7 Complexity and biological evolution

7.2 Does complexity increase over evolution?

It seems almost certain that at some time in the past there were only organisms of (presumably) small biological analytic complexity while now there are complex beings which are difficult to understand (us). This does not mean, however, that complexity never decreases in any part of a species' evolutionary trajectory. In fact there is evidence that it does.*1

A very weak definition of complexity (such as size of genome) would be sufficient to explain an increase in the maximum complexity of all species under evolution. This is due to the fact that an incremental search for new ecological niches would necessitate this (albeit with a sharply decreasing rate of this increase over time as the space of new reachable niches increases without requiring a much larger genome). This would also imply a general increase in average complexity which would also tend to increase (by this explanation) increasingly slowly.

Figure 5: Incremental search over a space of possible genomes of increasing size

This is, however, a very weak notion of complexity increase. A stronger question is "Is there a general tendency for complexity to increase in each species over evolution?". I will not presume to answer this question, but only comment on some the suggested avenues of progress w.r.t. the types of complexity they refer to.

7.2.1 - Co-evolution
7.2.2 - Co-adaptation
7.2.3 - Inherent Self-organisation
7.2.4 - Meta-system transitions

What is Complexity? - The philosophy of complexity per se with application to some examples in evolution - 14 JUN 95

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