Chaotic evolution: genes first, climate second?

by October 19, 2010

With the recent death of pioneering mathematician Benoit Mandelbrot — founder of fractal geometry and investigator of the associated idea that very simple formulae can produce very complex results — it seems uncannily coincidental that the New Scientist happened to publish a cover story on chaos theory and evolution (entitled “Fractal Life”) in the very same week.

The feature, by palaeoecologist Keith Bennett, strikingly argues that evolution is a chaotic system rather than a neat, Darwinian one driven entirely by natural selection. [Editor’s note: In case you suspect that SCOPE has Charles Darwin on the brain (see our recent post on the Darwin Correspondence Project), let me assure you that this post started as a notice on Mandelbrot, but ended up leading back to the naturalist instead.] Bennett points out that pollen samples and fossils demonstrate that species have typically not responded to long-run changes in the climate by evolutionary adaptation, but through shifts in both geographic distribution and abundance. Evolution, he contends, may be driven more by chaotic variations in a species’ genetic makeup than by external variables like climate.

I suggest that the true source of macroevolutionary change lies in the non-linear, or chaotic, dynamics of the relationship between genotype and phenotype – the actual organism and all its traits. The relationship is non-linear because phenotype, or set of observable characteristics, is determined by a complex interplay between an organism’s genes – tens of thousands of them, all influencing one another’s behaviour – and its environment.

Not only is the relationship non-linear, it also changes all the time. Mutations occur continually, without external influence, and can be passed on to the next generation. A change of a single base of an organism’s DNA might have no consequence, because that section of DNA still codes for the same amino acid. Alternatively, it might cause a significant change in the offspring’s physiology or morphology, or it might even be fatal. In other words, a single small change can have far-reaching and unpredictable effects – the hallmark of a non-linear system.

Read the rest.