The Acceleration of Human Evolution

John Hawks has recently come out with a powerful paper about the Acceleration of Human Evolution. In a recent Blog Post he goes into it.

It is quite simple; the rate of mutations in a population is a linear product of the rate per genome and the population size.

Not all mutations are advantageous, and not all advantageous mutations will be fixed. The vast majority are lost. If a mutation has a selective advantage, then the chance that it will proceed toward fixation (and attain high frequency) is 2s — “s” here is the fitness advantage. That means that 90 percent of new mutations with a 5 percent fitness advantage are simply lost.

The most beneficial mutations are very rare; it is much more likely that a new mutation will be weakly selected. This is another aspect of selection that has been well-known since Fisher. So the chance of fixation increases with s, but the likelihood of the mutation decreases with s — in fact, the number decreases exponentially as selection is stronger and stronger.

If you put all these together, you can predict how many selected changes you should see in a population that has been growing in size. This tells us the number of new adaptive mutations that should come into the population each generation. It is still linear with population size — a larger population should have more mutations in precise proportion to its size.

He goes on:

From that standpoint, the ecological changes documented in human history and the archaeological record create an exceptional situation. Humans faced new selective pressures during the last 40,000 years, related to disease, agricultural diets, sedentism, city life, greater lifespan, and many other ecological changes. This created a need for selection.

Larger population sizes allowed the rapid response to selection — more new adaptive mutations. Together, the the two patterns of historical change have placed humans far from an equilibrium. In that case, we expect that the pace of genetic change due to positive selection should recently have been radically higher than at other times in human evolution.

One Response

  1. […] More on the Acceleration of Human Evolution To keep the excitement going over John Hawks, et al, new paper about the Acceleration of Human Evolution, here’s a link to his “Acceleration Rarely-Asked Questions” about the topic. ( I also blogged about his further explanations of the paper over at The Lyceum.) […]

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