I'm not a linguist or linguistic anthropologist so I can't really address your question very well. This isn't a question for history, though, so I would suggest cross-posting this to /r/AskAnthropology. Even /r/askscience would be all right.

But basically I think your ideas on how languages--or religious--evolve are not really...right. While there certainly is room for conscious, intentional action in spreading religion at least (and language later in time) these things aren't really intentional acts; they are sort of a mix of passive change that happens slowly without people even noticing it, and intentional spread by people with an agenda to spread it. In the case of the first languages, it is almost certainly the former: language is a thing that evolved (and it required the evolution of both cognitive ability and vocal chords to even happen in the first place) and spread through the human communities that were around when it did evolve, and because it offered clear benefits the people who had a modern language ability were more likely to have children than the ones who didn't, and eventually it spread to everyone.

And this likely took place over many generations or perhaps even tens of thousands of years, with linguistic ability evolving slowly to the point where it is today (and probably has been for the last 50,000 years). And everyone today has the same ability to speak and to learn language, which suggests that it is something that evolved when human populations were still quite small, probably before modern Homo sapiens (i.e. us and everyone alive for the last 30,000 years or so) left Africa.

But beyond that very early language is hard to study. Neanderthals likely had some form of advanced language, though we don't know what it would have been like. Did Homo erectus have language? Neither would have had the same linguistic ability as us, but they probably had some form of language. And there does seem to be a sudden appearance of advanced art and other traditions that happens around 50-70,000 years ago and that has been interpreted as signs that we reached our current cognitive and linguistic abilities. There is also evidence of a population bottleneck with perhaps as few as 10,000 people alive that occurred around 70,000 years ago, and it would have been easy for something like language to spread throughout such a small community so that when populations began to climb again everyone had similar abilities.

But that's all just stuff I've picked up through the years of doing anthropology. Someone who is an expert in the field of evolutionary linguistics can surely be more useful. /r/AskAnthropology is a good place for that!