Most archaeologists now think that the homeland of the Indo-European languages was the steppes north of the Black Sea, and that the people who emerged from that region and spread across Eurasia were from the Yamnaya culture. Their remarkable success probably has to do with their mastery of horses, their use of wheeled wagons, and their resistance to Yersinia pestis, the organism that causes the Black Death.
But maybe their adoption of dairying was another factor:
The long-distance migrations of early Bronze Age pastoralists in the Eurasian steppe have captured widespread interest. But the factors behind their remarkable spread have been heavily debated by archaeologists. Now a new study in Nature provides clues regarding a critical component of the herders' lifestyle that was likely instrumental to their success: dairying. . . .
A new study led by researchers from the Max Planck Institute for the Science of Human History in Jena, Germany has revealed a critical clue and it might come as a surprise. It appears that the Bronze Age migrations coincided with a simple but important dietary shift -- the adoption of milk drinking.
The researchers drew on a humble but extraordinary source of information from the archaeological record -- they looked at ancient tartar (dental calculus) on the teeth of preserved skeletons. By carefully removing samples of the built-up calculus, and using advanced molecular methods to extract and then analyse the proteins still preserved within this resistant and protective material, the researchers were able to identify which ancient individuals likely drank milk, and which did not.
Their results surprised them. "The pattern was incredibly strong," observes study leader and palaeoproteomics specialist Dr. Shevan Wilkin, "The majority of pre-Bronze Age Eneolithic individuals we tested -- over 90% -- showed absolutely no evidence of consuming dairy. In contrast, a remarkable 94% of the Early Bronze Age individuals had clearly been milk drinkers."
The milk came from cows, sheep, and goats, and possibly also from horses, so they were not picky milk drinkers.