I think we all know the role and importance religion has played in human societies. But when did mankind first begin to believe in God?
What does "God" mean? How is 'God' distinguished from gods? I'm assuming that 'God' means a Judeo-Christian-Islamic style monotheistic deity.
And who were the first people to believe in God? How did it happen and why? Was it a sudden epiphany? Was a burning bush or some other divine event involved? Where is the earliest evidence of a human belief in a godhead? What was or is the earliest human religion?
My impression is that most of the earliest cultures that we have information about were polytheist. The Sumerians, the ancient Chinese, the Egyptians. Perhaps even the early Hebrews, who seem to have emphasized their group loyalty to what appears to have been their tribal patron-god Yahweh, without necessarily denying that other alien gods existed as well. They might have only gradually decided that all other gods were evil, and finally, non-existent. Even relatively late, in early Christian times certainly, there was a widespread belief in demons, derived from the Greco-Roman daemons, minor deities, who the early Christians increasingly imagined as being evil and most emphatically not things to worship. So I'm inclined to say that the history of the West shows a rather gradual adoption of monotheism.
Then there's the 'anthropological' approach, based on evolutionary ideas and on the idea that surviving 'primitive' peoples were hold-overs from the stone age (which they certainly were in terms of their technologies). So the idea took root in the 19th century that (true or not) these cultures offered a window into the earlier stages of human life in paleolithic and early neolithic times. It seems that many/most of the world's 'indigenous' 'tribal' cultures were polytheist as well, and in many cases animist. They imagined themselves surrounded by supernatural power, which might in some cases be personalized as gods and withdrawn into the sky, but in other cases might manifest as supernatural power in seemingly mundane objects. There was great interest in the 19th century in tracing the 'evolution' of religion in a single line through various stages, from primitive to most advanced (usually identified with Christianity). Many theories proposing to do this were advanced.
But Christianity still had a strong influence on the 19th century, and more traditional Christian academics assumed that Adam and Eve were monotheists, as were Noah and his descendants. That suggested that polytheism was a later degeneration (as they saw it) of what had been an original monotheism. The myth of Babel is often cited here. (Muslims still believe this and believe that Islam is that original monotheism, reestablished.) So there was a variety of Christian anthropologist in the 19th century that set out to document the survival of this supposed primitive monotheism among tribal peoples. African tribes feature strongly in this work, in part because Belgian Catholics scoured the Congo for evidences, and in part because many African tribes do have myths of a single high god remotely distant in the sky, with many lesser gods and ancestral spirits beneath that are the objects of day to day religosity. Of course, this single high god isn't necessarily analogous to Judeo-Christian-Islamic monotheism and might instead be based on the idea of the tribe of gods having its own tribal chieftain just as human tribes do. But many of the Africans did seemingly attribute initial creation (often by procreation, as with a tribal ancestor) to that highest god, so these peoples could still be forceably crammed into the anthropologists' Biblical presuppositions.
The problem with the anthropological approach is that so much of the early work on this stuff was distorted by the presuppositions of anthropologists who were trying to acquire evidence for their own pet theories, that it's hard to know how much of their work can be taken at face value today.