One has to devote oneself to a particular pursuit. To be successful at anything, you have to make a total commitment to it.

As an undergraduate, I had an opportunity to go on a number of archeological digs. So I had experience excavating, digging up remains of ancient Indian villages in the Midwest and in the Southwest.

When the first fossils began to be found in eastern Africa, in the late 1950s, I thought, what a wonderful marriage this was, biology and anthropology. I was around 16 years old when I made this particular choice of academic pursuit.

Normally, we are happy to find a fragment of jaw, a few isolated teeth, a bit of an arm, a bit of a skull. But to find associated body parts is extremely rare.

In our case, finding a Lucy is unique. No one will ever find another Lucy. You can't order one from a biological supply house. It's a unique discovery, a unique specimen.

I think that many of my ideas are correct, but I'll bet you, before my death other discoveries will be made that will prompt me to alter various ideas I have about human evolution.

The right question to ask from a Darwinian prospective is what was it about bipedalism that was so advantageous? Why did it lead to a - why did that adaptation ultimately lead to a species Homo sapiens that has come to dominate the planet today with six and a half billion people?