Helmut Humbach

"It must be emphasised that the process of polarisation of relations between the Ahuras and the DaEvas is already complete in the GAthAs, whereas, in the Rigveda, the reverse process of polarisation between the Devas and the Asuras, which does not begin before the later parts of the Rigveda, develops as it were before our very eyes, and is not completed until the later Vedic period. Thus, it is not at all likely that the origins of the polarisation are to be sought in the prehistorical, the Proto-Aryan period. More likely, ZarathuStra’s reform was the result of interdependent developments, when Irano-Indian contacts still persisted at the dawn of history. With their Ahura-DaEva ideology, the Mazdayasnians, guided by their prophet, deliberately dissociated themselves from the Deva-Asura concept which was being developed, or had been developed, in India, and probably also in the adjacent Iranian-speaking countries… All this suggests a synchrony between the later Vedic period and ZarathuStra’s reform in Iran."

"Iranianist H. Humbach, too, emphasises the same similarity pointing out the polarisation of relations between the Ahuras and the Daevas in the Gathic Avesta and the reverse polarisation between Devas and Asuras which only begins to occur in the later books of the RV; he concludes: “All this suggests a synchrony between the later Vedic period and Zarathustra’s reform in Iran” (1991:23)."