For those of us who still drink milk and like it and have no trouble digesting it in any of its glorious guises, from butter to yoghurt... here's an intersting blog by Dave Munger at SEED on current scientific thinking/speculation about why some of us can tolerate milk and others can't. Northern Europeans and Africans generally fare well. Southern Euros and East Asians, not so.
One analysis from a paper in PLoS ONE suggests the lactase gene evolved in Europe because there isn't enough sunlight to produce the vitamin D needed to take in calcium—so milk drinking helped meet that deficiency. In Africa the lactase gene evolved in conjunction with early milk-producing domesticated animals—helping boost protein intake.
Milk. It does some bodies good. Especially with chocolate or cookies.