Academic discourse in philology, ethnology, archaeology, paleontology, biology, and religion was plumbed in the eighteenth and nineteenth centuries t… - Jim G. Shaffer

[the demographic eastward shift of the Harappan population during the decline of their cities, i.e. an intra-Indian movement from Indus to Ganga,] “is the only archaeologically documented west-to-east movement of human populations in South Asia before the first half of the first millennium BC”, while the archaeological record shows “no significant discontinuities” for the period when the Aryan invasion should have made its mark.

It is currently possible to discern cultural continuities linking specific prehistoric social entities in South Asia into one cultural tradition. This is not to propose social isolation nor deny any outside cultural influence. Outside cultural influences did affect South Asian cultural development in later, especially historic, periods, but an identifiable cultural tradition has continued, an Indo-Gangetic Cultural Tradition linking social entities over a time period from the development of food production in the seventh millennium BC to the present.

Lacking fullest data, there is, nonetheless, a growing consensus that Harappan culture is the result of indigenous cultural developments, with no “Mesopotamian” people or diffusions of Western inventions, by whatever means, needed to explain it.