Does it, though?

I'm not religious myself (agnostic comes close-ish), but I would think, based on the evidence I'm aware of, that there must be an important function that spirituality and religion fulfill, especially to people not living in a 21st century first world society. After all, up until very, very, very recently, every group, society, people we today have any knowledge of, in every remote corner of the planet, had some sort of spiritual or religious framework. Atheism and a-spiritualism as a mass phenomenon is (to the best of my knowledge) a very recent phenomenon, and even most of the atheists I know have something that feels to me personally like a bit of a "replacement spirituality". If everyone's doing it, shouldn't there be a good reason for that?

Traces of such activity go back a long way in time, too. Use of ochre goes back almost 300 000 years, and while we don't know what they used it for then, later finds make a pretty solid case for it to be used in some spiritual context [1]. Neanderthals built structures that may very well have been connected to spirituality 176 000 years ago [2]. We have lots and lots of Venus figurines from the ice age Homo sapiens [3], we have lots of amazing cave paintings that may have been just naturalistic studies, but really don't look like it (like this 13 000 years-old chimeric guy: [4]). And then there are statuettes of lion-headed humans and lots of other art that doesn't appear to be naturalistic at all [5], probably right up to today, unless the very few uncontacted tribes are areligious exceptions or don't create spiritual art.

That sort of thing is costly. Effigies are costly, art is costly, rituals are costly, all the more so if you're living in an ice age environment that makes today's northern Siberia look kinda decent, or on a resource-starved island. Sacrifices are very costly, and they have been a part of lots and lots of cults and religions since time immemorial. There must be a reason why we kept doing this, and why people seem have such an enormous innate need for such things that they pick up such practices on their own again and again.

Actually, I'd say there must be some pretty huge upside to this, given that cataclysmic events and very hard times invariably deepen people's religiosity, despite all the selection pressure acting under a volcanic plume or in an icy summer or during devastating epidemics. They may shatter organized religions, but there are no atheists on a foundering ship in a storm, and all that.

That's not to say that our huge organized religions are a great thing, and should be kept as-is forever. Religiosity certainly has been and is being used as a means to deplorable ends. But there is, and probably always has been, another arguably much larger dimension to this, and people without churches probably wouldn't be steadfast atheists who never believe anything they haven't seen a peer-reviewed double-blind study on.

I'd speculate that if someone actually did that experiment and set some machine-reared Homo sapiens children loose on a pristine second Earth, and if by chance they'd actually make it through the first couple of generations, a complete lack of spirituality would probably be a disadvantage to them, and they'd probably fill that void before long. They'd have to hit the big existential questions at some point, after all, and if there is another way to answer them, I don't know it.

1: https://www.livescience.com/64138-ochre.html

2: https://www.nationalgeographic.com/science/article/neanderth...

3: https://en.wikipedia.org/wiki/Venus_figurine

4: https://en.wikipedia.org/wiki/The_Sorcerer_(cave_art)

5: https://en.wikipedia.org/wiki/List_of_Stone_Age_art