The genetic adaptation of humans to the consumption of milk from dairying animals is one of the most emblematic cases of recent human evolution. While the phenotypic change under selection, lactase persistence (LP), is known, the evolutionary advantage conferred to persistent individuals remains obscure. One informative but underappreciated observation is that not all populations whose ancestors had access to milk genetically adapted to become lactase persistent. Indeed, Central Asian herders are mostly lactase nonpersistent, despite their significant dietary reliance on dairy products. Investigating the temporal dynamic of the −13.910:C>T Eurasian mutation associated with LP, we found that, after its emergence in Ukraine 5,960 before present (BP), the T allele spread between 4,000 BP and 3,500 BP throughout Eurasia, from Spain to Kazakhstan. The timing and geographical progression of the mutation coincides well with the migration of steppe populations across and outside of Europe. After 3,000 BP, the mutation strongly increased in frequency in Europe, but not in Asia. We propose that Central Asian herders have adapted to milk consumption culturally, by fermentation, and/or by colonic adaptation, rather than genetically. Given the possibility of a nongenetic adaptation to avoid intestinal symptoms when consuming dairy products, the puzzle then becomes this: why has LP been selected for at all?

人类对奶牛动物食用牛奶的遗传适应是最近人类进化的最具标志性的案例之一。虽然已知在选择下的表型变化，乳糖酶持久性（LP），但赋予持久性个体的进化优势仍然不明显。一种有益但未得到充分了解的观察结果是，并非所有祖先都获得了基因改造成持久性乳糖酶的牛奶。的确，尽管中亚牧民在饮食上对乳制品有很大的依赖，但他们大多数都是乳糖酶非持久性的。研究与LP相关的−13.910：C> T欧亚突变的时间动态，我们发现，在乌克兰出现5,960之前（BP）后，T等位基因分布在整个欧亚大陆（从西班牙到欧洲）的4,000 BP和3500 BP之间。哈萨克斯坦。突变的时间和地理进程与欧洲及其他地区的草原种群迁徙非常吻合。在3,000 BP之后，该突变在欧洲的频率大大增加，但在亚洲却没有。我们建议中亚牧民在文化上，通过发酵和/或通过结肠适应而不是在基因上适应牛奶消费。考虑到在食用乳制品时有可能通过非遗传适应来避免肠道症状，那么难题就变成了：为什么完全选择了LP？我们建议中亚牧民在文化上，通过发酵和/或通过结肠适应而不是在基因上适应牛奶消费。考虑到在食用乳制品时有可能通过非遗传适应来避免肠道症状，那么难题就变成了：为什么完全选择了LP？我们建议中亚牧民在文化上，通过发酵和/或通过结肠适应而不是在基因上适应牛奶消费。考虑到在食用乳制品时有可能通过非遗传适应来避免肠道症状，那么难题就变成了：为什么完全选择了LP？