Humans began to rapidly accumulate technological knowledge 600k years ago

This was at least 200k years before the advent of speech if you go by the hyoid bone evidence.

I would consider this evidence that language predates human vocalizations. We already know deaf children will invent signs and gestures to communicate, and language not dependent on a hyoid bone. Do we have any way of dating the relevant neural structures through genetics?

What if the first language was a sort of sign language, and vocalizations were only auxiliary, optional? With time, humans who vocalized had a better chance to be understood, and their vocal tract evolved. Humans instinctively gesture to this day when speaking.

FOXP2 was thought to be the genetic basis for language, but this has been overturned[1]. As far as I know there isn't a good candidate for a gene selected for language.

[1] https://www.the-scientist.com/language-gene-dethroned-64608

This has been hypothesized, but the fact that there aren’t many or any purely sign languages still around and other primates don’t show signs of using signs makes that seem like a reach, IMO

I think we’d have trouble because we’d have to tie the gene to a specific linguistic cognitive function. My hypothesis is that humans configured themselves into self-replicating group structures I’d call institutions, and language evolved as a way to facilitate that. These institutions exhibit all the thermodynamic properties of life, and they have goal directed behavior independent of individual humans.

>other primates don’t show signs of using signs

other primates don't show signs of using vocal language either, yet humans have it

>there aren’t many or any purely sign languages still around

we're the only species of modern humans who survived, maybe Neanderthals/Denisovans etc. used sign language, who knows

maybe the fact that we started using vocal language made us much more superior evolutionarily speaking, making other similar species without developed vocal tracts extinct (by our warfare/assimilation)

deaf/mute people around the world have always historically come up with ways to talk using signs (different unrelated systems), i.e. we still have the means to do it, but it's unnecessary when you can produce sounds (freeing your hands to do work)

Yes these are the arguments in support of the idea. I’m not going to dismiss the idea completely but it’s not at the top of the list of likelihood imo