Is evolution driven by mutation?

This post is a review of Masatoshi Nei‘s book Mutation-Driven Evolution (Oxford University Press, 2013); 256 pages, price £55/$89.95/€66.88.

As an undergrad student I spent countless hours at the University’s library. The “evolution” section was small, yet it contained the most important volumes, so I used to pick a random book every now and then and read it. That’s how I stumbled upon Nei’s book ‘Molecular Evolutionary Genetics’, and as I read its last chapter my life changed for good: I wanted to be an evolutionary geneticist! I have devoured ever since any book or paper by Nei. In 2008 I was doing a post-doc with Sudhir Kumar (a former Nei’s student). I remember once that Sudhir and I were talking about hypermutability and selection, and then Sudhir told me: “Nei is preparing a new book on mutation”. Since that day I’ve been patiently waiting until the book was ready. Now, five years after that conversation, the book is published. It was worth the wait.

neisbook

Masatoshi Nei’s book have a special place in my library

Nei’s ideas on mutationism were already sketched in his population genetics book published in 1975, and they were fully presented in a book chapter in 1983 and in his 1987 book I mentioned at the beginning of this post. He builds on the neutral theory, arguing that mutation and drift are more important than selection in molecular evolution. In this sense he continues Motoo Kimura‘s tradition. But Nei emphasizes the role of mutation over all, following the lead of Thomas Morgan and Hermann Muller. Indeed, the contribution of Morgan to evolutionary biology has only been recently acknowledge (as far as I know) by Nei, whilst other evolutionists (probably influenced by the biased account by Ernst Mayr) have completely ignored it.

‘Mutation-Driven Evolution’ is written as an historical account on how our knowledge about evolution has changed in the last 100 years. The first three chapters review the development of early evolutionary theories, with a strong focus on population genetic models (one of Nei’s fields of expertise). Chapters 4 and 5 account for the advent of molecular data and how it demonstrated that evolution is mutation-dependent. In chapters 6 and 7, Nei links the evolution of genomes with the evolution of phenotypic characters and speciation, a frequently missed aspect in many molecular evolution texts. Chapters 8 and 9 cover the role of mutation in adaptation and evolution. A last chapter summarizes the whole book and can be read as a stand-alone piece of text.

The book touches every aspect of evolutionary biology, and Nei gives his view on the cis/trans gene regulation debate, evolution of sex, the emergence of eusociality, Ohno‘s duplication model and Ohta’s nearly neutral theory, among other topics. He clearly states that mutation often produces adaptation, and much of the adaptation we believed to be the product of natural selection is not adaptation at all. In his words: “(adaptation) represents a human perception of the living status of the organism”.

If I have to say something negative about the book, I could only mention that Nei’s style is… well, Nei’s style. Somewhat opinionated and very critic with his opponents. Sometimes one gets the feeling that he is using modern arguments/evidences to attack postulates made by others some decades ago. Some may think this is unfair. Others (as I do) will understand that a point has to be made clear, sound and bold, and Nei has no problem in doing so.

The best way to describe what you’ll find in this book is to reproduce here the last couple of sentences:

“[…] mutation is the ultimate source of all biological innovations and the enormous amount of biodiversity in this world. In this view of evolution there is no need of considering teleological elements.”

Quod erat demonstrandum.

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3 Responses to “Is evolution driven by mutation?”

  1. Joel J. Adamson Says:

    (adaptation) represents a human perception of the living status of the organism

    I’ve been reading recently about how adaptation is the oldest aspect of evolutionary thinking. Most objections to the idea of evolution were phrased in terms of adaptation (because without you-know-who organisms would not be so well-adapted). And nowadays adaptation is the biggest objection to the idea that evolution is largely due to factors most people would consider “meaningless.”

    You say that Nei appears to be tackling statements made by scientists decades ago: many scientific discussion are defenses of statements made by scientists decades ago, so Nei is probably only responding to the unspoken level of discussion of most of the scientific community.

    The two go hand-in-hand: the Spandrels of San Marco largely fell on deaf ears, and only filled its detractors with resolve. I need to re-read that paper! Nei’s comment about adaptation as a human imposition is what many are afraid to say out loud, and it’s another aspect of science that is frequently accepted without evidence.

  2. Antonio Marco Says:

    Good point. I also need to re-read the Spandrels paper. I recently came across some comments by Elliot Sober and Michael Ruse about that paper, saying that most people have misread it. As I read it many years ago I probably misread it as well. Time to give it a second (thoughtful) read.

    The point is that there is a lot of discussion about adaptive versus non-adaptive evolution in the literature, but the possibility that adaptation itself is a human perception is overlooked. That may be more a philosophical question than a scientific one but still, looks very interesting.

    • Joel J. Adamson Says:

      Where I’m most uncomfortable is that adaptation is often taken for granted, without any evidence, just like the idea that organisms are machines. Applying a little more thinking to it, I think there are a few reasons to be doubtful of the idea of universal adaptation:

      1. Some organisms are better adapted to habitats that they don’t live in, for example kudzu that flourishes in the Southern United States, where it doesn’t have its usual diseases and herbivores.
      2. Superb adaptation to an environment is not required even for selection to lead to local adaptation. Slightly better is often good enough.
      3. Most biologists I know who consider adaptation to be the rule don’t think very often, or work with, genetic drift and mutation. They tend to have other philosophical predilections that would lead them in the direction of thinking of the world as law-like.
      4. At least in eukaryotes, the epistatic networks of existing genes are so strong that any change, even those that do get expressed phenotypically could be experienced as selectively neutral.

      Most of all, however, the idea that mutation and drift could lead to the diversity we see today just has been explored adequately, especially by people who study at the phenotypic level. That’s the most disconcerting. We could all be in for a big surprise 😀

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