In today's NYTimes, David Brooks has a thoughtful, intelligent column about how mainstream science is gaining a more nuanced understanding of intelligence, and getting past crude measures like IQ. He gets a lot of stuff right. Unfortunately, Brooks gets tripped up near the beginning of his column by the Big Fallacy of "heritability." Brooks writes:
"Intelligence is partly hereditary. A meta-analysis by Bernie Devlin of the University of Pittsburgh found that genes account for about 48 percent of the differences in I.Q. scores."
This is just not correct. It's an entirely understandable mistake on Brooks' part, because so many journalists and even scientists are making it. But what statistical studies like Devlin's miss is that genes actually do not pass any complex traits down on their own. The expression and regulation of genes, biologists now understand, is entirely dependent on their interaction with the environment. You cannot separate one from the other. There is no "nature vs. nurture."
Don't take my word for it. Listen to Michael Meaney, Director of the McGill Centre for the Study of Behaviour, Genes and Environment:
"There are no genetic factors that can be studied independently of the environment, and there are no environmental factors that function independently of the genome. Phenotype emerges only from the interaction of gene and environment. The search for main effects is a fool's errand. In the context of modem molecular biology, it is a quest that is without credibility."
Or take a look at this chart and look at all the influence-arrows going in both directions:
The point of the chart is to show how genes are not simple information dispensers, but are dynamic actors in the life of every cell. They don't dictate -- they interact. And how they interact can be affected by just about anything under the sun. Again, Michael Meaney:
"Everything we have learned about molecular biology has shown that gene activity is regulated by the intracellular environment. The intracellular environment is a function of the genetic make-up of the cell and the extracellular environment [which is] also influenced by the environment of the individual."
None of this is yet reflected in how we talk about genetics publicly, thanks in part to this stream of statistical studies that supposedly show what percent of various traits we inherit.
Brooks and the rest of us are victims of the continual and extreme misreading of population studies that seem to show what portion of intelligence comes from genes vs. what portion comes from the environment. When you actually sit down to understand how genetics works, you realize how misleading these studies are. By echoing a strict "nature vs. nurture" sensibility, these heritability estimates are statistical phantoms; they purport to represent something in populations that simply does not exist in actual biology.
If all this has you a little confused, its ok. It should. The ramifications of gene-environment interdependence are so sweeping, it will take a while to come to grips with them. It changes everything we think we understand about "innate," and "hereditary." It opens up a whole new understanding of what human beings are truly capable of. But first we have to describe it correctly. We don't even have right metaphors for genetics to discuss it sensibly in ordinary conversation. That's what I'm spending a good amount of time on now in my book.