This heavily referenced book, Early Indians, by Tony Joseph, a recent collation of research into the origins of human life and civilisation in India, also has some interesting insights into the supplanting of ‘animistic’ or ‘shamanic’ philosophies by ‘religious’ substitutes.
Basically, recent archaeological research into pre-Harappan (pre-Indus Valley, or any other label, all fall short of describing the actual geographical spread of the civilisation of that period) townships shows that, for many thousands of years, these civilisations in India were organised on civil and pragmatic grounds. Meaning, there is no evidence of cities being constructed around central vistas of large temples or statues. What structures have been found, where it is possible that some kind of worship took place, are totemic.
Later civilisations appear to have actively destroyed much of this evidence, and replaced it with townships organised around temple structures.
Social organisation may therefore be inferred to have moved towards the concept of ‘gods’ from nature worship, and taken on a more central role.
This early period overlaps with the early Sumer civilisation, and the two almost certainly had much contact, in terms of trade. However, from the perspective of religion, their attitudes remained apart.
The point here is not to compare one civilisation with another, but to note that the move from wild agriculture to organised farming, that brought about a shift from primarily nomadic life, to the development of permanent towns, took different forms in different places.
Where the concept of gods dominated, it is reasonably obvious that a class of persons who associated themselves with the gods also took over control of commerce and civil structures, extracting taxes and subjugating all other occupations. Ultimately, they conferred legitimacy on the governors of those early groupings, whether it was hereditary or by tribal/community choice — hereditary eventually became the succession route of choice, as secondary sources, like the books of the Hebrew Bible, inform.
Therefore, it may not be correct to infer that the friezes and statues of very early civilisations always represent the gods of those people. It will be linked with the structures in which those carvings and representations are found, and the prominence of the location of those structures, vis-a-vis the layout and organisation of the township.