"If you observed a human child using a stick to check the depths of a stream being crossed what would you think of his/her intelligence?"
I would wonder why his/her parents weren't watching him/her near the water.
And writing goes back much farther than a few hundred years.
Look, if you want to be an ape, that's fine. I prefer to be a human.
That doesn't answer the question. Is it a sign of high intelligence for a human child to, on her own, figure out that a stick will help her avoid the deep spots in the stream? Yes or no?
"And writing goes back much farther than a few hundred years.
In our culture yes. However many cultures did not develop writing as a method of storage until much later. An example is the northern plains aboriginals who passed on stories verbally and used other methods of communication than writing. Does that make them less than human?
"Look, if you want to be an ape, that's fine. I prefer to be a human.
You are an ape and a human, as am I.
False dichotomy.
You are a human, and an ape.
A relatively hairless, clever, tool-using ape. But an ape, nonetheless.