By Harold McGee
When and why did humans extend our biological heritage as milk drinkers to the cultural practice of drinking the milk of other animals? Archaeological evidence suggests that sheep and goats were domesticated in the grasslands and open forest of present-day Iran and Iraq between 8000 and 9000 BCE, a thousand years before the far larger, fiercer cattle. At first these animals would have been kept for meat and skins, but the discovery of milking was a significant advance. Dairy animals could produce the nutritional equivalent of a slaughtered meat animal or more each year for several years, and in manageable daily increments. Dairying is the most efficient means of obtaining nourishment from uncultivated land, and may have been especially important as farming communities spread outward from Southwest Asia.