The lack of actual observation of humans having come from an "Unknown Common Ancestor" relating to bonobos, humans, gorillas, monkeys and look-alikes is truly the unknown. Now if someone wants to say similarity of DNA along with conjecture means evolution (obviously can't say it proves evolution) that's up to them. I no longer believe it, and for one reason in that, yes, there is no evidence that there was a "Common Ancestor," it is surmisal, and there is nothing to show that the missing or different DNA.
Clearly decisions about evolution are made by many, but as I continue reading and learning, I can see that it is based on, first the model (the theory of evolution), and then trying to fit what is considered evidence into the model. But it is assumption and imagination, based on what is considered evidence of the theory.