Islands as Natural Laboratories for Evolution
Oliver Sacks’s exploration of the intersection between geography and neurology stems from a lifelong obsession with islands. This fascination, which began with childhood memories of the Isle of Wight and stories of legendary mariners, evolved from a romantic interest into a scientific curiosity. Islands serve as unique experiments of nature where geographic isolation forces life to take separate evolutionary paths. This process can produce singular species, like the lemurs of Madagascar or the giant tortoises of the Galapagos, but it can also create unique human communities defined by shared biological traits.
The concept of a world without color first intrigued Sacks through personal experiences with visual migraines, which caused temporary losses of color perception. His interest deepened after he treated a painter who, following a brain injury, lost his ability to see, imagine, or even dream in color. While this patient felt his world was impoverished, Sacks wondered about those born without any color vision at all. This condition, congenital achromatopsia, is extremely rare globally, affecting individuals who lack functioning cones in their retinas—the cells responsible for color and fine detail. Instead, they rely entirely on their rods, which are typically used for seeing in low light.
History provides examples of how isolated communities can adapt to shared sensory differences. On Martha’s Vineyard in the 18th and 19th centuries, a high incidence of hereditary deafness led to a unique culture where everyone, hearing and deaf alike, used sign language. This environment meant that being deaf was not a disability but a different way of being. Sacks wondered if a similar "country of the colorblind" existed and his search led him to Pingelap, a tiny atoll in Micronesia where nearly ten percent of the population carries the gene for total colorblindness.
To investigate this community, Sacks organized an expedition with an ophthalmologist and a Norwegian scientist named Knut Nordby, who provided a unique perspective because he was born with achromatopsia. Despite his lack of color vision, Nordby became an expert in the physics of sight. His experience illustrated the practical realities of the condition: because he relied on rods, bright daylight was physically painful and blinding, a struggle known as photophobia. He required heavy dark glasses to function outdoors and used magnifying lenses to compensate for low visual sharpness. However, in dim light, he was more adept than those with normal vision. He did not feel his world was incomplete; instead, he had developed a heightened sensitivity to texture, tone, movement, and depth, perceiving his surroundings like a highly detailed black-and-white photograph.
The journey to Pingelap required traveling through the vast Pacific, a region shaped by ancient migrations and modern military intervention. The team stopped at Johnston Atoll, a restricted military site used for nuclear testing and chemical weapons storage, which had been transformed from a bird sanctuary into a toxic environment. Further stops in the Marshall Islands revealed the complex legacy of Western influence. On Majuro and Kwajalein, they observed the consequences of military occupation and the introduction of Western diets, which had replaced traditional foods and led to high rates of diabetes and heart disease. The region was also haunted by the history of nuclear testing, which had left several atolls radioactive and uninhabitable, displacing entire populations.
Amidst these grim realities, the travelers remained focused on the biological and human mysteries of the islands. As they moved toward Pohnpei, a lush volcanic island that served as the gateway to Pingelap, the physical beauty of the landscape contrasted sharply with the flat coral atolls they had previously visited. The expedition was not merely a search for a medical anomaly but an attempt to understand how a community adapts when a specific trait, usually viewed as a defect, becomes a common part of the social fabric.
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