This is clearly written from an atheist's point of view. Feel free to disagree, but I would prefer to not devolve this into a discussion of religious people taking offense at my interpretation of what religion is.
Live and let live; believe and let believe. I'm as entitled to my belief as you are to yours.
The core reason for why religion exists is because people can assume and hypothesize.
Anyone with these skills can reasonably come up with a random (correct sounding) explanation and then based their actions off of that assumption (which is the basis for religion).
- This thing has happened. I did not do it. I have no idea why or how it happened.
- (Hypothesis) There could be someone else who did this for me. That would be a valid explanation.
- (Assumption) I can't find any other explanation, so there's probably someone who did this for me.
- (Religion) I really like the guy who did this for me. In return, I should be nice to him.
My thoughts are about some specific type of thinking in such a civilization: for example, if they saw a lightning for the first time, people would not think "Zeus is angry", rather they would be thinking "Wow, what could it be? I need to investigate this thing!".
You're sort of missing the point of where religion starts. A conclusion such as "Zeus is angry" already implies that this person considers many things as facts:
- There is a God names Zeus.
- He is capable of emotions.
- He takes his emotions out on us.
- There is no other source of lightning.
You say they're seeing lightning for the first time, yet they're already aware that Zeus is capable of controlling lightning? That's a contradiction. Either they know about it already, or they do not. It can't be both.
You're not starting from the basis of religion, you're describing what someone who is already religious will conclude. You're putting the cart before the horse.
Everyone (whether they're religious or not) who sees something for the first time, will wonder what that thing is, and where it comes from.
Assuming that it must be (a) God is a subsequent step. The reason for makign that assumption varies from person to person.
- A might immediately defer to God because it's clearly not manmade.
- B might ask around, understand that we cannot control it, and therefore defer to God.
- C might spend decades researching the event, unable to explain it (because they don't know what electricity is), and then eventually conclude that it must be metaphysical (thus deferring to God).
- D might think that it's not God. But when he sees E being hit by lightning seconds after E insulted D's wife; D will suddenly defer to God.
As a possible way of developing such a type of mind, I'm thinking about ancient times, when people were not yet Homo Sapiens. Probably they were living in a dangerous environment, where they need to solve some logical puzzles to survive. And so this type of thinking is evolutionarily developed and leaves no place for thoughts about any supernatural beings.
Even with the logical puzzles, a religion can be formed:
- Who put these puzzles there?
- Why did they put these puzzles there?
- We have the puzzles (and the puzzle maker) to thank for our intelligence!
Whether they end up worshipping the puzzles themselves (like the monkeys and the monolith), or the imagined puzzle maker; doesn't really matter. It's a religion either way.
There is a logical problem with religion, in that it accepts something that cannot be (or has not been) proven.
You cannot prove a negative, which means you cannot prove the absence of a god. Even if you exhaust all the empirical options, there's always the argument that "God does not want to show himself to us, and he is capable of doing so".
Even though religion will start from observed phenomena (which create an assumption of an omnipotent being, and then runs with that idea), an existing religion may be perpetuated based on assumptions that are never observed (such as the existence of a god).
When you think about it, the only real difference between science and religion is the level of certainty that is required to turn a hypothesis into a fact. Without sufficient corroboration, it's not a fact, but merely an assumption.
Science tries to not "jump the gun", and prefers to keep something as a hypothesis until they are certain that it's not just an assumption, but an actual fact.
- What kind of environment could this be?
I don't think this is related to the environment, but rather the cerebral abilities of the humans. Religion exists in the mind, not in the world. The assumption of the existence of a god is a mental phenomenon (which is triggered due to observing a random environmental phenomenon).
- How will this civilization progress? What will be the main differences in contrast to our current civilization?
If you rewrite human history by removing the ability to assume and hypothesize, then you are going to invariably hamper our civilization's evolution, most notably its technological advancement. Hypothesis is the foundation of the scientific approach, which leads to technological advancements.
Without the skill of hypothesis, that means that humans can only think about things that really exist.
This isn't all that far-fetched. I've seen studies that point out that 200 years ago, the average man was not able to consciously hypothesize.
The given example was asking two men (one born in 1990, one born in 1790) the same question: "If your stairs at home had 30 steps, how many steps would you take to climb it?"
- The 1990's man would think, calculate, and reply "30 steps" (or 15 if he's someone who takes large steps).
- The 1790's man, on average, would respond with "You're wrong. My staircase has 20 steps, and it takes me 20 steps to climb it."
And this is the crux of the issue. If humans cannot hypothesize, they can only deal with what's in front of them. That means that any discovered knowledge must have been pure luck.
Note that our real-world history contains many of these cases, where people stumble on a discovery (e.g. penicillin), rather than knowingly find out something they were actively researching.
If you take away the ability to hypothesize, all discoveries will be stumbled upon, no discoveries will be hypothesized.
As a simple example:
Columbus sailed West, because he believed that there would likely be a passage to India. Without hypothesizing, he would have had no reason to sail West. America would not be discovered until someone sailed West (for a concrete reason, e.g. fleeing from pursuing attackers, or e.g. being rendered unconscious and his boat floating West due to the current/wind).
1.1 Or, maybe, can you think of some other ways how such a civilization may appear?
Taking away these skills will dramatically change the world and our civilization's evolution. It will make the world unrecognizable to the viewer/reader.
So how about we paint a picture where we once had the skills, but no longer have them now?
- People were capable of hypothesis. They had religion and science. They built our civilization.
- We built our civilization up to a point where everything is either automated or well documented. No further technological research was deemed necessary.
- Humans lost the ability to hypothesize and reason. This could be due to many circumstances:
- You could create a villain plot, where a villain (disenfranchised by the horrors of religion) genetically changes humans and removes their skill of hypothesis. This could be unintentional; he thought he was removing the "religion gene", but instead ended up destroying the entire skill op hypothesis and assumption.
- It could also simply be a scientific experiment that got out and infected everyone, as seen in many, many zombie stories.
- Similar to how the people in Wall-E could no longer walk, humans may simply have unlearned the behavior over a long time period. If they haven't needed to make any discoveries for centuries/milennia, they will no longer be teaching their children these skills. While technically capable of hypothesis, no one has bothered to do so because there's no reason to do so anymore (everything is already taken care of, no problems need fixing anymore).
- Humans may be able to hypothesize, but their freedom is limited in a way that they're not allowed to do so anymore. There is an global autocratic government (that thinks of itself as a scientocracy but in reality is merely traditionalist and fascist). To a degree where dissent is nigh impossible (e.g. immediate execution when a "spy chip" in your brain alerts that you're hypothesizing).