Myths 2: The origin of species

So today, which is in the antipodes (we being so far ahead of you northern western types) the 200th birthday of an obscure British naturalist gentleman, we address this myth:

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

Here's some folk claiming just that:

One of the ironies of the history of biology is that Darwin did not really explain the origin of new species in The Origin of Species, because he didn’t know how to define a species. [Futuyma 1983: 152]

The Origin of Species, whose title and first paragraph imply that Darwin will have much to say about speciation. Yet his magnum opus remains largely silent on the “mystery of mysteries,” and the little it does say about this mystery is seen by most modern evolutionists as muddled or wrong. [Coyne and Orr 2004: 9]

It's balderdash. I sometimes wonder if the scientists who repeat these claims ever actually read Darwin. Darwin's book is a long argument against the fixity of species and for the evolution of species via the selection of varieties, which his publisher John Murray called "favoured races" in the subtitle he added to the book, for adaptive features that had as a side effect isolation from the ancestral forms.

There's a reason that such authors make this claim. It is modern dogma of those who think Ernst Mayr is the acme of evolutionary thinking that all speciation occurs through geographic isolation and local selection. This is referred to as "allopatric" speciation, literally speciation in "other fatherlands". The point is that selection for reproductive isolation cannot occur directly, because those that are able to hybridise with other variants are going to be fitter, and hence outcompete isolated forms; and interbreeding will swamp whatever population structure selection is acting upon (curiously, this is rather like the blending inheritance argument Fleeming Jenkin gave against natural selection working at all). But the point is not that the consensus view of a section of evolutionary biologists is that Darwin's mechanism, known today as "sympatric" speciation (i.e., speciation in the same fatherland), is not the cause of species. The point is that Darwin did think it was. So to say that he doesn't give an answer because it's the answer the authors do not like is plain silly.

Here's Darwin on the causes of species:

Again, it may be asked, how is it that varieties, which I have called incipient species, become ultimately converted into good and distinct species, which in most cases obviously differ from each other far more than do the varieties of the same species? How do those groups of species, which constitute what are called distinct genera, and which differ from each other more than do the species of the same genus, arise? All these results, as we shall more fully see in the next chapter, follow from the struggle for life. Owing to this struggle, variations, however slight and from whatever cause proceeding, if they be in any degree profitable to the individuals of a species, in their infinitely complex relations to other organic beings and to their physical conditions of life, will tend to the preservation of such individuals, and will generally be inherited by the offspring. The offspring, also, will thus have a better chance of surviving, for, of the many individuals of any species which are periodically born, but a small number can survive. I have called this principle, by which each slight variation, if useful, is preserved, by the term Natural Selection, in order to mark its relation to man’s power of selection. [Chapter III, p48f]

Does anyone doubt that Darwin held that selection causes varieties to become species? What is more, Darwin held that infertility was a side effect of adaptation to some, as we would now call it, adaptive niche:

In considering the probability of natural selection having come into action, in rendering species mutually sterile, the greatest difficulty will be found to lie in the existence of many graduated steps from slightly lessened fertility to absolute sterility. It may be admitted that it would profit an incipient species, if it were rendered in some slight degree sterile when crossed with its parent form or with some other variety; for thus fewer bastardised and deteriorated offspring would be produced to commingle their blood with the new species in process of formation. But he who will take the trouble to reflect on the steps by which this first degree of sterility could be increased through natural selection to that high degree which is common with so many species, and which is universal with species which have been differentiated to a generic or family rank, will find the subject extraordinarily complex. After mature reflection it seems to me that this could not have been effected through natural selection. Take the case of any two species which, when crossed, produce few and sterile offspring; now, what is there which could favour the survival of those individuals which happened to be endowed in a slightly higher degree with mutual infertility, and which thus approached by one small step towards absolute sterility? Yet an advance of this kind, if the theory of natural selection be brought to bear, must have incessantly occurred with many species, for a multitude are mutually quite barren. With sterile neuter insects we have reason to believe that modifications in their structure and fertility have been slowly accumulated by natural selection, from an advantage having been thus indirectly given to the community to which they belonged over other communities of the same species; but an individual animal not belonging to a social community, if rendered slightly sterile when crossed with some other variety, would not thus itself gain any advantage or indirectly give any advantage to the other individuals of the same variety, thus leading to their preservation. [p247]


More like this

When I read OTOOS in the 70s, I thought it was mistitled. Now we have the NY Times suggesting the same in…

an exerpt

"Charles Darwin called it the âmystery of mysteries,â a problem so significant and one he was so sure he had solved that he named his world-changing work after it: âOn the Origin of Species.â So he might be surprised to learn that 150 years after the publication of his book, the study of how species originate, a process known as speciation, is not only one of the fieldâs most active areas of study, but also one of its most contentious."

