At this point I became intrigued with what I still think is an unsolved but central problem of embryology development, which is: how in fact do you inherit these changes, you know? And here I had what I might call an impoverished but I think definitely tenable theory of morphogenesis which I called the morphoregulator theory. It was this: that cell adhesion molecules governed where their cells stuck together or whether they... when the molecules went away, they moved and we did know all these things happened. And so if you could find out how the genes for cell adhesion molecules were controlled in sequence, in terms of a loop of behavior, that might regulate how it happens. Let me make it very clear, I hope, by giving you an example.

The cells of the spinal cord... remember I said you have gastrulation, then you form something call the notochord, and then you have nerve cells that present themselves to make a spine... at the top of the spinal cord are a set of cells called neural crest cells – neural crest because they're at the top. What they do is they disassociate from the cord and migrate in definite pathways to form the peripheral nervous system – in fact some of the bones of your face – and they're very well-known, and they're in fact the source of melanin pigment, etc., in one branch. So what we found out was they were held together at the top of the spinal cord by this neural cell adhesion molecule, but the minute they were to migrate, the molecule disappeared from the cell surface, the genes were turned off, they'd migrate, go to a certain place, turn on this gene, put themselves back together again. Now obviously that doesn't explain the whole of shape. And since then it's been a brilliant set of efforts on the part of a variety of scientists to show that there are other kind of molecules that attract the cells in particular pathways, etc., etc. But I think the whole notion that the problem is to link the genetics with the mechanochemistry still remains as the central issue. And one of my colleagues here, Fred Jones, and I worked a long time on this and we showed that some very important set of genes that were determined by people working on fruit flies.