@JLeslie. OK. I shall re-word it. The lighter the skin the better the chances of the offspring surviving (rickets is a killer child-hood disease.) So, over a period of several thousand years, natural selection favored lighter skin, the lighter the better, the lighter the more survived, so eventually the white race came into being.
In modern times they add vitamin D (and iodine and other vitamins and minerals) to our food (read the labels.) We don’t need to rely on our skin being exposed to help us synthesize it naturally. If we did, those poor kids with that illness who can never, ever go into any sunlight wouldn’t stand a chance. But rickets is the least of their worries, thanks to modern technology and medicine.
@john65pennington Here
“American researchers Elmer McCollum and Marguerite Davis in 1913 discovered a substance in cod liver oil which later was called “vitamin A”. British doctor Edward Mellanby noticed dogs that were fed cod liver oil did not develop rickets and concluded vitamin A, or a closely associated factor, could prevent the disease. In 1921, Elmer McCollum tested modified cod liver oil in which the vitamin A had been destroyed. The modified oil cured the sick dogs, so McCollum concluded the factor in cod liver oil which cured rickets was distinct from vitamin A. He called it vitamin D because it was the fourth vitamin to be named.[16][17][18] It was not initially realized that, unlike other vitamins, vitamin D can be synthesised by humans through exposure to UV light.
In 1923, it was established that when 7-dehydrocholesterol is irradiated with light, a form of a fat-soluble vitamin is produced (now known as D3). Alfred Fabian Hess showed “light equals vitamin D.”[19] Adolf Windaus, at the University of Göttingen in Germany, received the Nobel Prize in Chemistry in 1928, for his work on the constitution of sterols and their connection with vitamins.[20] In the 1930s he clarified further the chemical structure of vitamin D.[21]
In 1923, Harry Steenbock at the University of Wisconsin demonstrated that irradiation by ultraviolet light increased the vitamin D content of foods and other organic materials.[22] After irradiating rodent food, Steenbock discovered the rodents were cured of rickets. A vitamin D deficiency is a known cause of rickets. Using $300 of his own money, Steenbock patented his invention. His irradiation technique was used for foodstuffs, most memorably for milk. By the expiration of his patent in 1945, rickets had been all but eliminated in the US.[23]“_
Long story short….lotsa people out there WAY smarter than us!!: