How human evolution causes diseases
John DiTraglia MD
I just read a book, recently featured on the Cobert Report, by Daniel Lieberman, professor of human evolutionary biology at Harvard, called The Story of the Human Body (1) that’s about how our genes, programmed during evolution, cause lots of disease, the most prominent of which is obesity.
The first half of the book talks about chimpanzees and Australopithici and early human species and is full of interesting nuggets like:
- Page 85, “it costs the same number of calories to run five miles at a pace of either seven or 10 minutes per mile.” This is hard to believe because I know it’s much harder for me to do fast than slow.
- Page 91, “brains and guts each consume about 15 percent of the body’s basal metabolic cost… our brains and gastrointestinal tracts (when empty) are similarly large, weighing slightly more than 1 kg each. In most mammals of the same body mass, the brain is about a fifth of the size of a human’s, while the guts are twice as large…Homo essentially traded off large guts for large brains by switching to higher-quality diets.” (On Page 109 he says, “..brain costs 20-25 percent of resting energy” and on Page 117, “an adult’s brain consumes ..20-30 percent of the body’s energy budget.” I guess those are estimates from different primary sources.)
- Page 112, “It takes a whopping 12 million calories to grow a human into an 18-year-old adult, roughly twice as many calories as it takes to grow an adult chimpanzee.”
- Page 116, “Short interruptions or deficits of blood sugar [to the brain] that last more than 1-2 minutes cause irreparable, often lethal damage…How did early human mothers (and their children) survive such shortages…[… from famine or illness]? The answer is lots of fat… humans are unusually fat compared to most animals.” Humans use it to keep their brains alive. Seals and penguins who are some of the animals that might have more fat than humans use it for insulation.
- Page 120, “…cutting, grinding and pounding significantly lowers the cost of digesting both plant and animal foods…potatoes yield roughly twice as many calories or other nutrients if you eat them cooked…Another benefit of cooking is that it kills germs…”
But then on page 160 Professor Lieberman says that he has been teaching human evolution to college students for more than 20 years and for most of that time he wound up his story of human evolution at about the end of the Paleolithic era before farming, about 10,000 years ago when human evolution mostly, but not entirely, stopped. He says that, “I now regret the way I used to teach human evolution.” So here he starts the main point of this book - that human evolution has ill-equipped us for living the way we have for the last 10,000 years and causes “mismatch” diseases and maybe even “dysevolution” that might make us evolve in the wrong direction. This is the new vogue point of view that because we spent maybe 2 million years being hunter-gatherers we are poorly equipped to be farmers, much less city dwellers. But this part of the book is much less interesting and less satisfying. It is repetitious and gives the standard Paleolithic diet and sugar/insulin are the enemy stuff. He makes the same kind of logical error that obesity books make when he says things like “[we should]… focus more intelligently and rationally on the causes rather than the symptoms of these diseases…being overweight or obese are not diseases.” (Page 291) If we can manage to not CAUSE obesity then it IS somebody’s fault when a person is obese.
Some non-obesity evolutionary mismatches include:
- Elevated estrogen levels increase the incidence of breast and uterine and ovarian cancer. Estrogen is made by fat cells in addition to what the ovaries make, and estrogen decreases with exercise. Also living longer and not having babies increases exposure to estrogen.
- Hunter gatherer - Paleolithic skulls don’t have impacted wisdom teeth or cavities. Pre-industrial farmer skulls have lots of cavities and abscesses but less than 5 percent have impacted wisdom teeth. But skulls from the last 100 years have both because we don’t chew enough. Maybe we should chew more gum.
- Shoes cause heel strike walking that leads to knee problems and fallen arches and plantar fasciitis. We should walk bare foot more often.
Myopia comes from reading too much. I have probably spoiled this book for you but I may have helped prevent your myopia.
1. 2013 by Pantheon Books/Random House, New York.
Local Gas Prices