John Maynard Smith 1986, pp. 99–100)
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.
Maynard Smith’s point can also be expressed in another way: embryonic development is a process that increases the complexity of a living system in a convergent way, but we do not know how to build machines that produce a convergent increase of complexity. It must be added, however, that we do have an algorithm that describes how such a goal can be achieved. It is an algorithm developed for the reconstruction of two-dimensional images from one-dimensional projections, where it is known that a reconstruction is possible only if the projections contain as much information as the examined structure, a condition which implies that their number must not be inferior to a theoretical minimum (Barbieri 2003). A reconstruction from incomplete projections is equivalent to a convergent increase of complexity, and no algorithm can achieve it is a single step. It has been shown, however, that that goal can be achieved by a multi-step procedure, provided that (1) a number of ‘memory’ structures are built in parallel in order to store what takes place during the reconstruction, and (2) a number of codes are employed in order to transfer information from the memory space to the reconstruction space (Barbieri 2003). This model is in no way a description of what happens in embryonic development, and yet it gives us two important general concepts because it suggests that (1) there can be no convergent increase of complexity without memories, and (2) there can be no convergent increase of complexity without codes.
This amounts to saying that memories and codes are essential ingredients in any convergent increase of complexity, and this makes us understand why they are present in embryonic development.We have seen, for example, that the histone code creates molecular patterns that amount to biological memories and that the codes of the body plans are largely responsible for the three-dimensional structures of the embryos. What is emerging, in conclusion, is the idea that organic codes are key players in embryonic development but we still have a rudimentary knowledge of them and probably this is why we do not yet fully understand what goes on in a developing
embryo. The important point, at any rate, is that the organic codes show the way forward, like an Ariadne’s thread that allows us to navigate in the maze of complexity. Especially in the case of the most complex of all novelties created by embryonic development: the brain and the mind.