My suggestion that these neurons provided the initial impetus for "runaway" brain/ culture co-evolution in humans, isn't quite as bizarre as it sounds. Imagine a martian anthropologist was studying human evolution a million years from now. He would be puzzled (like Wallace was) by the relatively sudden emergence of certain mental traits like sophisticated tool use, use of fire, art and "culture" and would try to correlate them (as many anthropologists now do) with purported changes in brain size and anatomy caused by mutations. But unlike them he would also be puzzled by the enormous upheavals and changes that occurred after (say) 19th century — what we call the scientific/industrial revolution. This revolution is, in many ways, much more dramatic (e.g. the sudden emergence of nuclear power, automobiles, air travel, and space travel) than the "great leap forward" that happened 40,000 years ago!!

He might be tempted to argue that there must have been a genetic change and corresponding change in brain anatomy and behavior to account for this second leap forward. (Just as many anthropologists today seek a genetic explanation for the first one.) Yet we know that present one occurred exclusively because of fortuitous environmental circumstances, because Galileo invented the "experimental method," that, together with royal patronage and the invention of the printing press, kicked off the scientific revolution. His experiments and the earlier invention of a sophisticated new language called mathematics in India in the first millennium AD (based on place value notation, zero and the decimal system), set the stage for Newtonian mechanics and the calculus and "the rest is history" as we say.

Now the thing to bear in mind is that none of this need have happened. It certainly did not happen because of a genetic change in the human brains during the renaissance. It happened at least partly because of imitation learning and rapid "cultural" transmission of knowledge. (Indeed one could almost argue that there was a greater behavioral/cognitive difference between pre-18th century and post 20th century humans than between Homo Erectus and archaic Homo Sapiens. Unless he knew better our Martian ethologist may conclude that there was a bigger genetic difference between the first two groups than the latter two species!)