“Similarity is the shadow of difference. Two things are similar by virtue of their difference from another, or different by virtue of one’s similarity to a third. So it is with individuals. A short man is different from a tall man, but two men seem similar if contrasted with a woman. So it is with species. A man and a woman may be very different, but by comparison with a chimpanzee, it is their similarities that strike the eye – the hairless skin, the upright stance, the prominent nose. A chimpanzee, in turn, is similar to a human being when contrasted with a dog: the face, the hands, the 32 teeth, and so on. And a dog is like a person to the extend that both are unlike a fish. Difference is the shadow of similarity.”
It articulates in a new way the old adage about lumpers & splitters, or hedgehogs & foxes, but then it adds what I’d call a postmodern spin: lumpers can’t be lumpers unless there are eras when splitters hold sway.