Why Evolution is True is a blog written by Jerry Coyne, centered on evolution and biology but also dealing with diverse topics like politics, culture, and cats.
Before writing my notice of John van Wyhe’s new book on Wallace, Dispelling the Darkness, I hadn’t come across this piece by him on Wallace in last week’s Guardian. The piece addresses and dispels the claim, advanced a number of times over the years—especially in popular media—that Darwin stole his ideas from Wallace, and that there was an unsavory conspiracy to rob Wallace of proper credit. This is a view that has gotten some recent attention, and John deals with it head on. The short answers: he didn’t steal, and there wasn’t a conspiracy.
Do read the whole piece. Some excerpts:
Wallace deserves more attention but much of what you will have heard about him in the last few months is factually incorrect – and amounts to a misguided campaign to reinstate the reputation of a genius who (according to his fans) has been wronged by history and robbed of his rightful fame….
Darwin’s life and works have been meticulously studied by many scholars for over a century. But while some very able scholars have studied Wallace, he by contrast has remained mostly the preserve of amateurs and enthusiasts.
There has not been enough progress with our understanding of Wallace because some of the important research projects that have unveiled a treasure trove of new findings about Darwin had never been done for Wallace: his complete works had not been assembled on one scholarly website, his Malay archipelago expedition correspondence had not been collected and edited and his notebooks and journals had not been edited and their contents made intelligible.
All of these have recently been done, the latter two not yet published. These new sources have shown us that every substantive claim in the popular narrative about Wallace turns out to be incorrect.
And the money quote:
Darwin’s fame and reputation, and Wallace’s comparative obscurity, stem from the impact of Darwin’s Origin of Species. As Wallace himself wrote: “this vast, this totally unprecedented change in public opinion has been the result of the work of one man, and was brought about in the short space of twenty years!”
For my take on the second of these questions, which very much agrees with John’s, see my post on “Why is Darwin more famous than Wallace“. In attempting to promote Wallace, these modern admirers, perhaps unwittingly, portray Wallace as a hapless chump who was unaware of his own contributions. He was neither of these things.
The evidence from biogeography is arguably the most important evidence for evolution. P.J. Darlington, perhaps the greatest zoogeographer of the 20th century, said that zoogeography showed Darwin evolution. And Jerry has long insisted that biogeography is at least among, if not the, most persuasive evidence for evolution.
Canis antarcticus, by George Waterhouse, from the Zoology of the Beagle.
It was thus with great pleasure that I read a recent paper by Jeremy Austin and colleagues (ref below, news piece here) on the Falkland Islands fox or wolf (Dusicyon australis), a species which had intrigued Charles Darwin, and which he wrote about in the Zoology of the Beagle, the Voyage of the Beagle, and The Origin.
But first, let’s recap the features of island faunas that Darwin thought cried out for an evolutionary explanation. In examining island faunas, Darwin distinguished between continental islands, which had had a connection to a mainland in the recent past (e.g. Great Britain, which was connected to France by Ice Age sea-level lowering as recently as about 12,000 years ago), and oceanic islands, which had never had a connection to the main (e.g. mid-ocean volcanic islands like the Galapagos).
Darwin identified four characteristics of oceanic islands, which I like to call the “four D’s”. First, island faunas are depauperate— they hold fewer species than did comparable areas of mainland habitat. Second, they are disharmonious— they are inhabited by an unusual concatenation of taxa, rather than the usual combinations of predators, herbivores, and omnivores. Instead of cattle and deer, the large herbivores of islands were things like giant tortoises (as in the Galapagos) or giant geese (as in Hawaii). And large predators, such as cats and dogs, were usually lacking altogether (although some islands had very large birds of prey). Third, island faunas showed signs of dispersal— the animals that were there showed the ability to cross salt water. So birds and bats were usually present, but large land mammals and amphibians were usually absent. And finally, there was a strong effect of distanceon the character of the fauna– the Galapagos fauna, for example shows clear affinity to the Americas, while the fauna of the similarly situated but Atlantic archipelago of Cape Verde shows affinity to Africa.
Darwin argued that all of these features can be explained if the inhabitants of oceanic islands are the modified descendants of animals that had been able to disperse there. These animals would need be susceptible to occasional means of transport (dispersal), come from the most accessible mainland (distance), and would be a small, non-representative sample of what occurred on the mainland (disharmonious, depauperate). Darwin contrasted this with what we might expect under an hypothesis of special creation. Why were the island faunas “undercreated” relative to the mainland, and why would they bear the plain stamp of affinity to the nearest mainland, rather than being related to the faunas of other similar islands?
