Primatologist Frans de Waal has written books about morality in non-human animals. He and other scientists say humans inherited their moral values and social rules from earlier primate species. Given this, why did humans need religion to bolster morals and social cohesion?
Any stable human society need social Rules. Rules which are based on Values. And Values derive from Beliefs.
Therefore, I see no reason why the earlier ancestors of Homo sapiens idaltu would not have had some kind of Religion. They must have had some ! Indeed, Religion is an evolutionary adaptation : something natural.
Yes, religion is an evolutionary adaptation, but values and social rules derive from our animal ancestors, not from our beliefs. Beliefs are rationalizations for and manifestations of existing innate predispositions. Just like you said religion is a human construction, so are beliefs. They are cognitive creations, just like gods, which are another form of belief. Religion undoubtedly started much earlier than 85,000 years ago, but we don’t have any evidence for it yet. It’s difficult to imagine it existing over 1 million years ago, but if we find evidence, I’m all for it!
In most instances, humans did not invent it from scratch : they borrowed myths & stories, directly or indirectly, from other peoples.
You have a chicken and egg problem. Where did the first people get their myths and stories? Somebody invented it from scratch. Alternatively, myths and stories are just like beliefs, projections of the human psyche. With the evolution of our big brains and acquisition of language, we were able to construct representations of the human experience. Like you said, “humans gave to the Gods the attributes of the only kind they know : humans.” Myths are the stories of what people know — their own experiences transferred to external characters, often gods.