By David Renaud (not verified) on 12 Feb 2009 #permalink

Well done, John! I too tired of hearing this myth, particularly from evolutionary biologists.

I still think that in assessing the difference between what Darwin thought he had explained, and what he actually managed to explain, Coyne and Orr would be essential reading. To me, the assertion you call a "myth" looks like an assessment based on science and not a matter of personal preferences.

I don't see how Darwin's view differs from Fisher's (Genetical Theory of Natural Selection) or from Endler's (Geographic Variation, Speciation and Clines). Mayr's view is basically a rehash of Moritz Wagner's (Die Entstehung der Arten durch raumliche Sonderung). Darwin and Wagner communicated with each other about their differing views of speciation. I think the biggest problem is that population geneticist and systematists still don't talk to each other often enough.

By Michael Fugate (not verified) on 12 Feb 2009 #permalink

In Finnish tv-channel, some evolution biologists admitted that in dark barrooms most biologists admit that they have not read Origin of Species...or not read to the end. "oh dull/boring.." or smthing.
(I'm wondering that a bit, I found it interesting).

Let's be fair, the last chapters of Origin are also the ones that have aged the worst -- Problems With The Theory, etc. Yes, yes, Charlie, we know. Don't worry, you were basically right.

I find it's easy to get tripped up on terminology when you get into a close reading of Origin, because Darwin didn't have access to any standard terms. Some of the terms he did use are either opaque to speakers of modern English, or have different (fairly precise) meanings in modern biology. 150 years is quite a long time, after all.

Michael @5: I think that Wagner's ideas were likely the ones Darwin himself was consciously responding to, but as I have argued in a coauthored paper with Gareth Nelson I think that it is likely Darwin was also influenced by a book by an amateur anthropologist named Pierre Trémaux, from whom Wagner may also have gotten the idea. Mayr's influences probably included J. T. Gulick more than Wagner (Mayr mentions Gulick many times).

To those that would take issue with the works of Charles Darwin may I remind you that his scientific works have stood the test of time and now, about 150 years later, are accepted by open-minded, men and women trained in science who have looked closely at what he proposed. If still in doubt, please see some of the books and DVDs of Dr. Dawkins at Oxford Uniersity in England. On the other hand, the narrow-minded individuals who know by "faith" alone that the earth was created 6000 years ago, there was an Adam and Eve and Noah put all the animals in the world in his ark (sounds impossible to me). Why was there no mention of the diansaurs of over 65 million years ago? Rob Evans,B.Sc.,M.SC. Save us from the darkness of ignorance.

By Rob Evans (not verified) on 17 Feb 2009 #permalink

You know better than me on the historical details (I was remembering "Systematics and the Origin of Species"). My thoughts relate to my work on speciation; it seemed everyone had their pet theoretical model (and most often these were just rehashes of older models), but no one ever tried to test the predictions of the different models to see if they matched the patterns within and between species.

By Michael Fugate (not verified) on 18 Feb 2009 #permalink

My belief about speciation research is that two things are usually in play:

1. Everyone learns a mode of speciation from the group of organisms they are studying, form which they generalise.

2. Nobody does an overall study of the resultant models. Often, justifications are founded merely on mathematical models, which rely on the boundary conditions being instantiated. This is an empirical matter.

What we need is a massive study to see what happens. We also need conceptual clarity to avoid making vague or misleading claims. I tried to set that up in this paper:

Wilkins, John S. "The Dimensions, Modes and Definitions of Species and Speciation." Biology and Philosophy 22, no. 2 (2007): 247 - 66.

Hey, John! I beat you to this last year! See: Mallet, J. (2008). Mayr's view of Darwin: was Darwin wrong about speciation? Biological Journal of the Linnean Society 95: 3â16. See also . In the paper, I say:

We commonly read or hear that Charles Darwin successfully convinced the world about evolution and natural
selection, but did not answer the question posed by his most famous book, 'On the Origin of Species'.

and I conclude: ...

One might disagree with Darwinâs rejection of the idea of reproductive isolation as a definition of species, but one cannot say that he had not carefully weighed it up, before deciding against it. Darwin made a clear definition of species in his terms, while rejecting reproductive isolation as a definition, and then used this definition in his argument for speciation; in view of the diversity of views about species today, I do not think one can any longer fault him on this [back] in 1859.

As for empirical evidence for Darwin's view of species and speciation, as in your note above, see: Mallet, J. (2008). Hybridization, ecological races, and the nature of species: empirical evidence for the ease of speciation. Philosophical Transactions of the Royal Society B-Biological Sciences. 363: 2971â2986.