There’s an article in today’s New York Times about ways human cultures have influenced our own evolutionary biology. It’s an interesting piece. Much of the article focuses on diet.
There are some finer points on which the article does not touch, and some ideas in it with which I disagree.
This is something I’m only beginning to learn about; genetics and evolutionary biology are not my field. Even for those in these fields, it seems our understanding is fairly young when it comes to gene expression, gene-environment interaction, and the connections between diet, evolutionary biology, adaptation and environmental health.
There is a nuanced difference between ways we evolve because it’s advantageous, and ways we adapt our behaviors because we need to thrive in an environment or context faster than evolution can keep up. For example, the article talks about “the declining weight of the human skeleton that seems to have accompanied the switch to settled life, which started some 15,000 years ago.” It’s true; the archeological record shows that that agrarian life –– including the fairly rapid switch to a large-scale consumption of grains –– had two dramatic effects on the human skeleton: our stature shrunk, and our teeth got worse. Smaller bones were likely not a rapid evolutionary adaptation to farming, they were a consequence.
It seems we have adapted genetically more quickly to some components of dietary change than to others. Grains seem to be in the “others” group. Virtually every culture that traditionally consumes grains has historically treated them in ways that make them easier to digest, more likely to release their nutrients, and lower in compounds like lectins that interfere with our metabolic health. This happens through sourdough fermentation, soaking, sprouting, nixtamalization, rinsing, and probably other traditional techniques of whose effects we’re not yet aware. It’s faster to learn techniques like this than to evolve.
It also seems other aspects of diet — both inclusion of protective foods and avoidance of detrimental ones — moderate the effects of genetic susceptibility. Genetics is one of many factors at play when, say, a culture takes up and reacts poorly to modern ingrdients like white flour, vegetable oil, sugar, high fructose corn syrup, processed foods or factory-farmed meat (instead of grass-fed, although it’s still healthier than a meatless diet). Adding poor quality ingredients into a diet is, of course, often concurrent with losing healthier ones. Genetics is often highlighted when one ethnic group seems more susceptible to obesity or diabetes, but poor diet may simply be differently visible depending on genetic makeup. These foods aren’t good for anybody, both for the essential nutrients they lack and the detrimental components they contain, and it doesn’t look like we’re going to evolve to handle them anytime soon.
While the article doesn’t go into detail about the Masai (or Maasai) tribe of Africa, it does include a picture of Masai herding cows with the caption: “Maasai tribesman are among a culture with adult lactose tolerance.” The Masai traditionally subsist on three primary foods: meat, blood and milk. They’re extremely healthy. But one study (pdf full text) from 1979 found, surprisingly, unusually high rates of lactose intolerance among the Masai, although none of the symptoms I associate with lactose intolerance. Admittedly, this was a tiny study with many flaws: tiny sample size, no discussion of selection methods or confounders, to start. But it’s the only hit on PubMed under Masai or Maasai and lactose.
What if the Masai were lactose intolerant, by our biological definitions, but without any of the symptoms with which we associate lactose intolerance, like flatulence or digestive discomfort? What if the genetic variable that manifests as lactose intolerance when someone is living an unhealthy lifestyle, and eating unfermented and/or pasteurized dairy, manifests differently when they are eating a healthy diet?
Anecdotally, this makes sense to me. I had symptoms of lactose intolerance for years, and would probably still get pretty digestively upset if I drank a 16-ounce milkshake (although I’d get pretty unhappy if I drank 16 ounces of anything). But two things made my lactose intolerance all but disappear: I gave up gluten, and I eat primarily fermented and unpasteurized dairy, both of which are lower in lactose.
The gluten issue is key; some studies, like this one, suggest people with celiac disease who exhibit lactose intolerance symptoms lose those symptoms entirely on a gluten-free diet. I usually suggest to friends with lactose intolerance and unexplained digestive issues to try cutting out gluten for 2-4 weeks, and try raw and fermented milk products. It’s possible that some cultures which can’t seem to handle lactose could do so in other dietary contexts. A case of genetic and dietary confounding.
We’re certainly evolving as a species, and the way culture and diet and socio-environmental factors affect that will be a subject of exploration and interest for a long time. But we have to remember it works two ways: we evolve to respond to culture, we create culture that reflects both our evolutionary adaptations and limitations.
Sources of local raw dairy
The following Washington State farms sell grass-fed raw milk at various farmers’ markets, co-ops or “natural foods” stores:
Dungeness Valley Creamery
Sea Breeze Farms
St John’s Creamery (goat milk)
Thanks to striatic for the flickr CC photo.