groups and acculturation Michael Witzel refers to Ehret's model "which stresses the osmosis, or a 'billiard ball', or Mallory's Kulturkugel, effect of cultural transmission". According to Ehret, ethnicity and language can shift with relative ease in small societies, due to the cultural, economic and military choices made by the local population in question. The group bringing new traits may initially be small, contributing features that can be fewer in number than those of the already local culture. The emerging combined group may then initiate a recurrent, expansionist process of ethnic and language shift. Witzel notes that "arya/ārya does not mean a particular 'people' or even a particular 'racial' group but all those who had joined the tribes speaking Vedic Sanskrit and adhering to their cultural norms (such as ritual, poetry, etc.)." According to Witzel, "there must have been a long period of acculturation between the local population and the 'original' immigrants speaking Indo-Aryan." Witzel also notes that the speakers of Indo-Aryan and the local population must have been bilingual, speaking each other's languages and interacting with each other, before the Rg Veda was composed in the Punjab. Salmons: systematic changes in community structure Joseph Salmons notes that Anthony presents scarce concrete evidence or arguments. Salmons is critical about the notion of "prestige" as a central factor in the shift to Indo-European languages, referring to Milroy who notes that "prestige" is "a cover term for a variety of very distinct notions". Instead, Milroy offers "arguments built around network structure", though Salmons also notes that Anthony includes several of those arguments, "including political and technological advantages". According to Salmons, the best model is offered by Fishman, who Salmons himself argues that Genetics: ancient ancestry and multiple gene flows India has one of the most genetically diverse populations in the world, and the history of this genetic diversity is the topic of continued research and debate. The Indo-Aryan migrations form part of a complex genetical puzzle on the origin and spread of the various components of the Indian population, including various waves of admixture and language shift. The genetic impact of the Indo-Aryans may have been marginal, but this is not at odds with the cultural and linguistic influence, since language shift is possible without a change in genetics. Ancestral groups Common maternal ancestry states that "there is general agreement that Indian caste and tribal populations share a common late Pleistocene maternal ancestry