New Synthesis or Extended Synthesis?

Even some of those who accept that we need to move on from the Modern Synthesis think that it would be simpler just to extend it by incorporating new experimental observations and the mechanisms they identify. So, would an Extended (Modern) Synthesis be sufficient? To the Modern Synthesis, we could add all the other mechanisms (inheritance of acquired characteristics, symbiogenesis, lateral gene transfer, etc) and call that the Extended Modern Synthesis.

I understand the motives, but there are several reasons why I did not opt for that way of presenting the change.

First, it is a central and specific feature of Neo-darwinism to exclude the inheritance of acquired characteristics. The Modern Synthesis took Darwin’s Natural Selection idea and added to it:

(1) the Neo-darwinist (NOT Darwinist) view that Lamarckism was impossible,

(2) that inheritance was entirely through Mendelian genes, and

(3) that variation in DNA is random in the sense that it is not directed by any functional processes.

In brief, the Neo-darwinian mechanism is that variations arise by chance, natural selection then works to see which of those variations win the competition to reproduce and dominate the gene pool of later generations. These assumptions are so fundamental to the Neo-darwinist view that it would be a strange hybrid to add to it precisely those mechanisms that it sought to exclude. It is more honest to say ‘we got it wrong’ by excluding them.

The analogy would be with the way in which Newtonian mechanics was replaced by relativity theory. It would have been absurd to call relativity theory Neo-newtonism! When experimental observations show precisely those processes that the theory did not predict, then we should say so. Somehow that needs to be recognised. Just as the Neo-darwinists saw themselves as developing a new theory by integrating Mendelian genetics with natural selection, we now need in some way to recognise that nature is even more wondrous than they thought, and involves processes we thought were impossible. 

Second, it is important for historical reasons to recognise the injustices done to Lamarck, Waddington, McClintock, Margulis …….and many others. The dogmatic way in which Neo-darwinism was promulgated damaged reputations, it damaged careers, and it damaged whole disciplines which, like physiology, were excluded from contributing to the concepts of evolutionary biology. In my view, it even affected the reputation of Charles Darwin. Darwin was far from being a Neo-darwinist. He included the inheritance of acquired characteristics in his Origin of Species, even formulated his own mechanism (his theory of gemmules), and he acknowledged Lamarck in glowing terms: “this justly celebrated naturalist….who upholds the doctrine that all species, including man, are descended from other species.” (Preface to the 4th edition of The Origin of Species, 1866).

Third, there is the problem of nomenclature. Neo-darwinists, by using that term, captured the glow of Darwin’s name, but they do not always clearly distinguish whether they are talking about Darwinism or Neo-darwinism. This is the reason why criticisms of Neo-darwinism are often interpreted as criticism of Darwin. As Waddington knew well, it is perfectly possible to be a Darwinist without being a Neo-Darwinist. In the article I write:

“I start with some definitions. I will use the term ‘Modern Synthesis’ rather than ‘Neo-Darwinism’. Darwin was far from being a Neo-Darwinist (Dover, 2000; Midgley, 2010), so I think it would be better to drop his name for that idea. As Mayr (1964) points out, there are as many as 12 references to the inheritance of acquired characteristics in The Origin of Species (Darwin, 1859) and in the first edition he explicitly states ‘I am convinced that natural selection has been the main, but not the exclusive means of modification’, a statement he reiterated with increased force in the 1872, 6th edition.”

These considerations lead to the following conclusions:

1. It would be better to drop the name ‘Neo-darwinism’ in describing what replaces it.

2. The Modern Synthesis incorporates Neo-darwinism, which is why I incline towards dropping this name also. But, if we are to refer to an extended synthesis, Extended Modern Synthesis would be better than Extended Neo-darwinism since combining Neo-darwinism with Lamarckism would be a stark contradiction.

3. I prefer the term ‘Integrative Synthesis’ since it highlights the fact that it would be an integration of many mechanisms, each playing roles whose importance can vary at different stages of the evolutionary process, and each of which can interact with the others. This would be a genuinely systems biological view of evolution, emphasising those interactions.

What replaces the Modern Synthesis will necessarily be a hybrid incorporating different mechanisms. I suspect that the only common feature will be that evolution happened.

These points can also be explained using a development of a valuable diagram from Pigliucci and Müller. Click on the movie below

The movie shows the transformation from Piggliucci and Müller's figure to the one below:

Diagram developed from Pigliucci, M., and Müller, G. B. (2010) Evolution - The extended synthesis, MIT Press, Cambridge, Mass.

The central circle represents the main features of Darwinism. The left hand ellipse represents most of the additional features of neo-darwinism (modern synthesis). The right hand ellipse represents the proposed extension.

My view is that the extension can best be represented as an extension of Darwinism. Nearly everything added is compatible with the original Darwinist assumptions. The main exception is that genomic evolution includes lateral transfer which modifies the Darwinian ‘tree of life’ to become a ‘network of life’.

The difficulties with representing the extension as one of neo-darwinism is that there are several negative characteristics of neo-darwinism that are not specifically referred to but which make it difficult from a historical point of view to see neo-darwinisn as the base for the extension. As explained above, neo-darwinism explicitly excluded the inheritance of acquired characteristics, denied the role of processes of genome change other than by chance, excluded symbiogenesis, and embraced the central dogma. All these need to be abandoned. The coloured items in my version of the diagram indicate some of the features that are in direct contradiction to neo-darwinism.

Since writing this page in 2013 I have been able to check with one of the authors of the Extended Evolutionary Synthesis who confirms that they also see it as a replacement not as a simple extension of neo-Darwinism.