Somehow there was an Oliver Sacks book that I missed. This one is about him going to a series of tropical islands to look at 1. a group of people who all have a similar achromatopsia, and 2. bunch of people who have a Parkinsonian-like disease of unknown etiology, and 3. cycads. This is an older book that he’s updated with a series of lengthy and interesting end notes. It’s more like three separate essays with a small thread between them. More questions than answers, but I liked being in the tropics with him for a bit.