I’ve been reading more of Matt Ridley’s The Evolution of Everything, from which a previous excerpt can be found here, here.  It continues to be very good.  In this bit, Ridley discusses the relationship between genetic and cultural evolution:

What sparked the human revolution in Africa?  It is an almost impossibly difficult question to answer, because of the very gradual beginning of the process: the initial trigger may have been very small. The first stirrings of different tools in parts of east Africa seem to be up to 300,000 years old, so by modern standards the change was happening with glacial slowness.  And that’s a clue.  The defining feature is not culture, for plenty of animals have culture, in the sense of traditions that are passed on by learning.  The defining feature is cumulative culture - the capacity to add innovations without losing old habits.  In this sense, the human revolution was not a revolution at all, but a very, very slow cumulative change, which steadily gathered pace, accelerating towards today’s near-singularity of incessant and multifarious innovation.

It was cultural evolution. I think the change was kicked off by the habit of exchange and specialisation, which feeds upon itself - the more you exchange, the more value there is in specialisation, and vice versa - and tends to breed innovation.  Most people prefer to think it was language that was the cause of the change.  Again, language would build upon itself: the more you can speak the more there is to say.  The problem with this theory, however, is that genetics suggests Neanderthals had already undergone the linguistic revolution hundreds of thousands of years earlier - with certain versions of genes related to languages sweeping through the species.  So if language was the trigger, why did the revolution not happen earlier, and to Neanderthals too?  Others think that some aspect of human cognition must have been different in these first ‘behaviourally modern humans’: forward planning, or conscious imitation, say.  But what caused language, or exchange, or forethought, to start when and where it did?

Almost everybody answers this question in biological terms: a mutation in some gene, altering some aspect of brain structure, gave our ancestors a new skill, which enabled them to build a culture that became cumulative.  Richard Klein, for instance, talks of a single genetic change that ‘fostered the uniquely modern ability to adapt to a remarkable range of natural and social circumstance’.  Others have spoken of alterations in the size, wiring and physiology of the human brain to make possible everything from language and tool use to science and art.  Others suggest that a small number of mutations, altering the structure or expression of developmental regulatory genes, were what triggered a cultural explosion.  The evolutionary geneticist Svante Pääbo says: ‘If there is a genetic underpinning to this cultural and technological explosion, as I’m sure there is .. .’

I am not sure there is a genetic underpinning. Or rather, I think they all have it backwards, and are putting the cart before the horse.  I think it is wrong to assume that complex cognition is what makes human beings uniquely capable of cumulative cultural evolution.  Rather, it is the other way around.  Cultural evolution drove the changes in cognition that are embedded in our genes.  The changes in genes are the consequences of cultural changes.  Remember the example of the ability to digest milk in adults, which is unknown in other mammals, but common among people of European and east African origin. The genetic change was a response to the cultural change. This happened about 5,000-8,000 years ago. The geneticist Simon Fisher and I argued that the same must have been true for other features of human culture that appeared long before that.  The genetic mutations associated with facilitating our skill with language - which show evidence of ‘selective sweeps’ in the past few hundred thousand years, implying that they spread rapidly through the species - were unlikely to be the triggers that caused us to speak; but were more likely the genetic responses to the fact that we were speaking.  Only in a language-using animal would the ability to use language more fluently be an advantage.  So we will search in vain for the biological trigger of the human revolution in Africa 200,000 years ago, for all we will find is biological responses to culture.  The fortuitous adopting of a habit, through force of circumstance, by a certain tribe might have been enough to select for genes that made the members of that tribe better at speaking, exchanging, planning or innovating.  In people, genes are probably the slaves, not the masters, of culture.