Forty or fifty years ago, psychologists and other scientists talked about “genes” determining this or that. ( James Watson still talks this way.) A certain percentage of the variation of this or that (e.g., intelligence) was attributed to “genes”. Hardly anyone outside genetics or behavior genetics knew what this meant, but many people thought they did. In reaction to the huge misunderstanding (e.g., those who said intelligence was “80% genetic” but did not know what this meant), psychologists began to talk about gene-environment interaction. “Is the area of a rectangle determined by its height or its width?” they like to say.
But notice how fact-free this view is. A tiny number of studies have observed gene-environment interactions but they are very difficult. I think this has made it hard to realize something basic and important. Years ago, I heard a talk about squirrel circadian rhythms by Patricia DeCoursey, the scientist who introduced the concept of phase-response curves. At her talk, she showed results from about 15 squirrels. She tested each one — with an emphasis on individual results that resembles self-experimentation — to determine how much light it needed to become entrained to a 24-hour light/dark cycle. One squirrel needed much stronger light than the others.
Here was an interesting finding that another scientist might have missed. What did it mean? Because the squirrels lived under very similar conditions (e.g., identical diets), it was almost surely a genetic difference. Let’s assume it was. In nature, sunlight is plenty strong. The lab light was weaker. In nature, the genetic difference wouldn’t make an observable difference. Only under artificial conditions did it become visible. It only became visible when the artificial conditions didn’t supply enough of something important (sunlight). In other words, the newly-visible genetic difference implied there was something lacking in the artificial conditions. The genetic difference implied the environment mattered. The opposite of the usual interpretation.
I don’t know any reason to think this is an unusual case. Aaron Blaisdell told me a story that shows its relevance to human health. Aaron is unusually sensitive to sunlight. Until recently, he could only spend 5 or 10 minutes in the sun before it became unpleasant. The condition is genetic. His mother has it; her father had it. It’s called Erythropoietic Protoporphyria. It is autosomal-dominant. Scientists even know where the gene is. That’s where the understanding of most scientists stops. A genetic condition. Recently, however, Aaron drastically changed his diet with great results, as noted earlier. At the same time as the dietary changes, his sun sensitivity got much better. He can now stay in the sun for an hour or more without discomfort. This is a gene-environment interaction, of course, but of a particular sort: The genetic effect showed there was something wrong with the environment, just as it did in DeCoursey’s experiment.
Sure, there’s always genetic variation — it’s just usually hard to see. The wrong environment makes it much easier to see. It reveals a range of genotypes, all of which would be harmless in the right environment. So when you come across a “genetic disorder” such as Erythropoetic Protoporphyria, it is likely to imply an environmental problem. No one had ever told Aaron or his mother or her father that their condition suggested that environmental changes would help them.