This is hard to explain, but easy to demonstrate.

We find it difficult to believe that all of these changes could occur more than once.

The reason we stood up is the million-dollar question in anthropology.

They don't all look alike. There are some very different shapes, with implications of how these fossils walked.

There may have been competition with other apes over resources in the shrinking forest.

It's hard to explain if you haven't been through it, but even when we were down, we just had the type of feeling that only we can have.