

    -- a study of Glaswegian postal workers found that those who got 15,000 steps a day have much less heart disease than those who sat while at work, and much lower levels of metabolic syndrome (see https://www.ncbi.nlm.nih.gov/pubmed/28138134 , as well ashttps://www.nytimes.com/2017/03/22/well/move/should-15000-steps-a-day-be-our-new-exercise-target.html

--of course, there are limitations to the scientific rigor of this exercise thesis. There are certainly holes in the data on great apes’ lifestyles, beyond the observations of what they eat and what they do for exercise. And, the comparison between the Hadza and we Westerners is also more complex than looking at their exercise and lack of atherosclerosis.

--but, this evolutionary model of the human need for exercise does seem plausible on the surface.  Because of needs for food, dictated presumably by environmental/food source changes, humans evolved slowly to being largely hunter-gatherers. Hand-in-hand with this, they developed more mental capacity to create tools to hunt more efficiently as hunters, as well as the ability to run very large distances (the advantage of the slow-twitch muscles) to catch the roaming food. Now, with the further development of the brain, we have invented other more modern technologies to hunt and gather the meat. But, now we have the burden of lack of need for exercise, which seems to have many adverse health and longevity effects, as a result of not fulfilling our prior evolutionary imperative. So, perhaps we need to wait a few eons to evolve further (though, of course, the complicating factor is that these chronic diseases we have now developed tend to inflict their harms in the post-reproductive stages to life, which do not really influence evolution). In this light, there was a really interesting book on a Mexican group, living in remote mountains, who were remarkable runners: (see Christopher McDougall's  “Born to Run: A Hidden Tribe, Superathletes, and the Greatest Race the World Has Never Seen”)

so, interesting article. i had thought that these nonhuman primates were exceptionally physically active (but instead are lazy slouches) and very physically fit (which they do seem to be). and Pontzer's thesis that we have evolved to require exercise seems pretty plausible. so, the clinical challenge, both from the perspective of this conceptual framework and from many many many observational studies on exercise, is how to integrate exercise much more into all of our lives, when the technological advances are driving us (so to speak) in the other direction.....

for the many prior posts on exercise, see:

http://gmodestmedblogs.blogspot.com/search/label/exercise 

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as another relevant article, a recent meta-analysis/systematic review of 10 studies found that the number of steps/day was inversely related to arterial stiffness, an independent predictor of cardiovascular morbidity or mortality (see exercise arterial stiffness hypertension2018 in dropbox, or DOI: 10.1161/ HYPERTENSIONAHA.118.11987)

geoff

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