## 15-20 people is viable as a small colony but it's ... not great. - The island of Pingelap also suffered a population bottleneck in 1775 following a typhoon that had reduced the population to only 20 people. As a result, complete achromatopsia has a current rate of occurrence of roughly 10%, with an additional 30% being carriers of this recessive condition. - Around 1814, a small group of British colonists founded a settlement on Tristan da Cunha, a group of small islands in the Atlantic Ocean, midway between Africa and South America. One of the early colonists apparently carried a rare, recessive allele for retinitis pigmentosa, a progressive form of blindness that afflicts homozygous individuals. As late as 1961, the majority of the genes in the gene pool on Tristan were still derived from 15 original ancestors; as a consequence of the inbreeding, of 232 people tested in 1961, four were suffering from retinitis pigmentosa. This represents a prevalence of 1 in 58, compared with a worldwide prevalence of around 1 in 4,000 ## Further Reading - [[backup_before_conversion/2020.07.20 Inbreeding]] - [[2021-05-31 Settlements]]