How many paradigm shifts in the history of biology?

Dan Graur, in his usual interesting style, has raised the valid point that the « paradigm shift » terminology popularized by Thomas Kuhn has become way over-used. Every field seems to undergo several a year: Paradigm Shifting and Necrophiliac Fantasies about Thomas Kuhn.

Dan suggests as true paradigm shifters in biology: Mendel, Darwin, Kimura, and Hamilton.

In my opinion, Darwin is the one un-arguable paradigm shift in biology, on par with Newton or Einstein in physics or Lavoisier in chemistry. The questions which could be asked, the frame in which new results are to be understood, were completely changed.

My feeling is that Kimura and Hamilton worked within the Darwinian paradigm, and do not represent true paradigm shifts. They clarified important aspects, true, but they did not change fundamentally the way we look at the study of living organisms. By the way, if you are including these guys, surely Woese belongs in the same list?

For Mendel, I am divided. I would tend to put his work on the same level as Watson & Crick. It was super important work, but we already knew that heritability is important, that offspring look like their parents, and that there must be rules to find. Similarly, for Watson & Crick, we knew that there must be a molecular carrier of heritability.

A more important aspect of the avent of molecular biology as far as I am concerned, although I am not sure that it qualifies as a paradigm shift, is that biologists started thinking in terms of information content rather than in terms of biochemical content. The most important property of a messenger RNA is the genetic code which translates to proteins, not the amount of sugars in it.

And speaking of biochemistry, the only shift which in my mind can be comparable to Darwin’s little book is the rejection of vitalism. This in a way is what led to the question of the structure of DNA being relevant. If life obeys the laws of physics and chemistry, and can be explained by them, then each property of life, including heritability, must have a physical support with the right properties. But I don’t have a clean date and famous name, comparable to Darwin or Einstein (Wikipedia informs me that the synthesis of urea was not the magic bullet I was led to believe). And what is a paradigm shift without a famous old white guy?

So two paradigm shifts in biology for me, and only one with a clear before-and-after date. We do as well as physics as far as I can see. 🙂


Update: Dan’s post and this one spurred some discussion online.

Nicolas Le Novère has an interesting post defending as paradigm shifts changes such as the avent of molecular biology, or today systems biology. With a very nice analogy to population genetics, so at least go and look at his cool picture of Popper vs Kuhn.

Both Nicolas and Detlef Weigel have defended that Dan and myself have a too narrow view of what constitutes a paradigm shift. So I checked the Stanford Encyclopedia of Philosophy, and apparently it isn’t clear for anyone what exactly is a paradigm shift, and whether it’s relevant, especially in biology.

I also want to quote Rafael Najmanovich: « people confuse technological breakthroughs with paradigm shifts. » This fits a lot of molecular biology thinking in my experience.

All this has made me think a bit more about the question of whether Kimura’s neutral theory of molecular evolution is really a shift in its small corner of science, and the relation to other non adaptive theories. A blogging and twitter exchange which got me thinking; this made my day. 🙂

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