The best guess of science is that belief evolved as one of man’s first cognitive traits. Most likely it evolved with language, but that’s a guess. Until science is able to pin down the exact spots on the genome that control belief, which will never happen in our lifetime, all we have is speculation. What we know about language and belief says the two most likely evolved as complimentary traits and emerged very early in humans.
In our current age, we tend to think of belief as religion, specifically monotheism, like Christianity and Islam. It’s more accurate to think of religion as a subset of belief, which includes culture, altruism, faith in what others say and so on. There are lots of things we accept as a matter of faith that fall outside the supernatural. Belief is what allows acquired knowledge to be passed around and passed between generations.
Religion, like language, is an incredibly efficient storehouse of acquired knowledge. If you believe the tides operate on the digestive rhythms of the great invisible guppy beyond the horizon and you have jotted them down in the Book of Guppy, your people now have a very useful chart of the tides. It’s also easy to pass this knowledge from one generation to the next by teaching the great faith of the guppy to the children. The fact that there is no big invisible guppy is irrelevant.
The evidence we have suggests that the first religions were naturalistic. When you live off the land as hunter-gatherers, explaining the natural world is an important part of survival. The first “gods” were probably spirits associated with things early man observed in nature. The winds, the rains, thunder, lightning and the changing of the seasons would be things early humans would know and “explain” by associating them with the supernatural.
Fertility gods have been found in human settlements all over the world, which makes a lot of sense when you think about it. What makes life possible is the reproductive urge. Associating human fertility with animal and plant fertility, the fertility of the earth, is just another way of storing what has been learned about the natural world, including the people in it, into a portable set of beliefs that can be passed onto the next generation.
Most likely, religion became more structured and the gods more human, when man began to settle and develop agriculture. Human settlement requires cooperation and that means rules of conduct, enforcement of the rules, ways to deal with free loaders, how to defend property and so on. Religion makes for a very useful way to establish rules and enforce them. After all, if the gods say stealing is wrong, then punishing thieves is pleasing to the gods. Religion, it would seem, is essential to human settlement.
Something people often forget is that a big part of man’s environment is other men. Just as we have evolved to be a social animal, our cognitive toolkit evolved to benefit the social animal. It’s entirely possible that our sense of belief, our religious urge is what drove man to settle. Once man was able to accumulate enough knowledge about the natural world, settling down in one place may have been a natural development.
One of the great challenges of evolutionary biology is knowing which way the causal arrows point. More often than not, they point in both directions. The point here is that belief is one of the more important and powerful parts of the human animal. It lies at the core of what we are and how we went from foraging about in packs like chimps to living as we do today. It also shaped how we settled and how we altered our environment, which in turn helped shape humanity.
Modern people like to think we have abandoned all of those primitive things like gods, superstitions, rituals intended to change the direction of events. Christianity has mostly died out in Europe. About 70% of Czechs never attend church services. Only 44% of Germans say they believe there is a God. Churches in the Low Countries are being auctioned off as they no longer have parishioners. The main area of the Thirty Years War is no longer Christian. Imagine that.
It’s tempting to think humans are losing their religiosity, but that’s not how biology works. We can no more consciously abandon belief than we could will ourselves to be left handed Bolshevism, Marxism, Nazism and Fascism competed for a while to be the new religion of Europeans. Now it is multiculturalism and the nature cults like global warming and environmentalism. If the news is correct, the American cult of anti-racism is finding a home in Europe as well.
In the early years of wide spread narcotic trafficking, well organized gangs that operated under strict rules ran the trade. They were violent and chaotic, but the violence and chaos was manageable. Then the cops decided to chop the heads off the drug gangs, thinking the organizations would die or be great diminished. Instead, the bits and pieces of the shattered organizations became block-by-block street gangs, making war with one another over drug corners and sneakers.
The collapse of Christianity in the West has followed a similar pattern. The various national and regional expressions of Christianity provided order and rationality to human belief. The slow motion collapse of these organizations resulted in crackpot death cults like Nazism, Marxism and Bolshevism. Today we have various forms of nature worship and minoritism, which are just as nutty and self-destructive, just less bloody so far.
J. B. S Haldane identified fanaticism as one of the four important inventions, which he associated with the Judeo-Christian tradition. He was mistaken. The Greeks figured out that men would fight harder when they had a reason to fight. In all probability, fanaticism evolved not long after man had a reason to believe. Like belief, it is something that is a permanent feature of the human condition.
Humanity staggered along through the agrarian age with religions that helped make agrarian life sustainable. Christianity eventually allowed the West to advance beyond sustenance farming and finally became an asset in the rapid technological advance of the West. Whether or not the new religions will be an asset or the undoing of the West is impossible to know from where we sit. What we know is people will keep believing in something with some portion falling for it fanatically.