Although we all associate Darwin with the Galapagos, Darwin also visited the Falklands, and they supplied, I believe, an important bit of evidence in his thinking about islands. Darwin was a bit perplexed about the Falklands. In many ways they seemed like oceanic islands. There was only a single species of land mammal, the Falkland Islands fox, which was clearly related to South American foxes (South America has a modest radiation of canids, which are variously called dogs, foxes, or wolves in English). The mammal fauna thus shows 3 of the four D’s: depauperate, disharmonious, and distance.
Bathymetry between the Falklands and the main. Level III corresponds to the usual estimate of maximum glacial sea-level lowering (120 m), while level IV (140 m) is preferred by Austin et al. (from whom the figure is modified).
An alternative explanation for island faunas being depauperate and disharmonious is that the ecological conditions on the islands are unsuitable, despite seemingly appropriate physical environmental conditions. This alternative explanation is easily tested by introducing exotic species to the island, and seeing how they fare. If they become established, then the cause of their absence is a failure of dispersal, not a failure of environmental suitability. This is where the Falklands helped Darwin, I think. The Galapagos in the 1830s were still nearly pristine, but the Falklands showed him the fauna of an island with little direct habitat disturbance and a small human population, but whose population had brought their animals with them. At the time of his visit, Darwin recorded wild populations of cattle, horses, pigs, rabbits, rats, and mice, with feral cats and at least domestic dogs and sheep coming later. The Falklands were thus quite capable of supporting a diverse and harmonious mammalian fauna; the mammals just needed help getting there. (The increasing human population, and consequent increased disturbance and hunting, led to the extinction of the Falklands fox by the late 1800s.)
But how did the fox get there? Carnivores, in general, are not known to be good at dispersing across sea barriers, and a fox is unlikely to have been able to cross several hundred kilometers of open sea. This is what puzzled Darwin, and led him to suggest that the islands had been connected to the continent, despite the lack of all other animals that might have been expected to cross over on a land bridge. In later years, it was even suggested that the fox was semi-domesticated, and had been brought to the islands by Indians. This is where the latest paper by Austin et al. comes in.
As I noted above, South America is home to a modest radiation of canids, but the closest living relative of the Falklands fox, the maned wolf (Chrysocyon brachyurus), is not very close, with an estimated divergence time of 7 million years ago. What Austin and colleagues have done is extract DNA from fossils of Dusicyon avus, a very recently extinct canid (ca. 3ooo years ago) that was widespread in southern South America. Comparing their DNA to that from skins of the even more recently extinct Falklands fox, they found that the two are very closely related. Indeed, in their best phylogenetic estimate, the mainland avus is paraphyletic with respect to australis, and this is exactly what we would expect if the Falklands had been colonized by mainland foxes from the part of South America nearest to the islands. Furthermore they were able to date the divergence to 16,000 years ago– the height of the last glacial maximum. As is well known, the glaciers withdrew massive amounts of water from the sea, lowering sea levels by about 120 m. Looking at the seabed between the Falklands and the main, we can see that a 120 m lowering would substantially reduce the distance between them. Austin and colleagues favor an even greater lowering, further reducing the distance, but either lowering would reduce the distance to the order of tens, rather than hundreds, of kilometers.
But could a fox cross even tens of kilometers of sea? Yes– on ice floes or sea ice. How do we know? The arctic fox (Vulpes lagopus) ventures way out on to the sea ice, and can float out on ice floes, having been recorded as turning up occasionally in eastern Canada, far to the south of its native range. It is also the only native land mammal of Iceland, an island which has never had a continental land connection, and which it must have reached on ice floes. Darwin himself noted the possibility of ice transport, writing in the Origin “icebergs formerly brought boulders to its [Falklands] western shores, and they may have formerly transported foxes, as so frequently now happens in the arctic regions.”
So Darwin’s dilemma is solved. Glacial sea-level lowering and sea ice provide an “occasional means of transport”, and the fossil record and DNA analysis lead to an identification of the ancestor, and dating of the event to the precise time when such means were most available.
