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]