Must have been spoken language first. Early men didn’t live in solitude like the modern painters who avoided other people by staying in their art studio.
I agree that the spoken word (grunts, warnings and acknowledgments) between family/tribal members would have instinctive; but between other tribes - perhaps they used hand signals and/or drew ‘numbers/signs in the soil’ to illustrate topography, hunting and other food sources.
i.e. number of paces or sunrise/sunset - rivers, predators etc.,
IMHO prehistoric cave paintings were more likely a record or practical accounting function rather than ‘artistic aesthetics’.
I have always found it fascinating that the word for ‘mother’ is similar in all of the ancient languages.