Two Main Bottleneck Events Shaped Modern Human Genetic Diversity

Humans are widely thought to have expanded out Africa starting approximately 50,000 years ago. In this process, genetic variation was reduced the further populations moved away from Africa due to successive bottleneck events. The frequency and nature of these bottleneck events have already been extensively explored in the literature. A recent study, which analyzed 783 microsatellite loci genotyped on 53 globally representative populations, concludes that two major bottleneck events occurred in human history – the first occurring as humans moved out of Africa and the second as humans moved across the Bering Strait into the New World. These events can be detected due to the genetic implications of bottleneck events. After sharp declines in population numbers, excess heterozygosity exists in the population than would be expected given the number of alleles remaining. The authors used the program ‘Bottleneck’ to detect this signature. This study reconfirms the conventional understanding of human expansion.