But the human knee has a complex evolutionary history ... These bones can be present throughout the mammalian skeleton. This means some mammals may have sesamoid bones when even members of ...

There are important differences between the human skeleton and stride and that of ... difference is that chimps cannot extend their knees and lock their legs straight as humans can.

But this oversimplified view of human evolution is not quite right ... "It really showed us without a doubt that the skeleton was, like the knee, fully upright -- walking like we do," Johanson ...