The following blog post tries to explain how it came about that Patrick Matthew, Charles Darwin, and Alfred Wallace all thought about their evolutionary theories (first published in 1831 by Matthew and in 1858 jointly by Darwin and Wallace) as essentially identical, when closer analysis reveals significant differences (e.g., Dagg 2018). How could they, and many people ever since, have overlooked the differences?
Huxley's review of Darwin's Origin of Species
Thomas H. Huxley anonymously reviewed Charles Darwin's On the Origin of Species (1859). His review was first published in the Times (26 December 1859, pp. 8-9). The Gardeners’ Chronicle and Agricultural Gazette (3 March 1860, pp.192-193) reproduced it. Therein, Huxley gave examples of breeds (pigeons, swine, cattle) that grossly deviated from their wild ancestors and explained the process of artificial selection employed by the breeders before stating:
"But in all these cases we have human interference. Without the breeder there would be no selection, and without the selection no race. Before admitting the possibility of natural species having originated in any similar way, it must be proved that there is in nature some power which takes the place of man, and performs a selection sua sponte. It is the claim of Mr. Darwin that he professes to have discovered the existence and the modus operandi of this natural selection, as he terms it; and, if he be right, the process is perfectly simple and comprehensible, and irresistibly deducible from very familiar but well nigh forgotten facts." (Huxley 1860, 193, col. 3)
He then continued with the over-reproduction of all organisms, the struggle of survival and the survival of the fittest resulting from it. That is, Huxley's review was a simplification and popularization of Darwin's theory that every lay-reader of the time could comprehend. Most strikingly, Huxley's review completely lacked the principle of divergence by which Darwin laid so much stock, but which is now largely forgotten or, if not, causes much perplexity among biologists.
Darwin mentioned it in a letter to Asa Gray, 5 September 1857, (Darwin Correspondence Project, Letter no. 2136, accessed on 8 Jan. 2019, http://www.darwinproject.ac.uk/DCP-LETT-2136) stating: "One other principle, which may be called the principle of divergence plays, I believe, an important part in the origin of species." In a later letter to Joseph D. Hooker, 8 June 1958, (Darwin Correspondence Project, Letter no. 2282, accessed on 8 Jan. 2019, http://www.darwinproject.ac.uk/DCP-LETT-2282), he stated that the principle of divergence and natural selection will together form the key-stone of his book to come (On the Origin of Species). And in his Autobiography, edited by Nora Barlow (1958, 120), Darwin recounted an eureka moment, when he came across this principle while in a carriage on a road and he likened his solution to the one of Columbus and his egg.
Why was the principle of divergence important to Darwin?
Biologists, today, see island biogeographies everywhere. A hilltop in a flat country can be an island just as an isolated valley in the mountains. Rivers and other geographic barriers can create one island biogeographic setting for some species and a totally different setting for others depending on their ecological niches. Biologists see island biogeographies where Darwin saw none. Furthermore, they know about genetic drift as a mechanisms that accelerates evolutionary change in small populations in these settings.
Darwin, however, had found from taxonomic studies that taxa on continents were not only larger than on islands but also that their members (e.g., genera, species) were more divergent from each other than on smaller islands. He also believed that the smallness of the populations on islands would retard the process of evolution there simply by making favorable variants a rare occurrence. Therefore, he needed a principle that would explain this pattern. In other words, he needed something that would drive lineages apart on continents and in the absence of catastrophes or islands.
What was the principle of divergence?
His principle of divergence achieved this by proposing that the internal competition between varying individuals within species was disruptive enough to allow lineage splitting. Advantageous sports dodged being swamped somehow and, instead, managed to exterminate the intermediate (parental) form. If more than one such variant occurred simultaneously, and the variants could no longer interbreed after the extinction of the parental form, lineage splitting (speciation) had occurred without geographic isolation of the variants (in sympatry). Geographic isolation could facilitate this lineage splitting, but is was not a necessary prerequisite.
In this principle of divergence, Darwin's theory differed not only from Wallace's (who had an island biogeographic setting for lineage splitting) and Matthew's (who had catastrophes doing the lineage splitting), but also from Huxley's simplified review and from current evolutionary theory. The latter is, in my humble opinion, closer to Wallace's island biogeographic scheme than to Darwin's original scheme from 1859.
