Most adults once could not digest milk until a mutation changed that
Originally, only children could digest milk. Adults stopped making lactase, the enzyme that breaks down milk sugar, so early herders turned milk into cheese and curd to lower the lactose. Then, millennia ago, a random genetic change took hold among people in northwestern Europe, letting grown-ups drink it as a backup food source.
Milk is made by the mammary glands of mammals to feed their young before they can handle solid food. It carries calcium, protein, saturated fat and lactose, a sugar found almost nowhere else, possibly only in forsythia flowers and a few tropical shrubs. The first milk after birth, colostrum, is packed with antibodies and growth factors that protect the newborn. The word traces back through Old English to a Proto-Germanic root shared with German Milch and Dutch melk.
In humans, lactase peaks in the small intestine right after birth and then slowly declines unless milk stays in the diet. Adults who keep digesting it rely on lactase persistence; others are lactose intolerant. Groups that could tolerate milk became inventive, milking not only cattle but sheep, goats, yaks, water buffalo, horses, reindeer and camels, and turning it into butter, yogurt, kefir and cheese.
Dairying began after animals were domesticated, independently in several places, from roughly 9000 to 7000 BC in Mesopotamia to 3500 to 3000 BC in the Americas. Cattle, sheep and goats were first tamed in Southwest Asia. The archaeologist Andrew Sherratt argued that people kept animals for meat first and only later, in the fourth millennium BC, started milking them. Fat residues in ancient pottery have undercut that idea, showing that farmers in Southwest Asia were already milking animals no later than the seventh millennium BC.
The scale today is enormous. In 2011, about 260 million dairy cows produced some 730 million tonnes of milk. India is the largest producer, leading in both cow and buffalo milk, while New Zealand, Germany and the Netherlands export the most dairy products. More than six billion people consume milk or milk products, and between 750 and 900 million live in dairy-farming households. Since 1961 the Codex Alimentarius has defined milk as an animal's normal mammary secretion with nothing added or taken away.
Source: Milk
