Much Ado About Randomness

randomness in evolution

I’ve seen some fuss being made about this new book, Bonner’s Randomness in Evolution. It’s fairly incomprehensible to me why it’s seen as controversial, although I can guess at why there is confusion, besides the back blurb stoking the fires by saying it “challenges a central tenet of evolutionary biology”, which it doesn’t. In fact, from what I read so far, I consider it an essential book for the layman interested in getting a comprehensive view of evolution.

The popular narrative of evolution, as taught in schools and retold by most science popularisers, emphasises the role of natural selection, a process that, while dependent on randomness and chance to work, effectively eliminates their influence by streamlining evolution along deterministic pathways.

As I emphasised in my lecture linked above, natural selection is not the default rule in evolution. It’s not the null hypothesis. It’s a working hypothesis that needs heaps of supporting evidence for every examined case. Treating evolution as a phenomenon primarily under the force of natural selection is a risky road that leads to adaptationism, the misguided and thoroughly debunked idea that seeks to explain every single character and trait as an adaptation to something.

This misconception of evolution being practically synonymous with natural selection is one that I try very hard to scrub off my students’ minds. Evolution is an entire framework, and natural selection is just one process within it. Its power can be great indeed, but it’s not always active, and it’s not always all-powerful.

But if natural selection isn’t the default force of evolution, what is? As I explained in this pretty old post, the majority of mutations (the raw data for evolution) are neutral, having no effect whatsoever (or, a negligible one at best). Therefore, the assumption of neutrality is the default one to make.

Mutations are random events, for our intents and purposes here (there are certain biases, but that’s getting into irrelevant technicalities). Most of them are neutral, and these neutral mutations will get passed on to the offspring, and may eventually get fixed in the population. This is what we call genetic drift, true “random evolution”. There’s no need to get into the complex mathematics of this (it’s probably the most sophisticated maths you get in all of evolutionary theory); suffice it to say that genetic drift is undoubtably the most important process when it comes to evolution at the molecular level, as is corroborated by evidence from wild populations. Most of the variation in DNA between species is attributable not to natural selection, but to simple genetic drift. In fact, genetic drift is powerful enough that, in some cases, harmful mutations can get fixed in a population through it.

Where the view stops being so clear is when we zoom out and start looking at macroevolutionary features – anatomies, morphologies, behaviours, traits that are commonly referred to as adaptations. Again, even for such features that directly affect reproduction and survival, natural selection must be demonstrated, not assumed. The reason is that, like at the molecular level, morphological characters are not all identical. A population of elephants do not all have the same trunk length. The variations, however slight, fluctuate and most likely have a neutral effect – just like most mutations. They will get passed on and maybe fixed at random, not necessarily being selected for.

The point I’m making is that in evolutionary biology, there is absolutely nothing controversial with saying that evolution has a significant random component. The book’s contents in this regard do not challenge anything, and the slight controversy about it is incomprehensible. In fact, I will be recommending this book for those infected by ultra-Darwinian thought. (“Ultra-Darwinians” are those who view natural selection as a single all-powerful force in evolution.)

There is one point where the book does raise controversy: the author advances the hypothesis that organism size affects the degree of neutrality. I will not comment on this since I’m still not through. I only wanted to address the silly kerfuffle made about “randomness”.

On a sidenote, I suspect one other factor at play is that many people approach evolution from an anti-creationist point of view, having learned evolution by memorising creationist debunkings, and are reacting to the word “random” because creationists will often say that all of evolution is random. Which it isn’t, because natural selection is still there, and it’s by definition a deterministic process.

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