Charles Darwin begins The Origin of Species by saying that while on HMS Beagle he was struck by two classes of facts: the strange distributions of plants and animals on Earth and the progression of forms in the fossil record from the oldest rocks to the youngest. These, and not variations in populations, first led him to doubt special creation and the fixity of species. Here, J. David Archibald shows how the facts of paleontology and biogeography led Darwin to suspect that organisms changed through time and eventually to develop the central theory of all of biology. Many people assume that because Darwin laid so much of the groundwork for the population biology of the Modern Synthesis (often called “Neo-Darwinism”), he must have had most of his inspiration for his theory of evolution from his observations of population biology. Quite to the contrary. Only after returning from his voyage on the Beagle and starting a home and family in Down did Darwin begin to circumscribe and observe populations in nature (Costa 2017). Even in his laboratory experiments, he was more concerned with individual variation and advantage than in comparing success of different populations. Ernst Mayr (1982) may have thought that Darwin’s entire theory revolved around population biology, but the fact is that the word “population” does not appear in the Origin of Species. This despite the enormous influence of Malthus’s (1798 and later editions through the sixth of 1826) Essay on Population, which every learned Englishman knew almost by heart (and Darwin mentions in his Introduction). It was the source not only of the insight that population will increase far faster than resources to sustain it, but of the inference that charity to the poor was counter-productive, because it would only encourage them to have more children whom they could not support. The centrist Whigs, including Darwin’s family, abhorred the doctrine, while the Tories used it to justify disdain of their equivalent of “entitlements.” Still, when the Origin first appeared, Darwin’s main nonreligious criticism came from two fronts: those who claimed he had not shown anything original and convincing, and those who said he had, but claimed that they had said it first. This obliged Darwin to insert an “Historical Sketch” of his idea into later editions; and it is interesting to observe how many of these claims recurred to the basic Malthusian “growth vs. supply” socio-economic theory. Even Darwin’s finches (not even finches but relatives of South American tanagers), the alleged source of his insight about the evolution of species, betray the myth of population biology. Frank Sulloway (1982) showed that Darwin initially did not keep separate his collections of birds from the different Galapagos Islands and had to rely on Captain FitzRoy and other crew members for their collecting notes; it was the London ornithologist John Gould who mainly identified and separated the different bird species and recognized their geographic diversity. What, then, was the stimulus that made Darwin reject the fixity of species and the doctrine of special creation? The answer is in the first lines of his Introduction to the Origin: “When on board H.M.S. ‘Beagle’, as naturalist, I was much struck with certain facts in the distribution of the inhabitants of South America, and in the geological relations of the present to the past inhabitants of that continent. These facts seemed to me to throw some light on the origin of species—that mystery of mysteries, as it has been called by one of our greatest philosophers.” That is, “distribution of the inhabitants” (biogeography) and “geological relations of the present to the past inhabitants” (paleontology and the succession of life). He doesn’t mention variation in populations. This is where David Archibald’s excellent new book begins. Darwin initially had to establish the fact of evolution, and he recurred first not to variation in populations, but to the macroevolutionary level. The idea that evolution occurred was sustained because it explained two great classes of fact: biogeographical distributions and the succession of “organic beings” in the fossil record. If special creation were true (and if there were “centers of creation,” as many held in those days), why did similar environments on different continents have similarly adapted plants and animals from such different taxonomic groups? Why were they not the same everywhere in similar environments? Darwin was struck by the gradual changes in plant and animal distributions across the length of South America, how the biota of the Galapagos Islands was clearly derived from that continent, and how different species were present on different islands. Migration and adaptation explained those patterns better than special creation. This was the importance of biogeography to the formation of evolutionary theory. In the same way, as Archibald shows, the pattern of faunal succession in the fossil record, before Lyell’s Principles of Geology was published in parts in the early 1830s, was seen as a succession of creations and extinctions separated by catastrophes. Lyell, although not a