I overanalyzed and got 86%. It was pretty obvious which paintings were definitely done by human beings. Are we really not supposed to notice composition and design? If the idea was that they were all supposed to look random, I dissent. It was immediately clear that #3 and #6 were designed and not random splotches (look at the perspective in #6, and the way the black lines outline almost-human shapes. And in #3 there's an obvious pattern there). #4, too, is pretty orderly. Where I lost a few points was in presuming you were trying to be tricky, and take some more-or-less random-looking human paintings and pass them off as ape art. #2 is an ugly, sloppy mess and I knew right away it was the work of an ape. But I actually liked #1 and #5 - maybe it helps that they must have been painted on blue and black paper (whereas the other one was an ugly brown) and I assumed the backgrounds were painted as well. They did look pretty random, but I though perhaps they were random paintings by a person.
I have to say that though these quizzes are interesting your attitude is off-putting. I guess there are some art snobs out there who like to wave around their degrees and sniff at "plebians" but I tend to respond to works based on how they affect me. If your implication is that people are only pretending to respond to abstract art, I actually find that attitude more pretentious than that of the supposed snob's. How do you know what has an effect on me? How do you know what leads to a particular response? Why presume that just because you don't "get" something (and there's plenty I don't get too) the emperor has not clothes?
By the way, no person designed the Grand Canyon. It's still a pretty amazing sight.