Myths about Darwin

We are going to hear a lot about Darwin this year, especially this month for his birthday (happy 200th, Chas. You don’t look a day over 150) and in November for the sesquicentenary of the publication of On the Origin of Species. And you will hear or read repetitions of a number of common myths about Darwin’s ideas and theories. I thought, being a fecal disturber, that I would try to clarify one of these below the fold, in celebration of his birthday. I'll do the others when I can. If you can think of any more, let me know.

Myth 1: Darwin did not believe in the reality of species

Myth 2: Darwin did not explain the origin of species in The Origin of Species

Myth 3: Darwin was actually a Lamarckian

Myth 4: Darwin was a gradualist

Myth 5: Darwin thought evolution relied on accidents and chance

Myth 6: Darwin thought everything was due to natural selection

Myth 7: Darwin thought that Australian aborigines were closer to apes than to Europeans

Myth 8: Darwin was a social Darwinian

Myth 1: Darwin did not believe in the reality of species

It is a common claim that Darwin held that species are mere convenience. Mayr notes "one might get the impression [from the Origin of Species] that he considered species as something purely arbitrary and invented merely for the convenience of taxonomists" [Mayr 1982: 268]. Mayr goes on to note that he nevertheless treated species in a perfectly orthodox taxonomic manner and that he treated the concept purely typologically. In fact almost as soon as he died, this became the default view, based on the wording of the following passage from the Origin:

From these remarks it will be seen that I look at the term species as one arbitrarily given, for the sake of convenience, to a set of individuals closely resembling each other, and that it does not essentially differ from the term variety, which is given to less distinct and more fluctuating forms. The term variety, again, in comparison with mere individual differences, is also applied arbitrarily, for convenience' sake. [p42]

Many other passages seem to give the same impression, but it is false to say this. Throughout his work, Darwin held to a quite standard view of what species were, and it didn't involve interfertility, essences, or some other theoretical criterion for inclusion and exclusion. And what is more, he didn't change that view much before and after his evolutionary ideas. Indeed he wrote that he was not aware that evolution had changed his taxonomic work much.

Read the above passage carefully. Darwin is saying, as I understand him, the following things:

1. Species are individuals that resemble each other more closely than they do other groups. This is the standard view of species from antiquity - I call it the Generative View: A species is a group of organisms that are generated by their parents and which resemble them closely. This is not a conventionalist view in itself, nor is it an essentialist view. One might say it is rather more like Wittgenstein's "family resemblance" view, which we saw recently was inherent in Whewell's view of classification and pretty well every other taxonomist's and naturalist's as well. Here Darwin is not denying the reality of the groups themselves.

2. The conventionalism here is the rank of "species" and "variety". What Darwin needs to establish is that there is no qualitative difference between varieties within species and species themselves (because he will argue that varieties can evolve into species).

Darwin's rank conventionalism is not a denial of the reality of species, and elsewhere throughout his work and correspondence this is quite clear (see the relevant chapter of my book when it comes out). For example, this:

Before applying the principles arrived at in the last chapter to organic beings in a state of nature, we must briefly discuss whether these latter are subject to any variation. To treat this subject properly, a long catalogue of dry facts ought to be given; but these I shall reserve for a future work. Nor shall I here discuss the various definitions which have been given of the term species. No one definition has satisfied all naturalists; yet every naturalist knows vaguely what he means when he speaks of a species. Generally the term includes the unknown element of a distinct act of creation. The term "variety" is almost equally difficult to define; but here community of descent is almost universally implied, though it can rarely be proved. We have also what are called monstrosities; but they graduate into varieties. By a monstrosity I presume is meant some considerable deviation of structure, generally injurious, or not useful to the species. Some authors use the term "variation" in a technical sense, as implying a modification directly due to the physical conditions of life; and "variations" in this sense are supposed not to be inherited; but who can say that the dwarfed condition of shells in the brackish waters of the Baltic, or dwarfed plants on Alpine summits, or the thicker fur of an animal from far northwards, would not in some cases be inherited for at least a few generations? And in this case I presume that the form would be called a variety. [p33]

Darwin is setting things up a bit in a rhetorical fashion. Since he is arguing against fixists (rather than, as Richards 1992 has argued, the ideal morphologists or Naturphilosophen that he ought to have argued against - a much harder target) he suggests that the term species involves a notion of an "act of creation". This is true if you include the ideas of Cuvier and some fairly orthodox botanists in the English speaking world prior to around 1830. It is simply false if you think it reflects the professional views of natural history just prior to the Origin. But there's a separate interpretation: "act of creation" is not a religious claim, but a standard periphrasis for "initiating event" or "origin". If Darwin meant that, he is pretty right - every conception of species from antiquity to his day involved the idea that all members of a species were descended from some initial organisms. Creationists then as now thought these were the original two parents made by God, but there was a wide diversity of opinions, and few naturalists were creationists in the 1850s (Gosse being a rare exception, particularly with his Omphalos).

Darwin is trying to establish, as he does in the first two chapters of the Origin overall, that species have a lot of variation within them on which natural selection can act. This doesn't immediately mean that he thinks species are unreal - he thinks instead:

To sum up, I believe that species come to be tolerably well-defined objects, and do not at any one period present an inextricable chaos of varying and intermediate links [p137]

and gives reasons based on the heterogeneity of the effects of geography and natural selection.

So, why did people like Weismann, Muller, Haldane and others think that Darwin disbelieved in the reality of species? This view was reinforced around the end of the 19th century, especially in a debate published in The American Naturalist in 1908 (see refs), and it seemed to be very congenial to the nascent geneticists, especially in England. The notion became common currency amongst scientists and geneticists in particular over the next decades, culminating in a book by Guy Robson in 1928, The Species Problem, in which variation was taken to be an indication that species were not real things, influencing Dobzhansky and others in the "modern" synthesis.

So more on Darwin later...

References

"Discussion of the Species Question." The American Naturalist 42, no. 496 (1908): 272-81.

Arthur, J. C. "The Physiologic Aspect of the Species Question." The American Naturalist 42, no. 496 (1908): 243-48.

Bessey, Charles E. "The Taxonomic Aspect of the Species Question." The American Naturalist 42, no. 496 (1908): 218-24.

Bristol, C. L. "Otter Sheep." The American Naturalist 42, no. 496 (1908): 282.

Britton, Nathaniel Lord. "The Taxonomic Aspect of the Species Question." American Naturalist 42, no. 496 (1908): 225-42.

Clements, Frederic E. "An Ecologic View of the Species Conception. I. Past and Present Practise in Species-Making." The American Naturalist 42, no. 496 (1908): 253-64.

Cowles, H. C. "An Ecological Aspect of the Conception of Species." The American Naturalist 42, no. 496 (1908): 265-71.

Johnson, D. S. "Introduction: The Species Question." The American Naturalist 42, no. 496 (1908): 217.

Lewis, Frederic T. "Jordan on Fishes." The American Naturalist 42, no. 496 (1908): 286-88.

Macdougal, D. T. "The Physiological Aspect of a Species." The American Naturalist 42, no. 496 (1908): 249-52.

Richards, Robert John. The Meaning of Evolution: The Morphological Construction and Ideological Reconstruction of Darwin’s Theory, Science and Its Conceptual Foundations. Chicago: University of Chicago Press, 1992.

Robson, Guy Coburn. The Species Problem: An Introduction to the Study of Evolutionary Divergence in Natural Populations, Biological Monographs and Manuals; No. 8. Edinburgh: Oliver and Boyd, 1928.