It's been somewhat of a commonplace, among those who worry about such things, that the increase in the power and complexity of human civilization and culture has reduced the forces of evolution on the species. After all, so one argument goes, we now enable diabetics and others afflicted with genetically-linked physical or mental illnesses to survive and reproduce, where they would have perished back before we came down from the trees. Darwin might have been right, but had become steadily less relevant to our future.
Turns out Darwin is still very much relevant. A just released paper (PDF, of highly technical nature) details a study suggesting that mutations have been accumulating in the collective human genome at a rate that has increased since the 'cultural phase' of the species began. The senior author, John Hawks, is a blogger and has a more approachable summary here.
This result is another byproduct of sequencing of the human genome. As more individual genomes are documented (usually in part), there has been a global effort to collect information on variations in sequence, called the HapMap Project. Some of these variations turn out to be genetic markers for diseases or more innocuous individual traits. Some of them are apparently benign, having little or no impact on the organism.
The variations tend to accumulate at a more or less constant rate over generations of reproduction of the organism, in more or less random locations in the sequence. The accumulation of variations can then be used as a sort of clock. Tracking which variations tend to be inherited together is also a sort of crib on which sections of the genome are actually functional units. If a longish section of such genetic material is found in a population, with few variations, than it was probably a relatively recent introduction to the genome. The more accumulated benign variations, the more likely that it's older. (Yes, I'm simplifying like crazy - follow the links.)
Applying this metric to the growing collection of human genetic variants suggests that new sequences are being introduced to the human genetic pool at a rate atypically high compared to other complex animal species, and that this increase in rate is actually concentrated in the last few tens of thousands of years. (The author has put out a list of 'rarely asked' (i.e., highly technical) questions regarding the analysis, which will be followed by a layman's FAQ on the same site.
The biggest reason for this is one of those 'right under your nose, obvious when pointed out' things - in retrospect. Quoting the paper: "Human populations have vastly increased in numbers during the past 50,000 years or more." More births, more chances for an adaptive mutation that survives. (Note that none of this implies the adaptations are present in all humans.)
Some of these adaptations fall at the far edges of human cultural history. One classic cited in this post about the study is the development of lactose tolerance, which can be dated to about 8,000 years back, and is well-known to be present in only part of the human population. Presumably this conferred an advantage on humans who had already started hanging out with (and eating) herd beasts by allowing them to also drink their milk.
One of the classic situations for evolution at a species level is the 'radiation' into newly available ecological niches of an existing species. Finds like the lactose gene suggest that human cultural variation may have the side effect of creating new kinds of niches - in this case, becoming mildly symbiotic with dairy animals. Of course, talking about all of this as 'rapid' or 'recent' is a relative matter, we are still talking about thousands of years. If we witness such adaptations during our lifetime, it's going to be because they are newly discovered through genomic analysis, not because there was a mutant born next door. However, if this result does makes into popular culture, it may erode the notion that evolution of higher animals is something that only happens on a geological time scale.
The study is also an exhibit of the spread of genomic techniques and results to other fields. Of the five authors, one is from a bioinformatics lab, two are now at commercial genomics company Affymetrix, and two are anthropologists. Digging in the genome may be more rewarding than digging into prehistoric human sites over the new few years. Likely this isn't the last field to be shaken up by the byproducts of reverse-engineering Mother Nature.
(HT: Glenn Reynolds)