Skin colour is a poor dividing line between populations, though maybe on this vitamin D issue it might be more reasonable. There is no "black race." There are populations of various African origins, a much more complex and messier situation that the category "race" obscures. There is statistically more genetic diversity _within_ Africa than in the entire human population outside of Africa, so drawing a cline based on some "black" or "African" or "Negroid" basket of traits is fully 19th century quackery.
EDIT Put another way: "race" is a cultural category, with little biological meaning. The key question here is vitamin D responses in southern-adapted vs. northern lattitude adapted population groups.
Skin colour is a poor dividing line between populations, though maybe on this vitamin D issue it might be more reasonable. There is no "black race." There are populations of various African origins, a much more complex and messier situation that the category "race" obscures. There is statistically more genetic diversity _within_ Africa than in the entire human population outside of Africa, so drawing a cline based on some "black" or "African" or "Negroid" basket of traits is fully 19th century quackery.
EDIT Put another way: "race" is a cultural category, with little biological meaning. The key question here is vitamin D responses in southern-adapted vs. northern lattitude adapted population groups.