'The central problem is that people don't understand what "heritable" or "genetic" really means.'
Apparently so. Heritability does not mean genetic causation. Language is extremely heritable (that is, children almost always speak the same language as their parents), and not because there's a long just-so chain of genetic and hormone events that ends in an innate facility for Cantonese.
"Heritability" means something like "how much of the variation in a population is due to genetic differences". This leads to some odd results, e.g. number of arms has low heritability (almost all variation is due to environment).
Anyway, language is not heritable. The variation in the languages people speak in a population is not due to genes but rather to environmental effects.
That's true, but having said that, there are alleles that affect the nature of the language people speak. So there are alleles that give onre better facility at speaking tonal languages, and those alleles are (surprise, surprise) more common among populations that speak tonal languages (such as Chinese).
Apparently so. Heritability does not mean genetic causation. Language is extremely heritable (that is, children almost always speak the same language as their parents), and not because there's a long just-so chain of genetic and hormone events that ends in an innate facility for Cantonese.