Cosma Shalizi has written a two part dialog that is amazingly well in line with my own thoughts on the subject of the heritability of intelligence: g is a statistical artifact, we have brains that evolved for plasticity, not specificity, and that while many behavioral traits have a heritable component, it’s not anything like what the naive extremists among the cognitive science crowd think. There are no genes that specify what you will name your dog — in fact, most of the genes associated with the brain have very wide patterns of expression and functions that are not neatly tied to behaviors: how does an allele of an adhesion factor map to your performance on a math test? It doesn’t, not directly.
Cosma has a wonderful example of the heritability of accents to illustrate the complications of trying to assign a genetic cause to properties associated with race and class and ethnicity. They may look like they’re genetically determined, but they aren’t. In my own family, I noticed a weird phenomenon: my grandparents came from Minnesota, and my mother was born there but moved to Washington state as a child. My grandparents had that Scandinavian-influenced upper midwest accent (if you’ve seen the movie Fargo, you’ve heard an amplified version of the same—most Minnesotans have only hints of that degree of an accent). My mother doesn’t have it. Oddly, though, I’ve heard bits of it in my sisters’ accents, an attenuated version of the already mild Minnesota sing-song, while my brothers and I don’t have a trace of it. I was tempted to speculate that there was a dominant Scandihoovian allele located on the X chromosome, but I suspect the more likely culprit would be sex differences in the influence of maternal and paternal families on boys and girls. That’s harder to tease apart than something as discrete as a gene, though, and it’s also a fuzzy effect that can be affected by scientific scrutiny.
Unfortunately, Three-Toed Sloth doesn’t have a comments section, so if you want to argue about it all, here’s a convenient battle ground in a Pharyngula thread.