Population bottlenecks were common throughout human history

From contemporary and ancient DNA, UC Berkeley researchers estimated when population bottlenecks occurred for several hundred groups around the world and throughout recent human history. The colors indicate the number of generations the bottleneck or founder event preceded the individuals whose DNA was sequenced. (Graphic courtesy of Rémi Tournebize, UC Berkeley) Human populations have waxed and waned over the millennia, with some cultures exploding and migrating to new areas or new continents, others dropping to such low numbers that their genetic diversity plummeted. In some small populations, inbreeding causes once rare genetic diseases to become common, despite their deleterious effects. A new analysis of more than 4,000 ancient and contemporary human genomes shows how common such "founder events" were in our history. A founder event is when a small number of ancestral individuals gives rise to a large fraction of the population, often because war, famine or disease drastically reduced the population, but also because of geographic isolation - on islands, for example - or cultural practices, as among Ashkenazi Jews or the Amish. More than half of the 460 groups represented by these individuals had experienced a population bottleneck somewhere in their past that decreased their genetic diversity and likely increased the incidence of recessive hereditary diseases.