intricate nested pattern shown below arises from many different simple programs.

Ever since the original development of the theory of evolution, there has been a widespread belief that the general trend seen in the fossil record towards the formation of progressively more complicated types of organisms must somehow be related to an overall increase in optimality.

Needless to say, we do not know what a truly optimal organism would be like. But if optimality is associated with having as many offspring as possible, then very simple organisms such as viruses and protozoa already seem to do very well.

So why then do higher organisms exist at all? My guess is that it has almost nothing to do with optimality, and that instead it is essentially just a consequence of strings of random mutations that happened to add more and more features without introducing fatal flaws.

It is certainly not the case—as is often assumed—that natural selection somehow inevitably leads to organisms with progressively more elaborate structures and progressively larger numbers of parts.

For a start, some kinds of organisms have been subject to natural selection for more than a billion years, but have never ended up becoming much more complicated. And although there are situations where organisms do end up becoming more complicated, they also often become simpler.

A typical pattern—remarkably similar, as it happens, to what occurs in the history of technology—is that at some point in the fossil record some major new capability or feature is suddenly seen. At first there is then rapid expansion, with many new species trying out all sorts of possibilities that have been opened up. And usually some of these possibilities get quite ornate and elaborate. But after a while it becomes clear what makes sense and what does not. And typically things then get simpler again.

So what is the role of natural selection in all of this? My guess is that as in other situations, its main systematic contribution is to make things simpler, and that insofar as things do end up getting more complicated, this is almost always the result of essentially random

An example of a basic pattern that is produced in several variants by a wide range of simple programs.

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From Stephen Wolfram: A New Kind of Science [citation]