Evan Hazard: Genetics and diet: A scientific controversy
In November of 2010 and January of 2011, we discussed primary and secondary biological literature. Actually, you have read sterling examples of secondary lit in this newspaper, by microbiologist Patrick Guilfoile, now associate academic vice president at Bemidji State University. His columns usually review recent findings in biology, oftentimes our biology in relation to other critters, mostly microscopic ones. They are not reports of his original research, and therefore are secondary lit, but they cite primary reports of recent work, often from two top-flight weeklies, “Science” and “Nature.” Patrick excels at making science accessible to laypeople.
I used to get “Science,” but it’s a weekly and I couldn’t keep up. The only primary journal I get now is the “Journal of Mammalogy.” But I read secondary periodicals, such as “American Scientist,” “Natural History” and “Scientific American.” I also encounter decent science writing in lay magazines, including “Mpls St Paul,” “The New Yorker” and “Minnesota Monthly.” “Harper’s” and “Atlantic Monthly” also contain credible science writing, but I rarely see them.“The Caveman Controversy” in August’s “Minnesota Monthly” starts with a striking two-page drawing of a well-toned woman raising a massive drumstick as a weapon. Initially, I thought she was a cavewoman, but she’s in a black sports bra and gym shorts. No, she’s an enraged advocate of the “Paleo Diet” thrashing books entitled “Paleofantasy” by University of Minnesota entomology professor Dr. Marlene Zuk.Dr. Loren Cordain founded the paleo diet movement, and has done several paleo diet books and DVDs. He has a bachelor’s degree in health sciences and a master’s degree in science and a doctorate in exercise physiology. His central claim is that our dietary genetics is largely the product of millennia of adaptation to the diet typical of hunter gatherer societies during Paleolithic (Old Stone Age) times. Many hunter-gatherer groups today eat mostly meat, supplemented with plants of various sorts, but with no cultivated grains or milk from dairy animals. Cordain connects various modern ailments to our failing to maintain a paleo diet. He has many converts who swear by it.Zuk, author of “Paleofantasy,” has bachelor’s and master’s degrees in biology and a doctorate in zoology. Her previous books’ topics include the sex life of insects, what we can and cannot learn about sex from other animals, and the role of disease and various parasites in human evolution. Those topics don’t sound like things that would disturb Cordain. On the other hand, the title “Paleofantasy,” subtitled “What Evolution Really Tells Us about Sex, Diet, and How We Live” obviously challenges Cordain’s claims.Zuk’s book mentions diet only incidentally. Her major objection to Cordain’s thesis is that he does not have his genetics right in two respects. One, he claims our food-related genetics have changed little, since not been enough time has elapsed since the Paleolithic ended about 10,000 years ago. Two, he seems to think this is a species-wide hereditary pattern.Zuk faults him on both counts. There has been plenty of time since for adaptive genetic change in human populations. One example, which she cites, is the spread of lactase production’s persistence into adulthood in populations that began to ingest milk from cattle, goats, sheep, camels, and horses. Most human groups, like most other species of mammals, lose their ability to digest lactose sometime during childhood, but adult persistence of the lactose-digesting enzyme lactase is common in originally European sorts like many of us, cattle-raising blacks in East Africa, Mongols and others.Second, early human populations vary now and probably varied then, eating various diets in various Old World (and later New World) regions, and there is also great genetic variation both within and between human populations. Natural selection can easily spread a favorable mutation throughout a population in several generations.You, of course, recall this from my columns in June 2007 and July 2008 about the evolution of six or seven new species of leaf roller moths in Hawaii in perhaps only a few hundred years after Polynesians first settled there. Zuk uses her own observations of the evolution of silent male crickets in only decades. See http://evolution.berkeley.edu/evolibrary/news/061201_quietcrickets>.Recently, I answered a legitimate telephone survey. At the end, the caller asked if I was in my 50s, 60s or 70s. She was surprised when I said I’m 83 — I didn’t sound that old. I told her I work out three times a week and drink a quart of milk a day. That’s not the whole story, of course. I also limit my fat intake and eat other things, many of them inconsistent with the paleo diet. It may be fine for some people, but its theoretical genetic basis is shaky. Its emphasis on meat, of course, puts it out of reach of most of Earth’s 7 billion people. EVAN HAZARD, a retired BSU biology professor, also writes “Northland Stargazing” the fourth Friday of each month.