``If you consider all the biochemical steps required to get a message across a synapse, [...] you may wonder why such a complex communication system ever developed. The answer must be that this arrangement makes up for its complexity by allowing the nervous system to be flexible about the behavior it produces.''
Bryan Kolb & Ian Wishaw [KW01, p. 162]
The human evolution highlights the importance of flexibility mentioned by Kolb and Wishaw (see also the anthropological view in section 2.5). But what is evolution precisely? Evolution is a process that is applicable to biology, culture and even elementary particles. Unless stated otherwise, by evolution, we mean biological evolution theory2.5. While this disambiguation may seem unnecessary, evolutionary processes happen at various levels of scale, even in biology. For example, processes of learning encompass ``the long internal process which changes structural properties of its carrier system''[Wik07a]. Perhaps it is not so intuitive, but this is certainly applicable to development, learning and memory-formation in the brain. To avoid confusion with biological evolution in the regular sense, we will call these Darwinian processes. Calvin describes a Darwinian process as: ``A pattern (spatiotemporal firing pattern of a Hebbian cell-assembly, in this case) that copies with occasional variation, where populations of the variants compete for a limited work space, their relative success biased by a multi-faceted environment (both memorized and real-time, in this case), and with further variations centered on the more successful of the current generation (Darwin's inheritance principle).'' [Cal98] The brain allows patterns and ideas to compete across lateral connections. Multiple, perhaps conflicting or incomplete signals are often interpreted without much effort. We are wired to perceive and learn from our environment, to be able to adapt to it.

Evolution, or `descent with modification' [Cha01], is thought to consist of several elements [Cal04, Ch. 10]:

  1. A pattern or substrate
  2. The pattern, (or substrate in our terminology) is copied.
  3. Variations occur, typically from copying errors and recombinations. Some of this variance is heritable [Cha01].
  4. Variants compete with eachother for finite resources or space.
  5. Finally, the next round (generation) is centered around those variations that proved to be more successful (at reproducing, not just at surviving).

Element 3 is non-deterministic, or `random'. The final item is not. Furthermore, opening (biological) niches due, climate change, sexual recombination and temporary inbreeding (island populations) catalyze the evolutionary process [Cal98,Cal04, ch. 10].

Erik de Bruijn 2007-10-19