Human evolution is a “privileged” process?
|January 12, 2014||Posted by News under Evolution, Mind, Neuroscience, News|
Professor Lahn’s research, published this week in the journal Cell, suggests that humans evolved their cognitive abilities not owing to a few sporadic and accidental genetic mutations – as is the usual way with traits in living things – but rather from an enormous number of mutations in a short period of time, acquired though an intense selection process favouring complex cognitive abilities.
The Guardian writer, without perhaps realizing it, goes on to make Bruce Lahn’s proposed evolution sound non-Darwinian, whereas Lahn seems to want to fit it in somehow. Also:
The scientists found that the human brain’s genes had gone through an intense amount of evolution in a short amount of time – a process that far outstripped the evolution of the genes of other animals.
“We’ve proven that there is a big distinction,” Prof Lahn said. “Human evolution is, in fact, a privileged process because it involves a large number of mutations in a large number of genes.
Lahn probably hadn’t got the memo yet about how loaded the concept of privileged is in this context. In any event, he attributed the rapidity of the process to the development of human society, which he says, made selection for intelligence work faster:
“As humans become more social, differences in intelligence will translate into much greater differences in fitness, because you can manipulate your social structure to your advantage,” he said.
The problem is, of course, that the relationship between intelligence and fitness (higher rates of fertile offspring) in humans is something we have been able to observe for a long time. And the results aren’t encouraging.
Millennia of observations have not shown that more intelligent humans produce markedly greater numbers of fertile offspring. As David Stove pointed out in Darwinian Fairytales, it usually works the other way. And, as Richard Dawkins would tell you, that’s the money shot as far as Darwinian evolution is concerned.
From a 2011 interview with Lahn:
BL: Yes. What happens is a random-chance mutation that is advantageous strikes only one individual in a population belonging to a particular species. The person who has that mutation will reproduce a little better. Some of their kids would inherit this mutation and also reproduce a little better because the mutation makes them more attractive, stronger, whatever. Over time, this mutation would spread in the population to the point where it basically takes over the entire population and everybody has it. So we saw, based on comparisons between humans and other species, that signatures of adaptive evolution for these genes meant that they have gone through many of these sweeps. One sweep fixing one advantageous mutation, another sweep comes along and fixes another.
That’s not what the available history shows with human intelligence. But it is how the large Hadron Collider assembled itself, right?
Human evolution is characterized by a dramatic increase in brain size and complexity. To probe its genetic basis, we examined the evolution of genes involved in diverse aspects of nervous system biology. We found that these genes display significantly higher rates of protein evolution in primates than in rodents. Importantly, this trend is most pronounced for the subset of genes implicated in nervous system development. Moreover, within primates, the acceleration of protein evolution is most prominent in the lineage leading from ancestral primates to humans. Thus, the remarkable phenotypic evolution of the human nervous system has a salient molecular correlate, i.e., accelerated evolution of the underlying genes, particularly those linked to nervous system development. In addition to uncovering broad evolutionary trends, our study also identified many candidate genes—most of which are implicated in regulating brain size and behavior—that might have played important roles in the evolution of the human brain. (paywall)
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