CHAPTER THREE

A NEW MODEL FOR BIOLOGY

The logic of embryonic development

The discovery of genes that control embryonic development caused a true metamorphosis in biology, both from an experimental and from a theoretical point of view. On the experimental side, it made it possible to address problems that previously had seemed unapproachable. From a theoretical point of view, it inspired the conclusion that embryonic development is the execution of a genetic program (Gordon, 1999), in the sense that all processes of ontogenesis depend, more or less indirectly, on the transcription of genes.
Unfortunately, however, many have also concluded that the central problem of development, the problem of form, has been, in principle, resolved. Many details are still to be worked out, it is said, but the “logic” is now clear because the form of an organism depends on its genes.
In the book The Problems of Biology (1986), Maynard Smith has lucidly sounded a note of caution against this attitude: “It is popular nowadays to say that morphogenesis (that is the development of form) is programmed by the genes. I think that this statement, although in a sense true, is unhelpful. Unless we understand how the program works, the statement gives us a false impression that we understand something when we do not… One reason why we find it so hard to understand the development of form may be that we do not make machines that develop: often we understand biological phenomena only when we have invented machines with similar properties… and we do not make ‘embryo’ machines”.