program. But what if one looks not at a complete organism but instead just at some part of an organism?
Particularly on a microscopic scale, the forms one sees are often highly regular and quite simple, as in the pictures on the facing page. And when one looks at these, it seems perfectly reasonable to suppose that they are in effect produced by fairly simple programs.
But what about the much more complicated forms that one sees in biological systems? On the basis of traditional intuition one might assume that such forms could never be produced by simple programs. But from the discoveries in this book we now know that in fact it is possible to get remarkable complexity even from very simple programs.
So is this what actually happens in biological systems?
There is certainly no dramatic difference between the underlying types of cells or other elements that occur in complex biological forms and in the forms on the facing page. And from this one might begin to suspect that in the end the kinds of programs which generate all these forms are quite similar—and all potentially rather simple.
For even though the complete genetic program for an organism is long and complicated, the subprograms which govern individual aspects of an organism can still be simple—and there are now plenty of specific simple examples where this is known to be the case. But still one might assume that to get significant complexity would require something more. And indeed at first one might think that it would never really be possible to say much at all about complexity just by looking at parts of organisms.
But in fact, as it turns out, a rather large fraction of the most obvious examples of biological complexity seem to involve only surprisingly limited parts of the organisms. Elaborate pigmentation patterns, for instance, typically exist just on an outer skin, and are made up of only a few types of cells. And the vast majority of complicated