Austin, J.J. et al. 2013. The origins of the enigmatic Falkland Islands wolf. Nature Communications 4(1552). (pdf, subscription required)
Darwin, C.R. 1859. On the Origin of Species. London: John Murray. (DOL)
Darwin, C.R. 1860. Journal of Researches into the Natural History and Geology of the Countries Visited During the Voyage of H.M.S. Beagle Round the World. Last revised edition. London: John Murray. (DOL)
Matias, R. and P. Catry. 2008. The diet of feral cats at New Island, Falkland Islands, and impact on breeding seabirds. Polar Biology 31:609-616. (pdf)
Waterhouse, G.R. 1838. Mammalia. The Zoology of the Voyage of H.M.S. Beagle, under the Command of Captain Fitzroy, During the Years 1832 to 1836. Part 2, No. 1. (BHL, DOL)
The first publication of natural selection as a general mechanism of evolutionary change was a joint paper by Darwin and Wallace read to the Linnean Society in 1858. It was not a coauthored paper, but rather the simultaneous publication under a single heading of separate works by the two authors. So why does everyone know Darwin’s name, but hardly anyone knows Wallace’s?
My first reaction to the question is usually to say “But everyone does know about Wallace!” But I do find that even many biologists—especially if they are not evolutionary biologists—know little or nothing about Wallace. And in the culture at large, Darwin is well-known while Wallace is virtually invisible. (Since, at least in the United States, “Darwin” is a curse word to large swaths of the population, this may not be a bad thing for Wallace!) So there does need to be an analysis of the question of Darwin and Wallace’s relative contributions and recognition, and why Darwin is better known.
And the short answer is that their joint paper aroused little or no interest– it slipped into the waters of English natural history with scarcely a ripple. Thomas Bell, author of the herpetological volume of the Zoology of the Beagle and president of the Linnean Society in 1858, wrote at the end of the year that the Society had published no papers of special import during the year. It was the publication of the Origin of Species by Darwin the following year that made a splash heard round the world.
And there were several reasons for this: it was a work of monumental compilation and argumentation, eagerly anticipated by the leading lights of natural history both in Britain and abroad, and by a well respected and well known naturalist. It was the Origin, in fact, that forever associated Wallace with natural selection, through Darwin’s acknowledgment of Wallace’s co-discovery on page 1. Wallace himself always accepted that Darwin was primus inter pares.
The BBC piece follows the main currents of historical thinking in this regard, but makes two points worth emphasizing. First, it notes that Wallace was very well known in his lifetime, and that by virtue of his outliving Darwin he was for 30 years the sole surviving discoverer of natural selection, which enhanced his status and recognition from 1882 to 1913.
Second, it notes what Julian Huxley called the “eclipse of Darwinism”, a period in the decades around 1900 when natural selection (but not evolution) fell into disfavor (a period about which the historian Peter Bowler has written extensively), and that when natural selection was revalidated during the Modern Synthesis, Darwin was given more credit than Wallace. What is not noted in the BBC piece, but which I think may be significant, is that during the “eclipse” period, it was natural selection (i.e., Darwin and Wallace) that came under fire, but not evolution; and it was Darwin, much more so than Wallace, who convinced the world of evolution per se. So, during the “eclipse” period, Darwin was recognized for demonstrating evolution, but faulted for his mechanism of adaptive change (even T.H. Huxley sometimes inclined in this direction). In contrast, Wallace, whose chief contribution was natural selection, would simply be faulted. (Wallace’s many other contributions, especially in biogeography, were of course noted and lauded.)
The only thing that seemed off about the BBC piece was the title. Darwin did not “eclipse” Wallace, i.e., Wallace was not a shining star that some later passing dark object (Darwin) obscured. Rather, both were luminescent, and Darwin’s star had indubitably begun burning before Wallace’s. The question, then, is why was Darwin, on the public stage, more luminious than Wallace? But I suppose that the headline writer (who is almost always not the reporter) was trying to allude to the “eclipse of Darwinism” discussion, and it’s a small fault in an otherwise fine piece.
h/t Dominic
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Bowler, P.J. 1992. The Eclipse of Darwinism: Anti-Darwinian Evolution Theories in the Decades around 1900. Johns Hopkins University Press, Baltimore.
Bowler, P.J. 2005. Revisiting the eclipse of Darwinism. Journal of the History of Biology 38:19-32. (abstract only)
You’ll remember Congressman Paul Broun (R-Georgia), who infamously called embryology, the big bang, and evolution “lies from the pit of hell.” He was re-elected on Tuesday, running unopposed, but his statements did inspire a write-in campaign for an unlikely opponent: an Englishman, and a dead one at that– Charles Darwin! According to Athens Online, Jim Leebens-Mack of the University of Georgia started a “Darwin for Congress” Facebook page in response to Broun’s comments. Blake Aued at flagpole notes that it wasn’t just a Facebook page– Charlie himself hit the streets to campaign.
