It was already known by archaeological and historical research that human development has taken a huge flight in the last thousands of years. A new look on the human genome reveals that most of the genetic features people carry nowadays, have actually evolved in the last 5,000 years or so. This seems like a long time, but it’s only 5 percent of the total time that mankind wandered around on the earth already. This is mainly due to developments in agriculture, which enabled the enormous explosion of human populations. The number of humans increased from a few million individuals to more than 7 billion people nowadays.
Researchers examined more than 15,000 genes in each of 6,515 people of European-American or African-American ancestry, looking for genetic variants. Of these 15,000, the European-Americans shared 709,816 genetic variants. More than 81 percent of these arose in the past 5,000 years, the researchers determined. African-Americans in the study collectively carried 643,128 genetic variants, of which more than 58 percent are less than 5,000 years old.
Obviously, the genetic variance in the European-American population increased more strongly. On top of that, in European-Americans, variants predicted to have harmful effects tend to be younger than those in African-Americans. In European-Americans these are about 3,000 years old, versus 6,200 years old in African-Americans. The main cause for these differences, again, lies in the speed of population growth: African populations have grown in recent millennia, but not as much as populations outside Africa, which went from zero to billions in less than 100,000 years. Evolution has not had time to purge the newest harmful changes in either group, and many of them pack a wallop in terms of disease risk.
So next to more knowledge on the human evolutionary history, this research also gives new insights in the general strength and health of the human population. As researcher Joshua M. Akey points out though: “It’s hard to speculate on the genetic health of our species when the environment is changing,” he says. “We’ll have to check back in a few thousand years.” But, he adds, one thing is for certain: “If we stop changing, we’re evolutionarily dead.”
W. Fu et al. ‘Analysis of 6,515 exomes reveals the recent origin of most human protein-coding variants.’ Nature. Published online: November 28, 2012. doi:10.1038/nature11690