This is a multi-part post in response to Merlin’s paper, “Evolutionary Chance Mutation: A Defense of the Modern Synthesis’ Consensus View”. See introduction and table of contents.
Merlin’s paper spends a lot of time dealing with the synthetic theory as defined by its original exponents – as well it should, since modern biology owes many of its intellectual underpinnings to these originators. Merlin described the writings of Fisher, Haldane, Simpson, Dobzhansky, and others as “canonical”, and deservedly so. They were the pioneers of how to marry genetics and Darwinism, and the fact that their work survived so well past the discovery of DNA is a testament to their intellectual power.
However, while these works should be deservedly referenced and pondered regarding what is and is not included in the synthetic theory, there are a few possibilities which should also be considered:
- Being fallible humans, not everything that they say will necessarily be consistent with their theory as described
- Being early pioneers, not all of their conceptions will be adequately thought out
- Again, being early pioneers, it was not clear which parts of the theory would be important to other disciplines, and useful for building knowledge
- Finally, just as “Darwinism” doesn’t refer to the theory as Darwin himself described it, the modern synthesis, having been formulated essentially two generations ago, has itself migrated a little from where it was originally conceived
- Many theories are organized around a core idea, and it is good to see whether it is the core idea being challenged or merely a peripheral theory.
Judging these requires looking to later literature as a guide to not only where the synthetic theory started, but also where it went and why it went there.
So, while Merlin viewed her job as defining what the original synthetic theorists meant, and then evaluating supposed neo-Lamarckian features of biology on those terms, I think a better set of goals would be to evaluate these features in comparison to the synthetic theory as currently described and used in the evolutionary sciences today. If Wright, Shapiro, Jablonka, and Lamb have indeed found something revolutionary, it matters little whether it would have been revolutionary to Simpson and Dobzhansky – it matters much more whether or not it is revolutionary in the context of the modern debate.
Having said that, I think that, for the most part, the definitions have not changed that much. One of the key tenets of the neo-Darwinian view of evolutionary change, both then and now, is that the needs of the organism do not affect the likelihood that a mutation is beneficial. According to neo-Darwinism, beneficial mutations are purely capricious – that is, there is nothing to guide a mutational process to a beneficial destination.
Why Are Haphazard Mutations Important to Neo-Darwinian Theory?
It is important to take a moment and reflect on why this tenet is important to the neo-Darwinian outlook of biology – an issue which Merlin does not directly address. Underlying the neo-Darwinian revolution is the desire to eradicate final causes from biology. Quoting Simpson, Ernst Mayr said that Darwin “has swept out such finalistic teleology by the front door”. In order to do this, Darwinists invoke natural selection as the sole driver of adaptive change. Therefore, if natural selection is in the driver seat, then the mutations themselves must not be more than accident. Otherwise, it would be the mutational mechanism (a mechanism internal to the organism itself), not natural selection, being the driving force of evolutionary change. Since the driver would be internal to the organism, this would leave a door for final causes to creep back into the study of biology. Therefore, neo-Darwinists are careful to keep that door shut as best they can.
So that is why mutational mechanism is important for Darwinists – if the mutational mechanism directs change in a certain direction, then natural selection is no longer the primary creative force in biology.
The Neo-Darwinian Influence Across Multiple Fields
This can be seen in the numerous theories that have been built off of neo-Darwinism. Modern phylogenic studies, for instance, build phylogenetic trees under the assumption that complex traits should only have arisen only once, since the ability for them to arise more than once by chance is nearly zero. This logic works only if the generation of the trait is accidental. If it instead driven by a mutational process geared towards that type of change, then this is no longer a valid criteria for selecting among potential phylogenies.
Likewise, molecular biologists look for evidence of positive selection in genomes by looking for gene sequences that diverge rapidly from a common ancestor. However, this is invalidated if the driver of beneficial mutations is actually the mutational process itself.
A good review of the use of chance in modern evolutionary biology is Gunther Eble’s On the Dual Nature of Chance in Evolutionary Biology and Paleobiology.
Why Subtle Shifts in Mutation Theory Can Be Revolutionary
It is unfortunate that Merlin didn’t go beyond the classic texts on synthetic theory precisely because then it would be clear why this question of the origin of mutations is revolutionary – it is revolutionary because so many fields and disciplines within evolutionary biology use the assumption of accidental mutations whose sole guide is natural selection as a foundation for their field. If this assumption is removed, then this would require the reorganization of many fields around new theoretical bases. It is this, much more than any congruence or incongruence with classic texts, which makes the overturning of the neo-Darwinian assumption about mutations revolutionary.
Since so many disparate pieces of the modern picture of biology are built on the neo-Darwinistic view of mutations, even subtle shifts in this view are likely to have a profound effect across all of biology.