Darwin in the Twenty-First Century: Nature, Humanity, and God (Studies in Science and the Humanities from the Reilly Center for Science, Technology, and Values) - Softcover

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Phillip R. Sloan is professor emeritus in the Program of Liberal Studies and the graduate Program in History and Philosophy of Science at the University of Notre Dame.

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Almost exactly fifty years before the Notre Dame conference, the world’s largest centenary commemoration of Darwin’s legacy was held at nearby University of Chicago. This event, organized by a committee spearheaded by University of Chicago anthropologist Sol Tax, drew nearly 2,500 registrants. In attendance were the primary leaders of evolutionary biology, paleontology, anthropology, and genetics, with a representation of sociologists, philosophers, and theologians (Smocovitis 1999). Two hundred and fifty delegates from universities and professional societies representing fourteen countries added an unusually high level of general academic prestige to the event as well.

Although other conferences were held in 1959, coordinated by an international super-committee formed in the mid-fifties―the Darwin Anniversary Committee―none equaled the University of Chicago symposium either in scope or in the assemblage of intellectual accomplishment. Accompanied by civic events, a grand procession to Rockefeller Chapel, and even an operetta written for the occasion, the Chicago celebration is an archetypal example of how scientific commemorations create, as well as celebrate, a major scientific consensus, in this case the theoretical framework of neo-Darwinism, often termed since a classic statement of Julian Huxley (Huxley 1942), as the “Modern Synthesis” or simply “Synthesis.”

The character of this neo-Darwinian theoretical framework, as it was highlighted at Chicago, was the outcome of a four-decade pro cess of theoretical unification of two conflicting strands emerging from Darwin’s original work, both of which could receive justification from the texts of Darwin and the arguments of his early interpreters. One was a theory of descent from common ancestors by means of natural selection, in which, as Darwin himself eventually came to explain the process (Darwin 1876), modifiable traits are transmitted from generation to generation by physical atomistic units―“gemmules” in Darwin’s original formulation. These were subsequently named “pan-genes” by Hugo DeVries in 1889, with the designator later shortened to “genes” by Wilhelm Johannsen in 1909. As it entered biological discourse, this “gene” concept was combined after 1900 with Men delism, particularly as interpreted after 1900 by Hugo DeVries and William Bateson. From this point it was combined with the chromosome theory by Thomas Hunt Morgan and his students through their landmark work on the fruit fly Drosophila (Schwartz 2008; Beurton, Falk, and Rheinberger 2000; Keller 2000).

The initial implication drawn by many from this theory of genetic inheritance for evolutionary change was that such change must be discontinuous, that normal genetic assortment processes in accord with Mendelian principles could only lead to recombinatorial novelty, and that only by means of discontinuous “mutations” of atomistic genes could genuinely new properties relevant to the evolution of species be introduced into a population. This strand deemphasized the role of natural selection in the genesis of new species. Into the 1930s, this theory, in modified form, had prominent supporters, even receiving endorsement in such influential works as Erwin Schrödinger’s 1944 What is Life? lectures (Bowler 1983, chap. 8; Schrödinger 1974, chap. 3).

The other strand emphasized evolutionary change as a continuous and gradualistic process, in which species are conceived as ephemeral entities that evolve slowly under the action of natural selection, often seen as a force operating directly on organisms. In conjunction with a sophisticated mathematical interpretation by the creators of modern statistics, most notably Karl Pearson, this interpretation placed itself in open opposition to the new Mendelism in the 1910s and ’20s, resulting in one of the great theoretical controversies within modern biology (Pence 2011; Gayon 1998; Olby 1987; Depew and Weber 1995, chaps. 8– 9; Provine 1971). Genetical determinism or statistical population analysis; saltational stepwise change or evolutionary gradualism; discontinuous mutations or the gradual accumulation of slight morphological changes in response to external selective pressure exerted by the environment―these were the oppositions that the Synthesis sought to reconcile.

Through the complex mathematical analysis of population genetics developed in papers of the 1910s and ’20s, and in detail in his major work of 1930, The Genetical Theory of Natural Selection, Ronald A. Fisher was able to deal with both sides of this controversy and successfully combine the statistical mathematics of large number populations with a theory of atomistic genes subject to micromutational modifications (Okasha 2012; Depew and Weber 1995, Provine 1971). Such small mutations, preserved within the population by Hardy-Weinberg equilibrium, could now form the raw material upon which natural selection operated. Natural selection was conceptualized as a deforming pressure analogous to a Newtonian force acting upon genes in populations rather than as an external selection process operating primarily on whole organisms in nature. The result of this mathematical theory of natural selection was a reworking of the traditional Darwinian theory of natural selection. It enabled one to maintain both a gradualistic theory of species change over time and the particulate theory of inheritance operating according to Mendelian principles. Random micromutations of discrete and atomistic genes formed the foundation of evolutionary novelty. Operating over sufficiently expansive time scales, this was deemed competent both to explain the microevolution of species accessible to field and laboratory observation, and also the longer-term macroevolution of major groups in geological time. The theoretical resolution of several of these issues that emerged in the 1930s and ’40s, associated with the names of Ronald A. Fisher, Julian Huxley, J. B. S. Haldane, Ernst Mayr, G. Ledyard Stebbins, Theodosius Dobzhansky, George Gaylord Simpson, and Sewall Wright, constituted “the Modern Synthesis.” The assumption that such a theoretical synthesis had been achieved, in which had been resolved the main historic issues surrounding Darwin’s theory of evolution by natural selection, formed the implicit framework of the proceedings of the 1959 Chicago symposium.

The 1959 Chicago commemoration provided a forum for all the main strands of development within the tacit consensus as it had coalesced to that point, with major papers by most of those typically identified as architects of the Synthesis: Ernst Mayr, George Gaylord Simpson, E. B. Ford, Alfred Emerson, G. Ledyard Stebbins, Sewall Wright, and Theodosius Dobzhansky. At the same time, there were indications of some of the tensions within the theoretical structure of neo-Darwinian theory that have emerged to greater prominence in the past half-century. These bear on the shape evolutionary theory may take in the next decades.

(Excerpted from Introduction)