“All mammals nurse their young, and breast milk benefits a newborn infant in ways above and beyond nutrition. In fact, until 1 to 2 years of age, the American Academy of Pediatrics, the World Health Organization, the Institute of Medicine and more promote breast-feeding as optimal. Unfortunately, breast-feeding until that age is often difficult, if not impossible, because mothers have to return to work, and children go off to preschool or day care. So we often replace human milk with the milk of cows or other animals. But at a certain point, we have to acknowledge that we are the only mammals on the planet that continue to consume milk after childhood, often in great amounts. More and more evidence is surfacing, however, that milk consumption may not only be unhelpful, it might also be detrimental. … there’s very little evidence that most adults need it. There’s also very little evidence that it’s doing them much good.”

"Got Milk? Might Not Be Doing You Much Good", in The New York Times (17 November 2014) http://www.nytimes.com/2014/11/18/upshot/got-milk-might-not-be-doing-you-much-good.html?_r=0