Where's the donkey to our horse? What I expected was that you'd give the nod to Brother Chimp. Then, I'd have to point out that a donkey is a lot more like a horse than Cheetah is to us. And there's that interesting matter of the *mules*.
I've always thought the most difficult problem of the evolutionists would be explaining why there isn't another species of human, similar to us in the same way that zebras are similar to horses. By rights, as complicated a mammal as we are, there ought to be a few in some out of the way places.
You don't naturally find zebras and horses in the same geographic area. There were, until recently (about 45,000 years ago, if I remember correctly), other species of hominids; at one point there were simultaneously fully-modern, or nearly so, humans in Africa, Neanderthals in Europe and the Middle East, and even a few surviving homo erectus in parts of Asia. Once homo sapiens began to spread out from Africa, the other species disappeared because they couldn't compete. (Neanderthals, who appear to have been very close to us in brainpower, hung around until quite recently.)