Ernst Mayr and essentialism

Ernst Mayr was probably the greatest evolutionary theoretician of the 20th century, in my opinion. He had a grasp of the deep philosophical questions involved in the theory of evolution that went beyond any other biologist I have read. I am currently reading his wonderful book, One Long Arugment: Charles Darwin and the Genesis of Modern Evolutionary Thought. One of his most important contributions, I think, was his emphasis on the significance of the conceptual revolution introduced by Darwin, and in general his recognition of the importance of concepts in history of science (contrary to the positivists, the greatest scientific advances come not from the discovery of new facts, however important this may be, but through the introduction of new conceptual frameworks to encompass these known facts).

Mayr quotes Darwin (who, by the way, was also quite the theoretician, with a wide knowledge of philosophy): "About 30 years ago there was much talk that geologists ought to observe and not to theorize; and I well remember someone saying that at this rate a man might as well go into a gravel pit and count the pebbles and describe the colors. How odd it is that anyone should not see that all observation must be for or against some view if it is to be of any service."

Perhaps Darwin's greatest theoretical contribution was the mortal blow that he delivered to essentialist, or typological, thinking in biology, both across time (through the theory of evolution) and at any given time (through his emphasis on variation and natural selection as the mechanism for evolution). Evolution, which of course Darwin did not invent, postulates the transformation of one species into another. Darwin helped do away with any conception (and there were such conceptions) that this process of evolution occurred in spontaneous jumps from one species to another. The change from one species to another is gradual (and this is true regardless of what one makes of punctuated equilibrium), which undermines the idea of a hard and fast species. How can one say when a species ends and another begins? There are no sharp lines, and therefore one cannot speak of the essence of a species. A species is a dynamic, not a static, concept. "The sharp discontinuity between species that had so impressed John Ray, Carl Linnaeus, and others was now called into question by a continuity among species." (Mayr, pg. 20).

Perhaps even more significantly, the theory of natural selection has at its core the concept of variation. Within any given species, there is constant variation, with natural selection being "the preservation of favorable variations and the rejection of injurious variations" (Darwin). Mayr notes that essentialist thinking dominated western philosophical thought going back centuries, with the prototype being Plato's eide. By placing variation at the center of his theory (rather than variation as an imperfection, as a deviation from the ideal), Darwin further undermined the concept of absolute categories ("yes, yes, no, no and the devil take the rest!").

The species concept as developed by Darwin is truly a unity of difference. There is an objective reality to the concept of the species, which can be defined in a number of different ways, but often in terms of populations of organisms that can breed with each other and produce fertile offspring. However, within the species there is difference; and there is no ideal type to which members of the species can be measured. It is this unity of difference which is the foundation of evolutionary change, of movement.

An interesting question to explore is the relationship between essentialism and idealism. Basically, essentialism posits an absolute type, which has a greater reality than the individual representatives of this type, these representatives being only more or less perfect expressions of the type, of the ideal. Essentialism therefore places the word before the world ("In the beginning was the word"), the ideal or idea before and above matter. It is thus at its root an idealist philosophy. This is another way to look at the hostility of religious thinking (which is always in one way or another rooted in idealism) to evolutionary thinking, and in particular Darwinism.