[TheAdamAndChe]

Really? I thought selective pressure was required to cause a major shift in the average human. The reason that our population has boomed is because our selective pressure has declined significantly. Or are you more talking about the adaptability of the species overall has increased?

[danieltillett]

Evolution acts on genetic diversity present in the population. The rate at which new genes (mutations) appear is basically a constant proportional to the population size (i.e. double the population and you double the rate new genes are formed). The rate at which new genes under positive selection spread through the population is approximantly equal to the log of the population size. This means it only taken 3x longer for a new gene to spread through a population of 100 million as it does to spread through a population of 1 million.

The end result is the bigger the population the more evolution even if in a static environment most of the evolution is invisible. Of course the environment of farmers is very different to hunter-gathers so there has been a large amount of visible evolution in the last 5000 years.

[perl4ever]

In a booming population, it seems to me that evolution can be more rapid in "selection" with less "pressure". For instance, if humans start exploring a new continent, some might have 10 times the normal number of grandchildren, and their genes would rapidly outnumber the others. Whereas if population is static, then you could say there's more "pressure" but there's probably less "selection", because there's less opportunity and variance in success.