 And one of the hypotheses for years and years and years, and this is something that your listeners are probably familiar with, they've seen it on T-shirts and bumper stickers and coffee cups, is that the common ancestor we shared with chimpanzees would have been a knuckle walker, and that bipedalism evolved from something that was moving on its knuckles. And we can test this idea by looking at fossils that are from that time period, 6, 7, 8, 9, 10 million years ago. We don't have many.