Ernst Mayr on the importance of definitions

The Growth of Biological Thought

Image from Goodreads.

One of my pet topics is the concept of biological individuality, which I’ve written about quite a lot here. One question that comes up often, in fact what I initially asked Dr. Pepper when he used to carry on about it, is why does it matter?

So much ink has been spilled trying to define what an individual is, in the peer-reviewed literature of philosophy and of biology, as well as several books dedicated to the topic. What is the point of all this, to justify so much intellectual effort and so many dead trees?

A colleague has loaned me Ernst Mayr’s The Growth of Biological Thought, which tackles this question early on, not for individuality in particular but for the importance of definitions in general:

Scientific progress consists in the development of new concepts, like selection or biological species, and the repeated refinement of definitions by which these concepts are articulated. Particularly important is the occasional recognition that a more or less technical term, previously believed to characterize or designate a certain concept, was in reality used for a mixture of two or more concepts, like “isolation” for geographical and reproductive isolation, or “variety” (as used, for instance, by Darwin) for individuals and populations, or “teleological” for four different phenomena. –p. 43, emphasis added

The concept of an individual has, in fact, been repeatedly refined, and it has also been subdivided, with a whole slew of terms that refer to different subsets (“What kind of individual do you mean?“).

One further difficulty is posed by the fact that the same term may be used for different concepts in different sciences, or even disciplines of the same science. The term “evolution” meant something very different for embryologists from the eighteenth century (Bonnet) or for Louis Agassiz (1874) than it meant for the Darwinians; likewise, it meant something very different for most anthropologists (at least those directly or indirectly influenced by Herbert Spencer) than for selectionists. Many celebrated controversies in the history of science were caused almost completely because the opponents referred to very different concepts by the same term.

In the history of biology the phrasing of definitions has often proven rather difficult, and most definitions have been modified repeatedly. This is not surprising since definitions are temporary verbalizations of concepts, and concepts–particularly difficult concepts–are usually revised repeatedly as our knowledge and understanding grows. This is well illustrated by the definitions of such concepts as species, mutation, territory, gene, individual, adaptation, and fitness.–pp. 44-45, emphasis added

For example (though hardly a celebrated controversy), one critic of our latest paper insisted that what we had seen was not evolution, but it became clear that his definition of evolution was something different from ‘heritable change over time’ (exactly what his definition was I was never able to discern, and his comments are no longer available).

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