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The basic mechanism seems to be that at different places and different times inside a developing animal different sections of its genetic program end up getting used—causing different kinds of growth to occur, and different structures to be produced.
But presumably the main thing that is going on—as mentioned above—is that at different places and different times different sections of the underlying genetic program are being used, and these different sections can lead to very different kinds of behavior.
For I tend to think that if pictures like the one on page 27 had ever in fact been seen in ancient times then science would have been led down a very different path from the one it actually took.
One aspect of the generation of randomness that we have noted several times in earlier chapters is that once significant randomness has been produced in a system, the overall properties of that system tend to become largely independent of the details of its initial conditions.
But as a practical matter, it is difficult to imagine that anyone in modern times would have the patience to generate many pictures of cellular automata by hand.
And instead what I expect is much like we have seen many times before in this book: that even though at the lowest level there is no direct correspondence between space and time, such a correspondence nevertheless emerges when one looks in the appropriate way at larger scales of the kind probed by practical experiments.
But now that the results of this chapter are known, one can go back and see quite a number of times in the past when they came at least somewhat close to being discovered.
And indeed the networks in pictures (g) through (i) on the previous page were specifically laid out so that successive rows of nodes going down the page would correspond, at least roughly, to events occurring at successively later times.
Defining the Notion of Randomness
Many times in this book I have said that the behavior of some system or another seems random.
starting with a single black cell and then applying a simple two-dimensional cellular automaton rule 250 times.