In an article in this week's Science Journal, scientists Simon E. Fisher and Matt Ridley make a case for some aspects of human genetic evolution in the last 200,000 years to be the consequence of cultural evolution rather than, as is generally assumed, cultural evolution to be the consequence of genetic mutation.AbstractThey cite examples such as Richard Wrangham's study showing how the discovery of cooking led to a change in the size of the human gut, the spread of the lactase-persistence gene facilitated by the availability of cattle milk as a consequence of cattle-herding about which I have previously blogged in Lacatose Tolerance and Creation 'Science' and higher alcohol tolerance among Europeans as a result of greater alcohol consumption in Europe, as compared to Asians.
State-of-the-art DNA sequencing is providing ever more detailed insights into the genomes of humans, extant apes, and even extinct hominins (1–3), offering unprecedented opportunities to uncover the molecular variants that make us human. 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. For example, Klein has argued that the dawn of human culture stemmed from a single genetic change that “fostered the uniquely modern ability to adapt to a remarkable range of natural and social circumstance” (4). But are evolutionary changes in our genome a cause or a consequence of cultural innovation.
The authors suggest that the "human revolution", when humans developed a range of abilities, mostly cultural, which distinguish us most radically from other animals, even our closest relatives, may have been led by cultural changes rather than, as is normally assumed, caused by genetic evolution. They point out how this shows the difficulty in distinguishing between cause and effect in human evolution.
But is this dispute between culture-led and gene-led evolution more than a storm in a teacup? Is it not in fact exactly what we would expect?
Ever since Richard Dawkins proposed the idea of 'memes' - memory genes or units of cultural inheritance - being inherited replicators subject to imperfect replication, just like genes, and so being the subject of Darwinian evolution, people have speculated on human gene-meme co-evolution. Dawkins himself pointed out how genes form alliances with other genes when they are mutually beneficial and how genes have no concern for the nature of the replicators with which they form these alliances. There is no intent involved; the alliances are merely consequences of groups of replicators being more successful in the presence of certain other replicators. In fact, there is no mechanism for distinguishing between memetic and genetic replicators. What ever works to produce more descendants will produce more descendants with those replicators.
In several blogs I have pointed out how the information in genes only has meaning in the context of the environment in which they find themselves, and it is the meaning which matters. In the presence of a surplus of cattle milk, humans were able to sustain a larger population, and have more babies due to earlier cessation of breast feeding (which acts as a natural contraceptive) if they carried the lactase-persistence mutation, whereas, in the absence of cattle milk (due to tsetse fly making cattle-herding non-viable, for example) there was an advantage in weaning babies at about 18 months, when lactose intolerance normally develops. The meme or memeplex of cattle-herding created an environment in which the lactase-persistence mutation produced more descendants.
There are several more examples of cultural change facilitating genetic evolution in humans, such as the movement of Han Chinese onto the Tibetan plateau leading to genetic changes associated with living in a high altitude, and the evolution of the ability to tolerate alcohol, leading to the Asian facial 'flush' which followed the spread of rice farming between 7-10,000 years ago.
The "Human revolution" seems to have been the evolution of the ability to adapt to new situations and to form corresponding cultures and the ability to learn and pass on these cultures in the form of memes. In other words, the "Human revolution" of about 200,000 years ago appears to have been the evolution of memes, or rather the evolution of the ability to pass on and inherit memes, arising out of the need of early humans to work together as cooperative groups.
As with the evolution of anything involving multiple replicators, it's immaterial and only of academic interest which one in particular led the change. Just so when those replicators include memes in a gene-meme complex.
Reference:
Culture, Genes, and the Human Revolution
Simon E. Fisher and Matt Ridley
Science 24 May 2013: 340 (6135), 929-930. [DOI:10.1126/science.1236171]
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