Actually it makes your earlier argument moot:
Since I never subscribed to the theory of evolution, I believe man's immediately-created intelligence allowed a written language to begin very rapidly
Both you and those who accept evolution agree that man had full and complete intelligence 6,000 years ago. So any concept of "gradual intelligence" is totally unrelated to the orgins of writing.
Based on your replies, I think you're either responding to the wrong person or have a real intellectual deficit.
Evolutionists claim man is millions of years old, and developed intellectual abilities only gradually. Creationists, which I agree with, claim man is roughly 6,000 years old and possessed high intellectual capabilities and reason from the very beginning of their creation.
On the subject of the first letter of the first alphabet, I believe the first 'letter' of an alphabet was created when the first man fashioned a symbol on a tree or the earth to warn his fellow tribesman of some local, inherent danger, and it became the accepted symbol to communicate danger amongst each other, in 'writing'. Or it occurred when he first carved a mark (symbol) on a tree to help him remember directions, or to warn other tribes not to trespass. One could even take origins of writing back to God Himself, who created the earth and hence created the 'tracks' of animals which symbolized they were present, told which species and how many, and explained where they were heading.
It's all very interesting and edifying to learn and speculate about this stuff, but it's even more interesting to watch the evolutionists and scientists' blood pressure rise as they toil and sweat to 'prove' their little theories and drive their agenda, rather than just present their findings and let the chips fall where they may.