A common assumption is that the emergence of behaviorally modern humans after 200,000 years ago required—and followed—a specific biological change triggered by one or more genetic mutations. [...]
This prevailing logic in the field may put the cart before the horse. The discovery of any genetic mutation that coincided with the “human revolution” (6) must take care to distinguish cause from effect. Supposedly momentous changes in our genome may sometimes be a consequence of cultural innovation.
In certain cases this is obvious. Lactase-persistence mutations did not trigger dairy farming; they spread as an evolutionary response to dairy consumption. The higher alcohol tolerance of Europeans relative to Asians did not prompt, but followed, greater alcohol consumption in Europe. [...]
Under the culture-driven view, many critical genomic alterations that facilitated spoken language, for example, might have spread through our ancestors after this trait emerged. That is, prior behavioral changes of the species provide a permissive environment in which the functionally relevant genomic changes accumulate. The selective advantage of a genetic change that increased language proficiency would likely be greatest in a population that was already using language.
This is an entirely traditional and common-sensical view, corresponding to the position advanced more than twenty years ago in Steven Pinker and Paul Bloom, "Natural language and natural selection", Behavioral and Brain Sciences, December 1990.
For universal grammar to have evolved by Darwinian natural selection it is not enough that it be useful in some general sense. There must have been genetic variation among individuals in their grammatical competence. There must have been a series of steps leading from no language at all to language as we now find it, each step small enough to have been produced by a random mutation or recombination, and each intermediate grammar useful to its possessor. Every detail of grammatical competence that we wish to ascribe to selection must have conferred a reproductive advantage on its speakers, and this advantage must be large enough to have become fixed in the ancestral population. And there must be enough evolutionary time and genomic space separating our species from nonlinguistic primate ancestors.
But the old and impeccable pedigree of this classical account of gene-culture co-evolution, in the origins of language and elsewhere, has not prevented the spread of "gene for X" bizarreness, or other forms of anti-evolutionary mysticism. So it's nice to see a couple of eminent scientists expressing these ideas, clearly and forcefully, in the pages of a widely-read journal.