This is a question I've been wondering for a while, but no matter how much I search, I just can't find any relevant results. I'm hoping that the people of this community can provide some resources about this topic, or if nothing else some interesting conjecture or discussion.
The sort of specific inspiration behind this question was thinking about how autistic people are a source of very innovative language use, and are often more likely to acquire and never unlearn "wrong" forms of words or grammar. A handful of linguistic traits that I've seen pathologized in autistic people where I live are more or less accepted in the speech of some other speech communities around the world. So, given some people's beliefs on the role of autistic people in prehistory, could a historical speech community looking to adopt distinctive speech patterns, turn to its neurodiverse population for inspiration?
But I'm also curious about disabilities or disorders aside from autism. How have things like deafness/hearing impairment, blindness/visual impairment, facial paralysis or motor issues, dyslexia, intellectual disability, limb loss, and so forth, affected spoken language, written language, and signed language, as used by language communities as a whole? With regard to sign language, I've heard that the high rate of blindness among the Deaf community of Honduras' Bay Islands resulted in the development of a tactile form of the local village sign. I'm sure that given the rate of disability prior to modern medicine, probably especially among venerated elders, that some amount of language development in the world must have been motivated by accessibility in the same way as BISL — or at the very least caused by inaccessibility, i.e. mishearings or mispronunciations due to disability getting passed on to abled acquaintances.
So yeah. Even though most of the world has for a pretty long time now been pretty ableist, and this is reflected in many languages' vocabularies, I'm still wondering if there are any linguistic clues that our abled ancestors did in fact try to take good care of their disabled brethren. This is what the archaeological record seems to show, so how about the linguistic record?
That's a fascinating topic. I looked for some papers on the subject too, but sadly I couldn't find any; it's likely under-researched. So what I'm going to say is mostly conjectures.
I think that the historical impact is small, but growing.
As you said, most of the world has been quite ableist for a long time, and linguistic evolution is strongly tied to prestige - people emulate the language of the ones whom they want to identify themselves with.
So while it's theoretically possible that some historical speech community emulated the speech of its neurodiverse individuals, I don't think that it's likely, unless people with a specific neurodivergence were so common in that community that they had a big impact on its identity. For autism in special there's also the impact of the neurotype on information sharing.
And the process is mostly unconscious. Most of the time, people don't actively look for inspiration on that.
This is changing, however. Societies are becoming a bit more tolerant towards neurodivergence, and neurodivergent people now can actually interact with each other, and form their own subcommunities. That's why I think that the impact will grow.
The impact of neurodivergence on language and its evolution is quite different from, for example, blindness and deafness. The later are handled socially in a different way, but more importantly: they affect the medium through which you use language, while neurodivergence affects how you handle language internally. For example, blind people still use conversational maxims when communicating, while autists often have a really hard time with them (from what I've informally noticed they need to actively rationalise the neurotypical utterance in order to decode it).
How have things like deafness/hearing impairment, blindness/visual impairment, facial paralysis or motor issues, dyslexia, intellectual disability, limb loss, and so forth, affected spoken language, written language, and signed language, as used by language communities as a whole?
It's a rather small tidbit, but some people already noticed that [f], nowadays a fairly common speech segment, is often absent from the reconstruction of really old languages, such as Proto-Semitic and Proto-Indo-European; and it has also a tendency to debuccalise and become [h]. Both things are potentially related to tooth decay and loss, that were far more commonplace back then than now. I know that this is by no means on the same level as limb loss or facial paralysis, but it shows that those things could, indeed, have some impact.
There are also cases like the Nicaraguan Sign Language, that emerged from deaf children themselves communicating with each other.
I know that this doesn't address your main question directly, but I hope that it's still helpful.
while autists often have a really hard time with [conversational maxims] (from what I’ve informally noticed they need to actively rationalise the neurotypical utterance in order to decode it).
I have noticed this too, but it is something that's highly variable, like with anything on a spectrum. My brother and I are both autistic, but he struggles a lot more with conversational maxims than I do. It's to the point where half of his utterances are perfectly grammatical but also completely meaningless for anyone else, because his way of processing and using language just isn't supposed to be cooperative. I've heard people say that conversational maxims are socially determined, so for someone who generally doesn't follow social norms, it makes sense to understand and use language with different conversational maxims as well.
In some ways, my brother's way of speaking is comparable to Darmok from Star Trek, because it often relies primarily on a very rich set of allegories based on his interests, that he's the only person who actually knows how to decode. I swear that I read or heard somewhere about what this type of autistic speech is actually called, but I don't remember.
Anyways, there are some people who believe that without the social pressures of masking, that there would've been a lot more people who we'd now call neurodiverse, and that these would've also been more integrated into broader society, with specific roles best suited for their neurotypes. So if that were true, then I could see this group being "patient zero" for the spread of some sort of unconscious language change, and maybe even having some sort of prestige. Who knows, though.
Edit: Because I feel like this idea of "ancient autism" is sort of modern mythology, even though I want to believe it and don't think it's necessarily false.
