The Synthesis?

Reading a bit of John Wilkins' blog this morning, I came across this quote from a recent paper by Michael Ghiselin (2001):

The notion that "the" Synthesis was somehow complete at one time or another in its history implies that the participants were aiming at some culminating event, like the Resurrection of Christ.The canonical texts are being treated as if they were The Gospel according to Saint Doby, The Gospel according to Saint Ernst, The Gospel according to Saint G. G., The Gospel according to Saint Julian, The Gospel according to Saint Bernhard, and The Gospel according to Saint Ledyard. Scientists are explorers, not prophets. For them to display themselves otherwise is as dishonest as it is misleading.

To that, Wilkins says, "Amen." Fair enough. So what was the so-called "Synthesis?"

The typical legend goes roughly like this. Starting around the 1920s and up to 1932, R. A. Fisher, J. B. S. Haldane, and Sewall Wright achieved a theoretical unification of Mendelian genetics and Darwinian natural selection. This achievement ushered in the field of theoretical population genetics, sometimes called the "modern synthetic theory." Against the background of the achievements of Fisher, Haldane, and Wright, the unification of biological disciplines, including systematics, botany, paleontology, and others was achieved by Theodosius Dobzhansky, Ernst Mayr, Bernhard Rensch, G. G. Simpson, G. Ledyard Stebbins, and others. The period ends around 1950. You can find pieces, variations, or elaborations on this story in Ernst Mayr and Will Provine's (1998), The Evolutionary Synthesis, Jean Gayon's (1998), Darwinism's Struggle for Survival, or Betty Smocovitis' (1996), Unifying Biology. There are other sources as well.

This standard story is a bit of a blunt instrument for sorting out all that happened (or didn't) during the associated period in biology. Indeed, it's mistaken to think that the unification of biology was achieved by 1950. And there are other ways of looking at these, roughly, three decades that are more helpful. Will Provine (1989), for instance, has argued that the period is better understood as one of "Evolutionary Constriction." Understood this way, we're not left with the impression that, in an event like the Birth of Venus, biology was unified. Rather, we're given the impression that there was a reduction in the allowable factors of evolutionary change in evolutionary explanations.

I'm sympathetic to Provine's view, although I'm tempted to soften it some. What the architects of population genetics achievement consisted in was, in Fisher's words, "a clearing of the ground of the debris of anti-Darwinian criticism" (Fisher [1932] 1983, pp. 289-290). That is, what Fisher, Haldane, and Wright managed to do was demonstrate how possibly, against the anti-Darwinians of the time, that natural selection alone could suffice to explain evolutionary change. And this isn't really a synthesis, or not a complete one anyway, since none of the three agreed even on the conditions under which natural selection could do what they claimed. Yet, Fisher, Haldane, and Wright lit the path of discovery that got, and still gets, huge amounts of traffic. This, then, is the softer view. Fisher, Haldane, and Wright set a point of departure from anti-Darwinian thinking no later than 1932 (the publication of Haldane's, The Causes of Evolution). Since then, the path has been and continues to be embellished.

References

Fisher, R. A. ([1932] 1983), "A Review of The Causes of Evolution", in J. H. Bennett (ed.) Natural Selection, Heredity, and Eugenics. Oxford: Oxford University Press.

Gayon, J. (1998), Darwinism's Struggle for Survival: Heredity and the Hypothesis of Natural Selection. Cambridge: Cambridge University Press.

Ghiselin, M. (2001), "Evolutionary synthesis from a cosmopolitan point of view: a commentary on the views of Reif, Junker and Hossfeld", Theory in Biosciences 120: 166-172.

Haldane, J. B. S. (1932), The Causes of Evolution. London: Longmans.

Mayr, E. and W. Provine (ed.) (1998), The Evolutionary Synthesis: Perspectives on the Unification of Biology. Cambridge: Harvard University Press.

Provine, W. B. (1989), "Founder Effects and Genetic Revolutions in Microevolution and Speciation: An Historical Perspective" in L. Giddings, K. Kaneshiro and W. W. Anderson (ed.), Genetics, Speciation, and the Founder Principle. New York: Oxford University Press, pp. 43–76.

Smocovitis, V. (1996), Unifying Biology: The Evolutionary Synthesis and Evolutionary Biology. Princeton: Princeton University Press.

Comments

[jay odenbaugh]

Rob,

First, kudos on what is a very interesting and rich blog. Second, you write the following:

"What the architects of population genetics achievement consisted in was, in Fisher's words, "a clearing of the ground of the debris of anti-Darwinian criticism" (Fisher [1932] 1983, pp. 289-290). That is, what Fisher, Haldane, and Wright managed to do was demonstrate how possibly, against the anti-Darwinians of the time, that natural selection alone could suffice to explain evolutionary change."

I find this view very attractive (especially more so than the unificationist line) but it raises a very general point about what the architects accomplished. Let me explain by way of example.

Anti-Darwinians largely agreed in the belief that natural selection was not a very powerful evolutionary "force". The alternatives - macromutations, orthogenesis, etc. - they were thought to be more efficacious.

Fisher for example responded by articulating a model where very small differences in fitness over generational time could take traits to fixation. So, the question "Is is possible for small differences in fitness to drive traits to fixation" is answered "yes". However, if i remember correctly, Fisher assumed the population size to be infinite (or effectively infinite). Given that idealization, why should the anti-Darwinians have been convinced by Fisher's argument? To my knowledge, this idealization was not relaxed at the time, so they could have denied that Fisher provided a how-possibly explanation.

At any rate, I may have the details wrong so it is just an open question...

jay

[Robert Skipper]

Jay,

Thanks heaps for reading. I enjoy the blog, even if I've not been posting much recently. The blog is especially rewarding when my colleages leave comments.... Now, you said:

However, if i remember correctly, Fisher assumed the population size to be infinite (or effectively infinite). Given that idealization, why should the anti-Darwinians have been convinced by Fisher's argument?

As I've looked more and more at Fisher, I think there's a good deal of legend surrounding his population size "assumption." The central question is why Fisher thought this assumption was reasonable. The answer in the air, and implicit in the received narratives, is that Fisher began thinking about the role of natural selection under the assumptions that populations were very large (for theoretical purposes, infinite). But I think that's incorrect.

I've begun a paper in which I treat Fisher's 1918 and 1922 papers and the 1930 book as one long argument (with some surrounding stuff). In doing so, precisely how Fisher justifies the population size assumption, among other assumptions, becomes pretty clear. It's clearest in Fisher's treatment of the Hagedoorn effect in 1922, in which he argues that the effect must be negligible since most populations (says Fisher) must be greater than 10^4 in size. The question then becomes whether we think that population size is too large for comfort --generally. And that's an empirical question.

At any rate, once Fisher lays out the parameters that depend on small population sizes, he sees then that he's able to assume, for mathematical purposes, that populations are infinitely large. No longer does size matter.

In response to your comment, the anti-Darwinians would have had to criticize Fisher's reasoning regarding mutation rates, the Hagedoorn effect, migration, and the lot before they could've gotten him for a bad assumption about population size. Fisher was much more careful than many of us have given him credit for being. And his arguments about these other parameters are pretty good. (And often too mathematically involved for his critics.)