Question is are... are organisms computable from their DNA? I gave this at a talk which... Heine... Heine Ursprung reminded me of, and in fact it was at a discussion in London of Developmental Society, in which I said that one day people will be able to compute a mouse from the DNA sequences alone which I'm told was the most outrageous statement that anybody had ever made at any Developmental Society meeting, and I actually left that in the discussion comment, that is there. And I think it is wrong because I should have added one extra thing. I should have added: computable from DNA sequences and some initial conditions — that I think I should have added to be absolutely correct. But in that sense, and of course I said that basically what we wanted to do to understand how you build... how a mouse is built, you want to build a mouse. Now, of course we might take over, as I said in that talk, the whole of southern England into a factory that would actually make mice, but I didn't mean it in that sense. I meant it in the sense that we would have it computable, we would understand the algorithm of how the mouse is built, because we could build it. And in fact I think that that becomes an essential... it's an essential argument, at least I think it's very essential to realise as to the nature of explanation in biology, right. We have many people who say, well, we want a theory of biology. We must have an explanation. So let's take something like limb development, which is a characteristic problem. What is the nature of the explanation for limb biology — Limb development — what is the theory of this? Now if you were a physicist, what you would want to do is to have a set of equations. These equations would... they would be called almost certainly the general appendage equation. It'd be GAE, this would be a large equation with a lot of constants in it, and if you plugged in various variables you could get wings with feathers, you could get feet with scales, and you could get legs with hair on them. That would be the physicists view. And of course in understanding this he would realise that it is the variables in this equation which determine this. And his picture would be, well, we know this is all programmed in the genes, so all the genes have to do is specify that K1 is this. Now, what might K1 be? K1 could be the diffusion constant of a small molecule, all right. K2, which is another one of the things in this equation, could be the distance over which it is moved or pumped. And another feature could be its chemical composition. And you would hope to put all of this in and of course since we don't have a continuity of limbs, we don't have wings with hair on them, and we don't have feet with feathers... I mean, our feet with feathers, our legs with feathers on them, we...the... this... this set of equations would then have certain eigenvalues and there would be forbidden areas in this which of course come from the nature of the interactions themselves. And a physicist would then say... well, he can understand it. Now there are some biologists who believe that that's actually the task we have to accomplish. They actually believe that, that wings are somehow... are solutions to some differential equation and that our task is to simply understand it in terms of this dynamical system and... and such biologists will couch their explanations in the following form. Now what I think the other approach has to be... it has to start with... with what is essentially the fundamental characteristic of organisms.