Thanks, I hadn't encountered that quote before, I'll add it to my collection.
If the subject matter baffles anyone, read and ponder the essay, You Are An Ape.
The point is that there isn't a single defining characteristic of the ape family that humans do not also possess. In a real taxonomic sense, we are *still* apes, just ones of the human variety. (Just as we are still primates, still mammals, and still vertebrates.)
Put another way, our differences from our ape "cousins" are ones of degree (in some cases large degree), but not of kind.