Biology was born in William Lawrence’s lectures in the 18-teens. Its topics and educational identity coalesced in the 1880s and 1890s. We like to say it became modern in the 1920s, not only because everything in that decade was Modern, but because the breakpoint is real: it’s when the perceived clash between Darwin’s and Mendel’s ideas was resolved. This post is about the dangers of what came later: thinking that this resolution was the same as “knowing all of biology” and considering the rest to be filling in the details.
I’m not being especially precise with the terminology, as I’m concerned here with the Synthesis sensu lato rather than its precise step by step development. You can call it the modern evolutionary synthesis, the Modern Synthesis, or as I typically do out of habit, the New Synthesis. I’m writing about how instead of a decent intellectual “let’s say it works this way and test it,” it became a genuine dogma. A century earlier they’d have called it a Natural Law, as that’s exactly how it was viewed, within which the terms natural selection, evolution, and Darwinism were treated as synonyms. When the construct’s cracks really started to show, by the late 1980s, people started using the term neo-Darwinism, or to put a little sting in it, “neodarwinism” without a capital.
There’s also a bit of sociocultural context involved:
The whole construct looks like this (here’s the PDF, for easier viewing). The basic model is purely reductive: intra-population genetic dynamics and population-level fitness outcomes are the engine, and all biological diversity, throughout time, is a straightforward cumulative outcome thereof.
I stress that none of this was idiotic, merely … well, intellectually overly certain, and professionally and pedagogically speaking, authoritarian. In fairness reality laid some cruel empirical traps for scientists to fall into. Certain high-penetrance genes practically begged to be poster children for “how genes work,” significantly the sickle cell phenomenon. You can see for yourself that it fits so nicely into all the above boxes (except speciation) that it practically nestles in. It was all too easy to think genes “for,” say, wings, or this or that kind of teeth or bird bill, would be just the same. And also in more fairness, there is one outstandingly important genetic subroutine for mammals which does correspond to one-genotype-one-trait, the major histocompatibility complex.
These concerns are historically tied to two disciplines’ steady renaissance in the 1970s and by the 1990s, dramatic re-entry into evolutionary theory: phylogenetic systematics (“family trees”) and developmental studies, producing in total what we now call Evo Devo. In a nutshell, that what you are, or can become, depends a lot on what you have been and just were.
All this is further historically tied to the resurrection of ethology in the 1970s and its refinement into behavioral ecology, which would eventually manage some degree of synthesis with cognitive research. That body of work provided tons of material to reassess old categories (“instinct”) and also to wrangle over what could or couldn’t be selected for.
This bit’s so important I need to highlight it.
And let’s not fail to get big:
In sum, without carping about the Hardy-Weinberg principle, and without disagreeing with anything about selection as such, lots of the extrapolations that followed the 1920s have been zapped.
Bluntly, different things happen at different scales, and quite a few of them are neither selection nor particularly facilitative toward selection. Some of them override it, or provide so much context for it that “selection” is itself an insufficient term for what’s going on. The neatness of the New Synthesis simply isn’t correct, and one doesn’t have to be un-Darwin or anti-Darwin or any other such canard to recognize it.
From here you can probably see why my own interests lie in genetic drift and speciation, as my previous posts Do the Drift, Where do little species come from?, and What are little species made of? indicate. It hasn’t been a good decade or two, though, not lately. The New Synthesis has shown itself to be culturally robust if not scientifically and enjoyed a bit more time too far past its sell-date. Several things are responsible: who’s died and who hasn’t, the concretizing effect of textbook contents, and a couple other things. Still, a man can blog.