Every single one of us is an ape. One can't be a human if one isn't an ape. Therefore to claim that someone isn't an ape is to deny them their humanity. Actually it is saying they aren't even closely related to us.
Eh, at which point you demarcate between categories is pretty arbitrary unless you can show certain relations between those categories that emerge with the new demarcation that can be generalized in some useful (vague term here) way.
To me, what's an even more fascinating question is why can we understand language (and articulate, with visual/auditory symbols) but apes and other creatures can't. What is the mechanism that prevents them from doing so.
Maybe the core program of our mind, the primitive instincts that are in place before we are even born are ape like, but the moment a babe exits a womb it starts forming a theory of the world. Not only are humans different from apes, but to be human means to deny the very apelike program we have inherited.
From biological stand point of view we share some genes and they are our cousins, but we cant even mate with them. We have nothing in common with them even at the base level. The stona age man we come from is levels above an ape in terms of abilities.
The modern man is man of civilization and culture that has been amassed for millenia.
We have gone so far into human world that it no longer shares even simplest shred of ape like existance. The ape lives in embrace of jungle, but we have built the jungle for ourselves. We engineered and breed the civilization.
We no longer fit into the ape world. There can be no Tarzan. We no longer can share our space with apes. They cant fit into our world and the only connection we have with them is if we artificially create a bond between us and them. We can tame them and meet them at their level, because we can reduce our graceful world into theirs mental landscape, but they can never rise to our world. Not even remotely.
Apes are the closest thing we have in nature to ourselfs and no doupt they are intelligent, but no matter how intelligent they are they are nothing to us, but amusement and curiousity of scientific endeavour. Hell even the stone age people when confronted with missionaries that carry an ancient message the mental shock they are suffering is so great that many of them instantly go into deep depression and cry huddled in their huts confused and disgrunteled refusing to eat and live on completely ashamed of their sinful life.