Thursday, 1 March 2018

Comparing the respective transmutation mechanisms of Patrick Matthew, Charles Darwin and Alfred Wallace

The original article has been published at the Biological Journal of the Linnean Society 123(4): 864-78 (2018): [This link should bring you to a guest entrance, that is, through the paywall to the full article. Otherwise try] A pre-print version is available here.

The elaborate acknowledgements
I'd like to take the chance to be more elaborate, here, than in the published paper. David Lloyd was a peer reviewer who waved anonymity. He and two anonymous reviewers helped to improve the paper a lot, especially on Alfred Wallace. A rant about the second reviewer (there were four in total) could follow, but everybody knows what "reviewer no. 2" means. I must praise the gumption of the editor in chief, John Allen, however. When I challenged the one glib and uncomprehending sentence that constituted the 2nd review, he bethought himself and revised his decision from rejection to re-write. Finally, thanks to Alexandra Elbakyan for literature.

[While the enigma of Matthew's education is only mentioned in the introductory paragraphs, a great amount of new information concerning it has been collected by a team (Anne Carroll, Julian Derry, Mike Weale, and I) and I have collated it in a blog piece lest I forget the links and details. In my opinion, this is a fine example of a person (Patrick Matthew from Newbigging—not Gourdiehill) that has for a long time rotten in the archives as a person of no historical significance whatsoever, brought back to life and linked to a question of historical significance.]

After a rash rejection by the Journal of the History of Biology, Mike Weale has, for some time, engaged in a ping-pong game of him commenting on the manuscript and me sending him corrected versions back. I also invited Julian Derry to become co-author around that time, but the plan never panned out for various reasons. Nevertheless, Julian's input via e-mail discussions was as helpful as that of Mike Weale.

The historical significance of Matthew's transmutation mechanism
Despite these important roles of Julian Derry and Mike Weale, the three of us reconstruct Matthew's views differently. (Reconstruction is inevitable for a record as incomplete as Matthew's. It's as if we have a most complete fossil record for Darwin, most of it for Wallace, but only a jaw, and a leg, and a tail for Matthew.) Let me sketch the differences between Weale, Derry and me as aptly as possible. Weale believes that Matthew proposed an early version of species transmutation through natural selection. Derry and I disagree.
    I think Matthew's scheme proposed species transmutation with natural selection also being in it, but not as central as in Darwin's mature theory. On the contrary, Matthew's scheme suggests that natural selection works species fixing except after catastrophes have ripped remnant species apart and thrown them into habitats which they did not naturally occupy before the catastrophe. That is, natural selection only ever works (anagenetically) to adapt a lineage to its environment and the catastrophe does the lineage splitting. Natural selection does play some role, here, during the process of species transformation and lineage splitting.
    In Darwin's mature theory, natural selection and the principle of divergence were sufficient to effect divergence and speciation in symparty. Darwin (1859, pp. 105) thought that the populations on islands were too small, variants would therefore occur too rarely, and the evolutionary process would therefore be too slow to account for all species.  (They did not know about genetic drift and how it can accelerate evolutionary change in small populations back then). Here is Darwin's reasoning against island biogeographies as the main origins of species:
"If, however, an isolated area be very small, either from being surrounded by barriers, or from having very peculiar physical conditions, the total number of the individuals supported on it will necessarily be very small; and fewness of individuals will greatly retard the production of new species through natural selection, by decreasing the chance of the appearance of favourable variations.
If we turn to nature to test the truth of these remarks, and look at any small isolated area, such as an oceanic island, although the total number of the species inhabiting it, will be found to be small, as we shall see in our chapter on geographical distribution; yet of these species a very large proportion are endemic,—that is, have been produced there, and nowhere else. Hence an oceanic island at first sight seems to have been highly favourable for the production of new species. But we may thus greatly deceive ourselves, for to ascertain whether a small isolated area, or a large open area like a continent, has been most favourable for the production of new organic forms, we ought to make the comparison within equal times; and this we are incapable of doing.
Although I do not doubt that isolation is of considerable importance in the production of new species, on the whole I am inclined to believe that largeness of area is of more importance, more especially in the production of species, which will prove capable of enduring for a long period, and of spreading widely. Throughout a great and open area, not only will there be a better chance of favourable variations arising from the large number of individuals of the same species [page break]
there supported, but the conditions of life are infinitely complex from the large number of already existing species; and if some of these many species become modified and improved, others will have to be improved in a corresponding degree or they will be exterminated. Each new form, also, as soon as it has been much improved, will be able to spread over the open and continuous area, and will thus come into competition with many others. Hence more new places will be formed, and the competition to fill them will be more severe, on a large than on a small and isolated area. Moreover, great areas, though now continuous, owing to oscillations of level, will often have recently existed in a broken condition, so that the good effects of isolation will generally, to a certain extent, have concurred. Finally, I conclude that, although small isolated areas probably have been in some respects highly favourable for the production of new species, yet that the course of modification will generally have been more rapid on large areas; and what is more important, that the new forms produced on large areas, which already have been victorious over many competitors, will be those that will spread most widely, will give rise to most new varieties and species, and will thus play an important part in the changing history of the organic world." Darwin (1859, p. 105f)

     However, if evolution through natural selection was defined as a mechanism that includes the principle of divergence as an active part, then Wallace does not have it either nor do modern evolutionary biologists, who mostly subscribe to a model of allopatric speciation. Such a position would distinguish Darwin's theory to the extent of isolating it from modern evolutionary biology. Therefore, it seems better to say that Matthew's scheme proposed species transmutation with natural selection in a lateral function, Wallace's scheme proposed species transmutation through natural selection in a biogeographic island setting, and Darwin's mature scheme proposed species transmutation through natural selection plus the principle of divergence (biogeography and isolation being facilitating factors).
    Finally, Derry reads Matthew as having natural selection and species transmutation, separately, but both do not work together in species transmutation. Hence, our three different readings of Matthew (1831, On Naval Timber and Arboriculture) can be aptly summarized as species transmutation through natural selection as the central factor (Weale), species transmutation with natural selection playing a lateral role (me), and species transmutation without natural selection playing a role during the lineage splitting and quick transmutation occurring after a catastrophe (Derry), but getting a species fixing role thereafter (where fixity does not exclude the possibility of anagenetic adaptation towards slowly changing conditions).

A comparison of the evolutionary mechanisms of Patrick Matthew, Charles Darwin, and Alfred Wallace highlights their differences. In Matthew’s scheme, catastrophes initiate periods of radiation and speciation until a fully stocked environment gets into stasis. Catastrophes first needed to exterminate competing species before the survivors could radiate into free niches and diversify into new species. In Darwin's early theory conditions of life, such as prevail under domestication, first need to increase the variability of a species, before natural selection can transform it. In Darwin's mature theory competition replaced conditions as the main drive behind evolutionary change and sympatric speciation becomes possible. Wallace’s theory differed from both Matthew’s and Darwin’s. Interspecific competition was neither a brake halting transmutation (as in Matthew’s) nor intraspecific competition a sufficient drive for it. While each theory integrated natural selection with variability, competition and changed conditions in distinct ways, each allowed for species transmutation somehow. The result was similar (transmutation), but the mechanisms yielding that result (the integration of natural selection with variability, competition, change in conditions) differed significantly.