People who have no cones at all, and are genuinely color-blind, are called achromatopes. People who are “color-blind” normally lack one of the three types of cones, so they don’t see all the colors, just some of them. “Our eyes contain two types of photoreceptors for vision-rods, which help us see in dim conditions but provide no color, and cones, which work when the light is bright and divide the world up into three colors: blue, green, and red. You might have heard her referred to as Mitochondrial Eve.
Over time, the mitochondrial pool for humans has shrunk so much that, almost unbelievably but rather wonderfully, we are all now descended from a single mitochondrial ancestor-a woman who lived in Africa about 200,000 years ago.
In consequence, the human mitochondrial pool shrinks a little with every generation because of these localized extinctions. All her descendants will still have mitochondria, but it will come from other mothers on other genetic lines. So if a woman has only sons or no children at all-and that happens quite often, of course-her personal mitochondrial line will die with her. A woman endows all her children with her mitochondria, but only her daughters have the mechanism to pass it onward to future generations. Such a system means that there will be many extinctions along the way. “Sperm pass on none of their mitochondria during conception, so all mitochondrial information is transferred from generation to generation through mothers alone. And yet look how many people have been enslaved or hated or lynched or deprived of fundamental rights through history because of the color of their skin.” Biologically, there is actually no such thing as race-nothing in terms of skin color, facial features, hair type, bone structure, or anything else that is a defining quality among peoples. “People act as if skin color is a determinant of character when all it is is a reaction to sunlight. “It is extraordinary how such a small facet of our composition is given so much importance,” she said. That’s all that race is-a sliver of epidermis.” I mentioned this to Nina Jablonski when we met in her office in State College, Pennsylvania, soon afterward. “That,” he said, “is where all your skin color is. “One of the most memorably unexpected events I experienced in the course of doing this book came in a dissection room at the University of Nottingham in England when a professor and surgeon named Ben Ollivere (about whom much more in due course) gently incised and peeled back a sliver of skin about a millimeter thick from the arm of a cadaver.
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