possibly Inner Asia. It was part of the diffusion of Indo-European languages from the proto-Indo-European homeland at the Pontic–Caspian steppe, a large area of grasslands in far Eastern Europe, which started in the 5th to 4th millennia BCE, and the Indo-European migrations out of the Eurasian Steppes, which started approximately in 2000 BCE. These Indo-Aryan speaking people were united by shared cultural norms and language, referred to as ārya, "noble". Diffusion of this culture and language took place by patron-client systems, which allowed for the absorption and acculturation of other groups into this culture, and explains the strong influence on other cultures with which it interacted. Fundamentals The Indo-Aryan migration theory is part of a larger theoretical framework. This framework explains the similarities between a wide range of contemporary and ancient languages. It combines linguistic, archaeological and anthropological research. This provides an overview of the development of Indo-European languages, and the spread of these Indo-European languages by migration and acculturation. Linguistics: relationships between languages The linguistic part traces the connections between the various Indo-European languages, and reconstructs the proto-Indo-European language. This is possible because the processes that change languages are not random, but follow strict patterns. Sound shifts, the changing of vowels and consonants, are especially important, although grammar (especially morphology) and the lexicon (vocabulary) may also be significant. Historical-comparative linguistics thus makes it possible to see great similarities between related languages which at first sight might seem very different. Various characteristics of the Indo-European languages argue against an Indian origin of these languages, and point to a steppe origin. Archaeology: migrations from the steppe Urheimat The archaeological part posits an "Urheimat" on the Pontic steppes, which developed after the introduction of cattle on the steppes around 5,200 BCE. This introduction marked the change from foragist to pastoralist cultures, and the development of a hierarchical social system with chieftains, patron-client systems, and the exchange of goods and gifts. The oldest nucleus may have been the Samara culture (late 6th and early 5th millennium BCE), at a bend in the Volga. A wider "horizon" developed, called the Kurgan culture by Marija Gimbutas in the 1950s. She included several cultures in this "Kurgan Culture", including the Samara culture and the Yamna culture, although the Yamna culture (36th–23rd centuries BCE), also called "Pit Grave Culture", may more aptly be called the "nucleus" of the proto-Indo-European language. From this area, which already included various