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Friday, August 11, 2023

What is the Modern Synthesis?

Serious criticisms of evolutionary theory have been floating around for half a century. The main focus is over the Modern Synthesis and whether it's the best explanation of evolution. That requires a throrough understanding of what the Modern Synthesis actually means and how it's understood by most evolutionary biologists.

One view is that the Modern Synthesis is almost exclusively about natural selection. If that's true, then Stephen Jay Gould makes a good case when he argues that the Modern Synthesis is effectively dead—it was killed off by the neutral theory and the recognition that random genetic drift is a major player in evolution [Is the Modern Synthesis effectively dead?].

Another view is that the Modern Synthesis was expanded in the late 1960s in order to incorporate the new discoveries in molecular evolution so that the current version of the Modern Synthesis includes the neutral theory. Douglas Futuyma is one of several proponents of that view [Do we need a new theory of evolution?]. Here's how Futuyma explains it (ES = evolutionary synthesis),

Thus, evolutionary theory has undergone enormous expansion since the ES, with the neutral theory of molecular evolution its most radical extension [Evolutionary biology today and the call for an extended synthesis].

The latest kerfluffle comes from proponents of the Extended Evolutionary Synthesis (EES) who propose adding a raft of new concepts to evolutionary theory including plasticity, niche construction, epigenetic inheritance, development, etc. They appear to be coming from the ecological evolution side of the debate and their main concern is explaining the history of life. Thus, their version of evolutionary theory should contain all of the things that have an effect on the evolutionary trajectory of species over time.

This view is not the same as the version of evolutionary theory that explains how the frequencies of alleles change in a population. It's these competing views of what the Modern Synthesis is supposed to explain that causes much of the confusion, in addition to the fact that history of life researchers tend to have a very adaptationist perspective that doesn't pay much attention to genetic drift.

Epigenetics makes this discussion of evolutionary theory a lot more complicated because followers of the epigenetics cult want to overthrow the idea that changing allele frequencies is the definition of evolution. I was prompted to write this post by a paper that recently appeared in a Royal Society journal where three oceanographers proposed new algorithms that take into account the extended evolutionary synthesis with a focus on epigenetics (Epigenetic opportunities for evolutionary computation). Here's their description of the Modern Synthesis and a figure that explains how it relates to EES.

In evolutionary theory, the modern synthesis was developed throughout the first half of the twentieth century to combine the ideas of Darwin and Wallace’s evolution by natural selection, and Mendel’s principles of inheritance.

Note that random genetic drift is missing from their description of the Modern Synthesis and isn't included in the EES part of the Venn diagram. I don't think this is an accident. I think these authors have an all-to-common adaptationist view of evolution that focuses exclusively on natural selection. I think they completely missed the revolution that Futuyma and Gould refer to above.

It's interesting that their written description of the origin of the Modern Synthesis is very similar to the one that was in the Wikipedia article on Evolution. It seems to be a common view that the Modern Synthesis was simply natural selection combined with Mendel's laws. I've fixed the Wikipedia article by adding a reference to population genetics, which is much more complex and sophisticated than the simple laws that Mendel discovered. (The authors did include population genetics in their figure.) I also added the fact that population geneticists recognized the importance of genetic drift, mutation, and gene flow in 20th century evolutionary theory. In other words, scientists like Fisher, Haldane, and Wright knew that there was more to evolution that just Darwin and Wallace's natural selection.

Thank-you for reading this far. The question is; why don't scientists who write about evolutionary theory understand the history and the controversy over how to describe the Modern Synthesis? And how do articles like this get past peer review?


Joe Felsenstein said...

Note that this whole issue is what we should call The Modern Synthesis, not what contemporary evolutionary theory actually is. An issue of naming.

Larry Moran said...


It's a bit more complicated than that. As far as you and I are concerned, it's just a semantic issue. But for others, such as most EES proponents, it's a misunderstanding of modern evolutionary theory.

That's why dismissing it as simply an issue of naming can get you into trouble.

Donald Forsdyke said...

Building on the Cock-Forsdyke biography of the geneticist, William Bateson (2nd edition 2022), a preprint on this topic (April 2023) is available at the Social Sciences Research Network site (see SSRN "Forsdyke"). The title is "Speciation, natural selection and networks: three historians versus theoretical population geneticists." The three are the historians of science Mark B. Adams and William B. Provine, and scientist historian Donald R. Forsdyke.