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
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)
