I’ve posted before about randomness and complexity. The montage above illustrates the distinction sometimes made between regular, complex, and random patterns. The text examples below provide another illustration:

Regular | Complex | Random |
---|---|---|

aaaaa aaaaa aaaaa aaaaa aaaaa aaaaa aaaaa aaaaa aaaaa aaaaa aaaaa aaaaa aaaaa aaaaa aaaaa aaaaa aaaaa aaaaa aaaaa aaaaa aaaaa aaaaa aaaaa aaaaa aaaaa aaaaa aaaaa aaaaa aaaaa aaaaa aaaaa aaaaa … | It was the best of times, it was the worst of times, it was the age of wisdom, it was the age of foolishness, it was the epoch of belief, it was the epoch of incredulity, it was the season of Light, it was the season of Darkness, it was the spring of hope, it was the winter of despair, … | BdhBt BMgkn YCbfR enFwJ DlMyq KFNoi rRdlu JwdTc IPoim oeFnQ gnhqq pqXon cIVVn rAOrx XtbcQ rZTBF sxeTi hLmBt gREOe Udrwt QHEMW OCBeV gQrHb gKbWa lklBL ivZMg JJrGa xVOZj QQBpb rfZWQ qRKTa ZEktK ofhTD UOXrm ZJAJs LPloV NhFjy … |

But how does one measure complexity? Grassberger notes that the widely-used Kolmogorov complexity is simply a measure of randomness. In other words, the use of Kolmogorov complexity implicitly assumes that complexity is just “randomness lite.”

There are three significant groups of people who doubt this. First, those complexity scientists who speak about the “edge of chaos” see the borderlands between regularity and randomness as being critically important, and in need of formal characterisation. However, rather than attempting to measure “complexity” in a way which would give both regular and random patterns low scores, this behavioural zone is now typically studied in terms of correlation length and other critical phenomena.

The second group are those critics of evolution who, believing *ex nihilo nihil fit*, assert that complexity has to come “from somewhere.” If complexity is just “randomness lite,” then random variation plus natural selection are sufficient to produce complex structures (indeed, *in silico*, the successes of genetic algorithms and genetic programming support that idea). Doubting this, these critics of evolution (such as Michael Behe) have suggested alternate definitions of complexity (irreducible complexity and specified complexity). However, since these alternate concepts have not been rigorously defined, they are not generally accepted outside the “intelligent design” community.

The third group, which includes figures such as Stuart Kauffman, also claim that random variation plus natural selection is inadequate to explain the evolution of biological complexity. However, they believe that the processes of self-organisation studied by the first group provide the missing explanation. This group does not use an agreed-upon formal definition of complexity, focussing primarily on simulation models in which non-trivial structures emerge. Their approach is interesting, but (as far as I can see) still vigorously debated.