Linguistic studies indicate that human languages were not that different from modern languages 6000 and 7000 years ago. They had distinguishable sounds, vowels, consonants, syllables, roots and stems and so on.
Biology also indicates that mental abilities of humans changed little over at least the last 100000 years.
I wonder why no form of writing ever emerged before some 7000-9000 years ago, even logographic, symbolic, runic or any other kind?
I also wonder why the writing emerged nearly simultaniously in unrelated parts of the world (America, Africa, East Asia). Even if there was distance of some thousands of years between emergence of these writing systems, it still looks quite simultanious compared to the scale of some 100000-200000 years of the history of the modern human.
Why did no form of writing or symbolic expression appear independently in any part of the world, say 15-20 thousand years ago or so?