About Rationally Speaking
Rationally Speaking is a blog maintained by Prof. Massimo Pigliucci, a philosopher at the City University of New York. The blog reflects the Enlightenment figure Marquis de Condorcet's idea of what a public intellectual (yes, we know, that's such a bad word) ought to be: someone who devotes himself to "the tracking down of prejudices in the hiding places where priests, the schools, the government, and all long-established institutions had gathered and protected them." You're welcome. Please notice that the contents of this blog can be reprinted under the standard Creative Commons license.
Thursday, June 29, 2006
Evolution, alive and well, thank you very much
The meeting was organized by the Society for the Study of Evolution, the American Society of Naturalists and the Society of Systematic Biologists, the three premier organizations of professional evolutionary biologists. This year the gathering featured an unprecedented number of participants (close to 1500) and of parallel sessions (11), as well as a whole day public symposium on those perennial troublemakers, intelligent design creationists.
The impression I got from attending several sessions on topics such as natural selection, adaptation, evolutionary ecology and the evolution of development is that the field is at the moment an interesting mix of what philosopher Thomas Kuhn called “normal” and “extraordinary” science. Normal science works within an established paradigm, such as the so-called “synthetic” theory of evolution – a series of theoretical constructs formulated in the 1930s and 40s to expand Darwin's original insight and reconcile it with population and quantitative genetics. Normal science is about “puzzle solving,” according to Kuhn, i.e. scientists spend their time not by testing the basic assumptions of their theoretical framework (because it is considered solid enough), but applying such framework to the elucidation of specific problems. For example, nobody at the evolution meetings this year presented a paper testing the existence of natural selection, yet plenty of researchers used the concept of natural selection to inform their empirical investigation of what is happening in populations of fish, amphibians, insects, plants and so forth.
Despite most talks at this year's evolution meetings being about “normal” science, there were also hints here and there that some major change may be on the horizon. A few researchers devoted their time to rather exotic-sounding evolutionary mechanisms, such as genetic assimilation and epigenetic inheritance. While this is not the place to get into a detailed discussion of technical issues, these mechanisms have the potential of significantly augmenting the theoretical arsenal of evolutionary biological theory, adding so far unsuspected sources of variation and complexity to our understanding of the biological world. Epigenetic inheritance, for instance, is a phenomenon by which non-genetic material (e.g., methyl groups attached to the DNA, used by the cell as switches to signal which genes to activate or keep silent) can be replicated and passed from one generation to another. The phenomenon has been suspected for decades, and solid empirical evidence in favor of its existence is now fast accumulating. We still don't know how widespread epigenetic inheritance is, and we don't have a detailed theoretical framework to include it into standard evolutionary theory, but one gets the feeling that once such requirements will be fulfilled, the current paradigm in the field will be significantly altered.
Do these new potential developments represent the possibility of what Kuhn called a “paradigm shift,” that is a dramatic change in the way we understand evolution? I doubt it. In fact, biology is a clear example of a science that has proceeded at least since 1859 (the year of the publication of Darwin's “Origin of Species”) without any such shift. The fundamental Darwinian insights that all life on earth share a common descent, and that natural selection is a major mechanism of diversification of biological forms, are still valid and at the core of evolutionary theory. Yes, much has been added by modern population genetics, molecular biology, paleontology, and developmental biology – both empirically and conceptually. But none of these additions have in any way undermined the foundations of the Darwinian edifice. This is different from what happened in geology before and after continental drift was recognized, or in physics when Newtonian mechanics was superseded by Einstenian relativity. In fact, the last paradigm shift in biology – ironically enough – occurred when Darwin convincingly rejected William Paley's arguments for intelligent design as an “explanation” of biological diversity. That is why the modern intelligent design movement promises not an advancement of science, but a regress to a previous, scientifically unproductive, paradigm.