catastrophist, long thought that there was neither successive creation nor final extinction—rather, that the record was too poor to reveal the Paleozoic mammals that undoubtedly existed, and that, given the right environmental circumstances, ichthyosaurs and pterosaurs might return. Darwin could not disprove the pattern of absence of directional change in most “species-level” fossil lineages, and hence the absence of evidence that species evolved from other species. But he did think that the armored mammals of South America—the extinct glyptodont and the extant armadillo—shared features that were more than coincidental. (Ah, the importance of South America! Humboldt paved the way, as Darwin and everyone knew.) When Archaeopteryx was discovered, around the time the Origin was first published, Huxley encouraged Darwin to make use of it, but Darwin demurred: the status of the strange fossil was uncertain, and moreover, Darwin’s arch-enemy Richard Owen was describing it as a primitive bird but still with all the fully formed features of birds, so it could not have descended from a reptile. Darwin couldn’t afford to be wrong about it; anyway, it did not help his case on the transition of species. In later editions, as Archibald shows, he did treat it, but did not call it a transitional form. (This is a great and complex story that is well treated here.) It is telling that, following the publication of the Origin in 1859, the mechanism of natural selection as the main driver of the evolution of new species was not broadly accepted; but Darwin’s arguments for the unity of life and its descent from common ancestry were (Ellegård 1959). Importantly for the thesis of Archibald’s book, these latter depended not on Darwin’s observations of domesticated plants and animals, but on the geographical and geological succession of plants and animals in time and space. This fact is supported further by the change in meaning of the term “evolution” itself. Darwin avoided it in the Origin (“evolved” is its only use, the last word of the book) because at the time it had connotations of predestination, like the developmental unfolding of a fiddlehead fern or the shell of a snail. But in the wake of his book it took on its present, nonteleological meaning. These insights on biogeography and the fossil record preceded Darwin’s observational and experimental research that led him to the concept of Natural Selection as a prime mechanism for evolutionary change, as Archibald shows (see also Costa 2017). We tend to think of the latter topics as central to his work, because the Origin begins with chapters on artificial selection, natural variation, the struggle for existence, and natural selection, with chapters on biogeography, geology, fossils, and the rest placed later on. This was a better rhetorical strategy for Darwin, because no one could doubt the efficacy of artificial selection, and natural variation was easy to show. But Darwin was first convinced of evolution by patterns; only later did he deduce the processes behind them. The sequence of chapters in the Origin does not reflect this chronology. The topics in Origins of Darwin’s Evolution have been covered before, as its author admits, but seldom in so concise, clear, and up-to-date terms. We find how Darwin learned his geology and his plants; his brushes with Kelvin and the Victorian concepts of “Deep Time” and geochronology; how his biogeographical theory took shape; and how Darwin finessed the question of the incompleteness of the fossil record. Like David Quammen’s The Reluctant Mr. Darwin and Keith S. Thomson’s The Young Charles Darwin, this is one of those seemingly modest tomes that turns out to be indispensable for the Darwin scholar—and for everyone interested in the natural history of evolution. References Costa J.T. 2017. Darwin’s backyard. New York: W.W. Norton. Ellegård A. 1959. Darwin and the general reader: the reception of Darwin’s theory of evolution in the British periodical press, 1859– 1872. Chicago (IL): University of Chicago Press [reprint, 1990]. Lyell C. 1830–1833. Principles of geology (3 vols.). London: John Murray. Malthus R. T. (originally “Anonymous”). 1798. An essay on the principle of population as it affects the future improvement of society, with remarks on the speculations of Mr. Goodwin, M. Condorcet and other writers. London: J. Johnson in St Paul’s Church-yard. Mayr E. 1982. The growth of biological thought. Cambridge (MA): Belknap Press. Quammen D. 2006. The reluctant Mr. Darwin. New York: W.W. Norton. Google Scholar CrossRef Search ADS Sulloway F.J. 1982. Darwin and his finches: the evolution of a legend. J. Hist. Biol. 15: 1– 53. Google Scholar CrossRef Search ADS Thomson K.S. 2009. The young Charles Darwin. New Haven (CT): Yale University Press. © The Author(s) 2018. Published by Oxford University Press, on behalf of the Society of Systematic Biologists. All rights reserved. For permissions, please email: email@example.com This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/about_us/lega l/notices)
Systematic Biology – Oxford University Press
Published: Mar 6, 2018
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