The dark side of recent human evolution

Human evolution is well and truly happening. In fact, according to a recently massive genetic study, recent evolution over the past 5,000 years has added a large number of genetic variants associated with diseases to our gene pool.

The study, which was published today in Nature, shows that the massive population growth our species has enjoyed over the past five millennia has not been without cost.

During that time, many mutations, including many are associated with diseases, have entered our gene pool, and because the burgeoning population has spread across the globe, natural selection has not been able to eliminate them.

The study also found that Americans of European descent harboured more of these deleterious genetic variations than Americans of African descent, lending support to the Out-of-Africa model of human history.

According to this model, humans migrated out of Africa in a series of waves, subsequently fanning out through Europe and Asia to settle in all corners of the globe.

The researchers modified this model by proposing massive population growth 5,115 years ago, around the time that agriculture was becoming more widespread and populations began to settle into more fixed locations, to account for the abundance of relatively rare genetic variants that have emerged in recent human evolutionary history.

However, as non-African populations spread apart, with less interbreeding between them, there was less opportunity for negative, or purifying, selection to eliminate deleterious mutations. African populations, however, were more concentrated and the deleterious mutations were eliminated slightly faster.

As such, the deleterious variations in European Americans also emerged more recently than those in African Americans, with the average age of the former being 5,200 years and in the latter being 10,100 years.

The study looked at over 15,000 genes in 6,515 individuals, including 4,298 of European and 2,217of African descent, and found 1.15 million genetic variations in total.

The study not only sheds light on recent human evolution, but also provides a slew of genetic targets that can be used to better understand disease and develop new therapies.

“The recent dramatic increase in human population size, resulting in a deluge of rare functionally important variation, has important implications for understanding and predicting current and future patterns of human disease and evolution,” the authors write.

The paper was published today in Nature.