[danieltillett]

Speed of evolutionary change is basically proportional to the population size. Thanks to the huge increase in population size after the rise of agriculture, more human evolution has happened in the last 5000 years than the previous 500,000.

[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.

[sgt101]

I think that depends on pressures and variation as well; without selection pressure I don't think that there is a reason why the variation in the overall population will change.

[rocqua]

There are still selection pressures, only they are more focused on sexual selection rather than survival selection. There still remain advantages to being smart healthy and athletic. What has changed is the lower bound on these required for survival. What has happened to pressures on these required for reproduction seems like a much harder to judge question.

Certainly though, those with advantageous mutations seem to have a better chance of reproduction.

[taneq]

Selection pressure doesn't just mean people being killed by things. Some groups having significantly more surviving offspring is also a selective pressure.