Throughout history there have been many other examples, similar to that of Haeckel, Huxley and the cell, where a key piece of a particular scientific puzzle was beyond the understanding of the age.

This fact immediately suggested a singular event - that at some time in the distant past the universe began expanding from an extremely small size. To many people this inference was loaded with overtones of a supernatural event - the creation, the beginning of the universe.

It was only about sixty years ago that the expansion of the universe was first observed.

Biology has progressed tremendously due to the model that Darwin put forth. But the black boxes Darwin accepted are now being opened, and our view of the world is again being shaken.

I entered Harvard in 1965 not really knowing what I wanted to do. This confusion seems to have lost me a fellowship. G. D. Searle and Company, the pharmaceutical firm, had their home office in Skokie, and they gave a fellowship each year to a graduate from my high school that was going to major in science in college.

What I actually wanted to do with my life is make a difference to the world. That led me into science very quickly.

Exercise helps me with stress. It changes your brain chemistry. I turn to Ashtanga yoga when I feel the need to relax. I love it, but it's not right for everybody. It's taught to you a little bit at a time, according to your body type and your strength. That keeps things challenging.

There are two things I enjoy most about my work. First, I get to work with interesting and enthusiastic people who are also fired up about science. Second, every once in a while I have moments in which I suddenly understand the solution to a problem that I've been working on - those are great moments.