With the idea that what I wanted to understand was: how does the gene build an organism, development, and of course development of the nervous system? Because that was the most complicated of all the things. In fact when people said, 'Why don't… why do you want to work on the nervous system; why don't you choose something simpler first, like the big toe or something like that?' I said that I worked on the nervous system because it became absolutely clear from that that no simple hypothesis would account for what there is. Because there the great… at that time the great fear is that everything would finally be explicable by beta-galactosidase, by Jacob-Monod theories on… that there'd be a repressor, you take off the repressor, this thing would be induced and that's the way you get it. And what we wanted is to get to a problem which was so difficult that in fact it wouldn't be so easily explained. And the nervous system offered this possibility simply because everything… not only did you have to have cells, not only did you have to have cells in the right place, but they actually had to wire up together accurately. And it is the wiring problem of the nervous system, where things grow for very long distance and hook up at the end of the day, at the end of their journeys with the right cell target, that seemed that you would need very special explanations, for that could not be accounted for in simple terms, and therefore this is really what one wanted to know. Well, one of the discussions we had during this time was in fact whether we try and decompose this into a set of subsidiary problems and tackle each one. So there'll be problems of how cells move – that clearly happens in higher organisms, cells move around. There'd be problems of how cells grow, there'd be problems of the polarity of cells in the sense that cells go in one direction and not in another, grow in one direction, or face the world from one side of themselves and not the other. So how was all of this polarity established? And then of course there were whole questions of how you turned on all the different genes in a cell that distinguishes, let us say, a neurone from a liver cell. How did you, how did things get to be that? And so maybe differentiation could be studied, in… separately from development, taken out of the context of development and attacked in a… in a higher cell. And so I began to look around for examples which because of a favourable biological history of that species might show this in some exaggerated or isolated form. That has been something I've always done, because I think such is the diversity of, of living forms that you can always find a special case that aids you with your experiments. And there were classic examples of this; acetabularia – which is an alga – was so big you could actually suck out the contents of the cell and analyse them. And you felt certain you were looking at the same kind of process. So where could one find cases in which the exemplar would be such that it would show the same process – that is, it had to be essentially the same process that you found inside a living organism, and that enabled you to investigate it more readily.
