"[…] tool use used to be considered uniquely human. And then when it was found in captivity by Köhler, this is in the 1920s, people would say, “Well, but at least in the wild they never do it.” And then it was found in the wild, and then they would say, “Well, at least they don’t make tools.” And then it was found that they actually also make tools. So tool use was one of those dividing lines. Mirror self-recognition is a key experiment that was first conducted on the apes. The language experiments, even though we now doubt what the apes do is actually what we would call “language,” they certainly put a dent in that whole claim that symbolic communication is uniquely human. My own studies on, let’s call it “politics,” and reconciliation behavior and pro-social behavior have put a dent in things. And so I think over the years every postulate of difference between humans and apes has been at least questioned, if not knocked over. As a result, we are now in a situation that most of the differences are considered gradual rather than qualitative."