Matthew's priority claim
Matthew had read Huxley's review in the Gardeners' Chronicle from 3 March 1860 and sent his priority claim to that periodical at 7 March 1860. This is evident from the date and signature given by Matthew at the end of his letter to the journal. (It took the editors until 7 April 1860 to publish Matthew's claim.) It is unlikely that Matthew had consulted Darwin's book at length or in any detail within those four days. It seems far more likely that he had simply taken what he could gather from Huxley's review and written his priority claim on the spot, collating passages from his book that fit the simplified account given by Huxley.
Darwin's reply to Matthew's claim
Darwin's response was equally hasty (within 6 days). It got published on 21 April 1860 in the Gardeners' Chronicle (pp. 362-363). However, Darwin had sent his response to Joseph D. Hooker for approval on 13 April 1860 (Darwin Correspondence Project, Letter no. 2758, accessed on 8 January 2019, http://www.darwinproject.ac.uk/DCP-LETT-2758). Basically, Darwin had ordered Matthew's book (see letter to Charles Lyell, 10 April 1860, Darwin Correspondence Project, Let. 2754, accessed 8 Jan. 2019, http://www.darwinproject.ac.uk/DCP-LETT-2754), in order to make sure that the passages given by Matthew in his priority claim were scattered passages in a book on an otherwise different subject. This he made sure, in order to excuse himself for having overlooked Matthew's book in his long pondering on the subject. His response read:
"I have been much interested by Mr. Patrick Matthew’s communication in the Number of your Paper, dated April 7th. I freely acknowledge that Mr. Matthew has anticipated by many years the explanation which I have offered of the origin of species, under the name of natural selection. I think that no one will feel surprised that neither I, nor apparently any other naturalist, had heard of Mr. Matthew’s views, considering how brieﬂy they are given, and that they appeared in the appendix to a work on Naval Timber and Arboriculture. I can do no more than offer my apologies to Mr. Matthew for my entire ignorance of his publication. If another edition of my work is called for, I will insert a notice to the foregoing effect."
Wallace's review of Butler's Evolution Old and New
Alfred Wallace only returned from the Malay Archipelago in 1862. Consequently, he remained largely ignorant about Matthew's ideas until Samuel Butler sent him a complimentary copy of his book Evolution, Old and New (1879). Butler (1879) claimed that Darwin's theory was nothing but Lamarckism redux and that Matthew's theory was worlds apart in this. However, Butler mistook Matthew's catastrophism as necessarily putting him in one camp with Cuvier and opposite to Lamarck. Matthew had in fact married Cuvier's catastrophism to transmutationism (Lamarckian or otherwise). Apart from this nonsense, Butler also re-quoted the passages that Matthew had already re-quoted in his priority claim against Darwin in 1860 (except for one paragraph about spontaneous generation). Apparently, Wallace read these passages from Matthew only now for the fist time. He replied in a letter to Butler:
"To my mind, your quotations from Mr. Patrick Matthew are the most remarkable things in your whole book, because he appears to have completely anticipated the main ideas both of the Origin of Species and of Life and Habit." (Wallace to Butler, 9 May 1879)
Wallace published a review of Butler's book in the journal Nature (12 June 1879, Vol. 20: 141-144), in which he had the following to say about Matthew:
"We come next to Mr. Patrick Matthew, who in 1831 put forth his views on the development theory in a work on arboriculture; and we think that most naturalists will be amazed at the range and accuracy of his system, and will give him the highest credit as the first to see the important principles of human and “natural selection,” conformity to conditions, and reversion to ancestral types; and also the unity of life, the varying degrees of individuality, and the continuity of ideas or habits forming an abiding memory, thus combining all the best essential features of the theories put forth by Lamarck, Darwin, and Mr. Butler himself."
Wallace continued with re-quoting yet again, some of the re-quotes by Butler of Matthew.
Thus, a persistent historical pattern had been firmly established. From now on, every other decade, someone would stumble over Matthew (1831), be very surprised about his prescience and re-quote the same old passages once over, in order to emphasize how very identical these were to Darwin's and Wallace's theories. This would reiterate itself for the next century and a half without any proper historiography of the Patrick Matthew case ever emerging from this reiteration of a legend.