Well, it's only a stupid question if you know the answer! If horses are decended from an eohippus, where's the eohippus? If birds and reptiles are decended from dinosaurs, where are the dinosaurs? (I know - their brains were small and they died.) They probably all tasted like chicken, but in that case, why are there chickens left?

The tough question isn't why there are still monkeys, but why there are still humans!