I am one of these fortunate people who never looks back. Am I… I’m absolutely future directed and I never… when I make a decision, obviously at the moment when I made the decision all the evidence permitted… indicated I should make that particular decision, so I never question my past decisions. There's only one thing where I… if I had the opportunity to live my life over again where I probably would make a change. And that is that in the period from 1931, when I started at the American Museum [of Natural History], for the next 20 years I most conscientiously did what I was to… told to do at the American Museum: work out these… these bird collections which, after about eight or nine years, no longer really yielded new basic insights… biological insights to me, but, since it was my duty to work out these collections, I did this year after year. I think if I had shortened that period and had earlier begun to work on basic evolutionary theory on history of biology and particularly on the philosophy of biology, I could have achieved some things which now I will never be able to achieve because at age 93, one knows that one doesn't live forever.