Donald Johanson

We are placed in the genus of Homo, which is Latin for man - Homo sapiens: supposedly wise men. I sometimes think - wonder - whether we really are wise men.

What makes us human depends on what place on our evolutionary path we're talking about. If you go back six million years ago, what makes us human is that we were walking upright. That's all. If you go to 2.6 million years ago, it's the fact that we're designing and making stone tools.

This was the most important discovery I had ever made in my life. It was a discovery which has irrevocably changed my whole life's direction. It immediately elevated me to the status of one of the world's leading anthropologists.

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.

But it really wasn't until three to four years later, when we had an opportunity in the lab to make very detailed observations, and comparisons with other fossil discoveries, that we realized she was a new species of human ancestor.

I realized immediately that this was a terribly important discovery, but I didn't realize how important it would be until we had spent a lot of time in the laboratory studying it.

But what really excited me was the idea that humans had a tremendous pre-history that went back millions of years. I wanted to go to Africa to find some of these creatures.

I find a tremendous receptivity among the public for the subject matter of, 'Where did we come from and how did we get here?' People are thirsty and hungry for information on our origins. I feel a responsibility as a major figure in the area... to convey to the public the knowledge of human origins in a way that is understandable to them.

I don't think we interbred with the Neanderthals at all. There are some people who think that there was some level of interbreeding. I think that we look so biologically different, that we looked and we acted so different, and we culturally were so different that we would not have had interbreeding between two species.

Scientists are very afraid of being proven wrong.

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.

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.