Think of what Darwin first proposed. There are several key aspects.
- Common descent with modification (new traits)
- Inheritance of traits
- Natural selection favors some traits over others
The Modern Evolutionary Synthesis grew out of our later discoveries with genes mapping to traits and the effects of selection on populations & gene frequencies. Ernst Mayer, one of the players in the development of MES, wrote about some of this in his book, “The Growth of Biological Thought”. It’s a tough read but there are some gems in there.
Since that period, there have been additional discoveries and theoretical advancements made. One key area is Neutral Theory which describes how a lot of the observed variation is not subject to selection. This has impact on evolution in several ways. For example, it reveals how genomes can drift through variation and allow adaptive traits to emerge. I think this was a big extension to the body of theory.
Studies in the regulation of gene expression (and regulation of traits in general) have advanced understanding about the mechanisms available to organisms and how evolution has been facilitated. This added another layer of complexity to the systems we try to model but I wouldn’t say that these fundamentally fall into post-MES thought, compared to Neutral Theory… unless one includes Neutral Theory in the work. I think that applies to a lot of epigenetics as well. I generally see epigenetics as ‘yet another take’ on regulatory mechanisms. This is not meant to belittle the field, but to place ‘evo/dev’ and epigenetics in context. These are additional layers of regulation added to and interacting with other mechanisms previously discovered. So, not so much ‘revolutions’ but ‘step changes’ or ‘additions’. In fact, when we consider the effects of epigenetics as beneficial, adaptive traits, we come back to one of Darwin’s fundamental ideas: Natural selection favoring the retention of some traits over others.
I don’t see the core of Darwin’s theory being superseded with something significantly different. I think it’s likely that models and discoveries in the future will still come back to the basics of ‘descent with modification, some mode of inheritance of traits, and natural selection of traits’. A purely gene-centric view of evolution is gone at this point – though genes will always maintain a central role. Also gone is the idea that all the traits an organism displays are directly adaptive. So, many parts of what constituted the MES need to be extended with other mechanisms.
I suspect the next step in the game will be computer & information science modelling. That will be necessary because the math of biological regulatory networks and their responses require it. Unfortunately, what comes with massive simulation is often human incomprehensibility. Perhaps the discovery of some higher principles of organization and evolution will fall out of that work.