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Determined to be different: what we do changes the wiring of our genes

Genetic change in humans is driven by cultural change, for example, blue eyes. Corey Butler

The human genome provides penetrating and unexpected insights into human individual and collective history. Among them is the counterintuitive idea that genes are at the mercy of experience – that what we do in our lives affects which genes are switched on and off.

A stressful experience, for example, can make you more vulnerable to infection, because stress hormones indirectly alter the switches that control the expression of genes.

So, far from genes being the cause of how we act, the new understanding sees them as just as much a consequence of how we act. This subtler view of genes has yet to colonise the popular imagination.

On a much longer, evolutionary timescale, the same reversal of causation is necessary.

We now know that many genetic changes in human beings are driven by cultural ones, at least as much as the other way round.

For example, the ability to digest lactose as adults spread among Africans and Europeans because of dairy farming, rather than vice versa.

Blue eyes may be a consequence of the invention of agriculture. Reliance on grain in sunless northern climates led to vitamin D deficiency because grain is lower in vitamin D compared with traditional diets of fish, meat, berries, etc. So people eating bread as a staple got less vitamin D in their diet.

Another source of vitamin D is sunlight. Mutations making skin paler would enable sunshine to be more easily absorbed, making up for the decrease of vitamin D in these northern climate diets. One of the mutations that made skin paler had the side effect of making eyes paler, and bluer.

This not Lamarckism; it is Darwinism, because it still depends on selection among random mutations.

If we take this nature-via-nurture idea seriously, and put the cultural horse before the genetic cart, then an upside-down view of human uniqueness emerges.

Genes that facilitate language may be the consequence, as much as the cause, of speech.

This radically alters the way we should look at the “human revolution” – the relatively sudden transformation of African hominid apes to fully modern human beings around 100,000 years ago.

Instead of seeking some genetic mutation that triggered this transformation, we should instead consider a cultural trigger.

What was the key cultural mutation?

Culture is itself dominated by the Darwinian trio of replication, variation and selection.

The explosive take-off of human technology and prosperity over the past 100,000 years can be traced back to a particular cultural invention – exchange – which happened some time before 120,000 years ago (when man-made objects first started moving long-distances through trade).

This had the same impact on cultural evolution that sex had on biological evolution.

Just as sex made evolution cumulative, by enabling individuals to pass on mutations to their descendants, the invention of exchange – swapping one thing for another – enabled people to draw on the inventiveness of strangers.

This meant technology could begin to embody combinations of new ideas, drawn from different places and times through the medium of exchange.

The result was a self-reinforcing cycle of exchange and specialisation: the more people exchanged, the more they specialised and vice versa.

As a result, the human lifestyle moved with increasing speed away from individual self sufficiency and towards mutual interdependence, shared innovation and collective intelligence.

Today nobody even knows how to make a pencil (the person who mines graphite does not know how to fell trees), because the knowledge is stored among brains rather than in them.

History plainly shows that the bigger the exchange network, the more rapid the rate of technological change. Conversely, if people are isolated from exchange networks, their innovation rate slows – as happened in China under the Ming empire, for example.

If societies are completely isolated, innovation may even go into reverse and technologies start to be discarded – as happened in Tasmania after it became an island 10,000 years ago.

The implications of this way of seeing human society is that the bottom-up evolution of human technology and society is inevitable, inexorable and potentially infinite, but its rate depends on the degree integration of human minds into a collective brain by exchange networks.

Or to put it another way, human prosperity depends upon ideas having sex. The internet, by connecting human minds all over the world, can only accelerate innovation.

Matt Ridley will present the opening keynote speech of The University of Melbourne’s Festival of Ideas on Monday.

See our other Festival of Ideas coverage: We’ve cracked the genetic code, now what? by David Weisbrot

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