There is sound evidence that chimpanzees and bonobos are more closely related to modern humans than they are to gorillas, and there is less sound, but still good, evidence that modern humans shared a common ancestor with chimpanzees and bonobos c.5-8 million years ago. So, there must have been at the minimum a sequence of ancestors and descendants providing a link between us and that common ancestor.

The task of reconstructing human evolutionary history is to recover and interpret fossil evidence that belongs to our (aka hominin) branch of the Tree of Life. Sorting out hominin fossil evidence from fossil evidence that belongs in adjacent closely related branches of the Tree of Life is a challenge. Even if you can do that, it is also challenging to sort ancestors from non-ancestral close relatives.

Some researchers stress how much we know about human evolutionary history. I will try and convince you that it is more helpful to err on the side of stressing how little we know.