It's all very well saying that genes control development, but you know, that can't be possibly be true in a way. How do they make shapes? And... as you know, that's an enormously active field of research right now. I was fascinated by it between 1950 and 1960s, '65 or so, and I still am interested. I tried to approach it by a sort of quantitative genetics approach of taking morphological patterns in fruit flies and seeing how far I could change them by selection. Could I cause the fly to have different patterns of bristles on its head and that sort of thing. The notion at the back of my mind was that if you can answer the question, what changes can happen and what changes can't happen, by genetic selection, it may give you a clue to what the machinery is. I don't think it was a silly idea but I'm not convinced it really led anywhere very much. I mean, I think what's led somewhere is the identification of specific genes with specific effects on adult morphology, which, as you know, is very exciting at the moment. I guess - I think, really to push that approach to the direction it's been pushed in the last 20, 30 years, one needed molecular techniques that simply weren't available in the 1950s. So even if I'd thought of it, I probably couldn't have done it.

[Q] But you had things like the observation that certain groups of mammals produce horns and others don't, getting clues, I suppose.

Yes, there were clues around, but my feeling is that until one could do what one can do now, which is to not only identify genes but to sequence them, find out exactly in which tissue they first become active, find what happens if you knock them out, even find out what happens if you take them and transfer them into a different organism or a different tissue. When you can do all those things, you really can begin to sort of piece together a causal theory of ageing... of development.  We couldn't do any of those things in those days, we couldn't sequence genes, we couldn't move them around; all we could look at were the, sort of, the final results, the morphology. And although I was very devoted to the subject and thought about it a lot - well it's never a waste of time to think about something, but I'm not really sure that I got anywhere very much with it.