During the Early Bronze Age, populations of the western Eurasian steppe expanded across an immense area of northern Eurasia. Combined archaeological and genetic evidence supports widespread Early Bronze Age population movements out of the Pontic–Caspian steppe that resulted in gene flow across vast distances, linking populations of Yamnaya pastoralists in Scandinavia with pastoral populations (known as the Afanasievo) far to the east in the Altai Mountains^1,2 and Mongolia³. Although some models hold that this expansion was the outcome of a newly mobile pastoral economy characterized by horse traction, bulk wagon transport^4,5,6 and regular dietary dependence on meat and milk⁵, hard evidence for these economic features has not been found. Here we draw on proteomic analysis of dental calculus from individuals from the western Eurasian steppe to demonstrate a major transition in dairying at the start of the Bronze Age. The rapid onset of ubiquitous dairying at a point in time when steppe populations are known to have begun dispersing offers critical insight into a key catalyst of steppe mobility. The identification of horse milk proteins also indicates horse domestication by the Early Bronze Age, which provides support for its role in steppe dispersals. Our results point to a potential epicentre for horse domestication in the Pontic–Caspian steppe by the third millennium bc, and offer strong support for the notion that the novel exploitation of secondary animal products was a key driver of the expansions of Eurasian steppe pastoralists by the Early Bronze Age.

在青铜时代早期，欧亚草原西部的人口在欧亚大陆北部的广大地区扩张。综合考古和遗传证据支持青铜时代早期人口从本都-里海草原广泛迁移，导致基因跨越很远的距离流动，将斯堪的纳维亚半岛的颜那亚牧民种群与遥远东部的牧民种群（称为 Afanasievo）联系起来阿尔泰山^1,2和蒙古³。尽管一些模型认为这种扩张是新的流动牧区经济的结果，其特点是马牵引、散装货车运输^4、5、6以及对肉类和牛奶的日常饮食依赖⁵，尚未找到这些经济特征的确凿证据。在这里，我们利用欧亚草原西部个体牙结石的蛋白质组学分析来证明青铜时代开始时乳制品业的重大转变。在已知草原种群开始分散的时间点，无处不在的乳制品业迅速兴起，这提供了对草原流动性关键催化剂的重要见解。马奶蛋白的鉴定也表明了青铜时代早期马的驯化，这为其在草原传播中的作用提供了支持。我们的研究结果表明，到公元前三千年，本都-里海大草原可能成为驯马的中心，并强烈支持这样一种观点，即对次级动物产品的新型开发是青铜时代早期欧亚草原牧民扩张的关键驱动力。