In the DNA of a group of 5,000-year-old skeletons from Germany, they discovered no trace of the lactase allele, even though it had originated a good 3,000 years beforehand. Similar tests done on 3,000-year-old skeletons from Ukraine showed a 30 percent frequency of the allele. In the modern populations of both locales, the frequency is around 90 percent.
I thought I was on top of the literature, but this was new to me. It’s even more proof that human evolution did not stop with the advent of Homo sapiens. It has continued … even after the transition from prehistory to history!
The same article also has some thoughts from Bruce Lahn, the evolutionary geneticist who has mapped human variation at two genes, ASPM and microcephalin, that seem to regulate the growth of brain tissue.
Even if Lahn could prove to everyone's satisfaction that ASPM and microcephalin are under selection, whether intelligence is the trait being selected for would be far from a settled question. It could be, as Lahn suggested, that some other mental trait is being selected, or that the activity of ASPM and microcephalin in other parts of the body is what is under selection. More work will certainly be done. But one can speculate with far more confidence about what drove the dramatic increase in intelligence attested by the fossil record: the advent of human culture.
"Intelligence builds on top of intelligence," says Lahn. "[Culture] creates a stringent selection regime for enhanced intelligence. This is a positive feedback loop, I would think." Increasing intelligence increases the complexity of culture, which pressures intelligence levels to rise, which creates a more complex culture, and so on. Culture is not an escape from conditioning environments. It is an environment of a different kind.
Reference
Phelan, B. (2008). How we evolve. A growing number of scientists argue that human culture itself has become the foremost agent of biological change. Seed Posted October 7, 2008