通过这个手段，我们认识到成人消化牛奶的能力其实是在近1万年内的进化成果 — — 而且还发生了多次进化 — — 并源自于那些懂得驯养绵羊，山羊和牛的文明。
From this approach, we have learned, for example, that the ability to digest milk as adults evolved within the last 10,000 years – and several times – in cultures that domesticated sheep, goats, or cattle.