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In 1775, a typhoon struck the atoll of Pingelap in the Pacific Ocean, leaving as few as 20 survivors – one of whom was King. Hundreds of years later, this population bottleneck would be the cause of total colorblindness in a significant number of the population.
Colorblindness – as most people understand it – is the decreased ability to see colors or differences in color. Green-red color blindness affects around 8 percent of men and 0.5 percent of women with Northern European ancestry, according to the National Eye Institute. However, on the atoll of Pingelap, around 10 percent have a much rarer condition known as complete achromatopsia, or total color blindness.
People with the condition cannot see any colors, seeing only in black, white, and gray, due to a complete absence of functional color-perceiving cones. As well as this, people with complete achromatopsia may also experience sensitivity to light, reduced sharpness of vision, and involuntary movements of the eye. What the people of Pingelap have is an extremely rare condition.
Back to the typhoon and the king. When the typhoon of 1775 wiped out almost all of the already quite small population of Pingelap, 19 islanders were left on the atoll with their King. As well as this being an awkward subject to King ratio, it would end up causing the island's vision problems, as it's likely that he had a recessive gene that caused the condition.
"Two brothers in sibship 1067 left survivors of Typhoon Lengkieki. Semenuhwe had one child, while Mwahuele left seven children by three wives, one of whom married a cousin, the daughter of Semenuhwe," a paper published in the American Journal of Human Genetics reads.
"Most probably the gene was present but rare before Typhoon Lengkieki, descending from an earlier mutation, and by chance was transmitted through Mwahuele to several of the few survivors."
With so few people on the atoll, a lot of inbreeding took place, and the gene became prevalent in the population. It affects about 1 in 30,000 people worldwide, but up to 10 percent of the population of Pingelap.
