I find it very odd that our bodies make vitamin D from sunlight. It seems such a strange primordial thing. And it especially nonsensical because the sun causes so many skin problems. You want just the right dose of sun. It makes me think that it must have been tough to be a caveman, but then again the life expectancy back then was only about 19, so I suppose they had more to worry about than whether they were getting the appropriate amount of sunlight.