After the last ice age, people moved north farther away from the sun. That means less Vitamin D. You get Vitamin D from the sun, plants get Vitamin D from the sun. Vitamin D darkens the skin, so the one kid in the family who happened to have lighter skin had a slightly better chance of surviving a disease called rickets. Eventually, we get white people. That's why today, light-skinned people near the sun get skin cancer and dark-skinned people away from the sun get rickets.
My point, and I have one, is this: If the Klan would drink their milk, we wouldn't be in the mess we're in now.