Contrary to previous theory, it appears that the rate of human evolution has increased over the last few thousand years (via the San Jose Mercury News):
Until recently, anthropologists believed evolutionary pressures on humans eased after the transition to a more stable agrarian lifestyle. But in the past few years, they realized the opposite was true – diseases swept through societies in which large groups lived in close quarters for a long period.
Natural selection has affected humanity in many ways since the species appeared. My favorite concrete example from the article:
Although children were able to drink milk, they typically developed lactose intolerance as they grew up. But after cattle and goats were domesticated in Europe and yaks and mares were domesticated in Asia, adults with a mutation that allowed them to digest milk had a nutritional advantage over those who didn’t. As a result, they were more likely to have healthy offspring, prompting the mutation to spread, [University of Wisconsin-Madison anthropologist John] Hawks said.
Humans in certain parts of the world have evolved slightly differently due to local conditions, too. This is a tenet of natural selection which often seems to be ignored: If local conditions differ significantly in two regions over a long period of time, a species which exists in both regions will see its two populations diverge as the populations adapt to their local conditions. (This assumes the conditions don’t kill off the population in one region, and also that there’s not significant interbreeding between the populations.)
This is really neat. It’s also good news, because it indicates that the human species is still quite diverse. Why is that good? Because monocultures tend to be a bad thing for a species’ long-term survival, since it makes them more susceptible to individual contagious elements against which they have no defense (such a problem seen in bananas and Microsoft Windows).
The article indicates that the rate of human evolution has increased since we became “domesticated”:
In the past 5,000 to 10,000 years, as agriculture was able to support increasingly large societies, the rate of evolutionary change rose to more than 100 times historical levels, the study concluded.
I have my own idea to add to this: I suspect people have assumed that evolution slowed down because there we tamed many hostile environments, so there were fewer pressures exerting natural selection upon us. Instead, I think that civilization has made our environments more constant and consistent, meaning what pressures there are are more persistent, and so we evolve in more of a straight line due to those pressures, rather than meandering around due to conditions that change every few years (or decades, or centures). With less genetic confusion, what evolution that does occur can occur far more rapidly.
On another, related note, the common wisdom seems to be that language has tended to evolve more slowly since writing and writing became more widespread, since writing fixes spelling and grammar in the mind of the literate population. I don’t know if language is subject to something like natural selection, but there seem to be some parallels there, and this makes me wonder if we’ll find that (for example) English is also evolving more rapidly than we think, just in a more constant direction and a more systematic manner than it used to.