So far archaeology and palaeontology, based on multi-variate analysis of skeletal features, have not found a new wave of immigration into the subcont… - Michael Witzel

None of the archaeologically identified post-Harappan cultures so far found, from Cemetery H, Sarai Kala III, the early Gandhara and Gomal Grave Cultures, does make a good fit for the culture of the speakers of Vedic […] At the present moment, we can only state that linguistic and textual studies confirm the presence of an outside, Indo-Aryan speaking element, whose language and spiritual culture has definitely been introduced, along with the horse and the spoked wheel chariot, via the BMAC area into northwestern South Asia. However, much of present-day Archaeology denies that. To put it in the words of Shaffer (1999:245) ‘A diffusion or migration of a culturally complex ‘Indo-Aryan’ people into South Asia is not described by the archaeological record’ […] [But] the importation of their spiritual and material culture must be explained. So far, clear archaeological evidence has just not been found"

I would not care, eg, if the IA-s could be shown to emerge from the proto-Masai culture of E-Africa.

apart from archaeology, our principal source for the early period must be. the Rigveda…