Charles Darwin, AKA Tim Denson, campaigns near the Arch with his wife, Jenny. Photo by Blake Aued, Flagpole.
And he got nearly 4000 votes! That’s nearly 2%– an enormous number for a write-in, and an unprecedented number for a dead Englishman running for Congress in northern Georgia in a presidential election year. Bill Nye, the Science Guy, who slammed Broun, a member of the House Science Committee, as “by any measure, unqualified to make decisions about science, space, and technology”, also received write-in votes. Charlie’s showing has inspired local politicians to commit to fielding a real candidate against Broun in 2014. According to Aued:
Neither Democrats nor more moderate Republicans have had any success against Broun, losing by 20-40 points in past elections. But Clarke County Democratic Committee Chairman Joe Wisenbaker says the party will “absolutely” field a candidate in 2014. “What we’re talking about doing is finding a well-qualified candidate who’s willing to change their name to Charles Darwin,” he joked.
Someone needs to run, so this national disgrace can be brought to an end.
During this 150th anniversary of the start of the Civil War, it is edifying to recall that Abraham Lincoln was not only a great president, but a great cat-lover. “Disunion”, the NY Times series on the 150th anniversary (which is generally quite good), in a piece on regimental mascots and pets, notes that
Even President Lincoln wasn’t immune to the solace provided by animals during the war. When Mary Todd Lincoln was asked if her husband had a hobby, she replied, “cats.”
Abraham Lincoln, our sixteenth President, loved cats and could play with them for hours. When asked if her husband had a hobby, Mary Todd Lincoln replied, “cats.” President Lincoln visited General Grant at City Point, Virginia in March of 1865. The civil war was drawing to a close and the enormous task of reuniting the country lay ahead, yet the President made time to care for three orphaned kittens. Abraham Lincoln noticed three stray kittens in the telegraph hut. Picking them up and placing them in his lap, he asked about their mother. When the President learned that the kittens’ mother was dead, he made sure the kittens would be fed and a good home found for them.
Darwin, who was born on the same day as Lincoln, preferreddogs.
BBC reporter Rebecca Morelle has been hot on the trail of the nearly extinct Hispaniolan solenodon in the mountains of the Dominican Republic. (There is another living species of solenodon in Cuba.) Here’s what they look like.
Male Solenodon cubanus. Plate 2, Allen 1910.
The BBC pursued them along with Dominican and British scientists, breathlessly recording their hopes of finding them, their adventures along the way, and their ultimate triumph (there’s also a kid’s version version of the story). The BBC articles have many videos and pictures, including one of a cat (next to last photo) emerging from a solenodon burrow– the kittehs are eating them!
Solenodons are among my favorite mammals, not just because they are so bizarre in their own right, but for the zoogeographic lessons we can learn from them and other island animals. In WEIT (and earlier writings), Jerry, despite being a geneticist, emphasized the biogeographic evidence for evolution. In doing so, he was following a long tradition, dating back to Darwin and Wallace themselves. P.J. Darlington (from Jerry’s and my alma mater, the MCZ), perhaps the greatest zoogeographer of the last century, said that zoogeography showed Darwin evolution.
Island faunas, especially of oceanic islands (i.e. islands never connected to a mainland, such as the Galapagos), exhibit what I like to call the three “D’s”: they are depauperate (having fewer species than equivalent pieces of mainland), they are disharmonious in their taxonomic composition (major groups from the nearest mainlands are missing, while others are curiously diversified), and show evidence of dispersal (the taxa in the fauna are able to travel over water).
The terrestrial mammals of the West Indies are definitely depauperate (there are many fewer species on Jamaica than in an equivalent piece of, say, Honduras). And they are disharmonious: the only major terrestrial mammal groups in the West Indies are insectivores (solenodons, and another, recently extinct, genus Nesophontes, called island-shrews), ground sloths (also recently extinct), monkeys (again, recently extinct), and a couple of groups of rodents (some recently extinct, but a modest number of survivors). They are completely lacking the most diverse groups of the surrounding mainlands: carnivores, both large (cougar, jaguar, bear) and small (raccoon, skunk, coati), hoofed mammals (deer, tapir, peccaries), opossums, and others.
The signs of dispersal are less clear in West Indian mammals. Rodents disperse over water well (by what Darwin called “occasional means of transport”), as, oddly, do sloths (they crossed from South to North America before the Panama land bridge formed); but insectivores and monkeys are not known for water-crossing. If we add in bats, we do see clear evidence of dispersal in the many species shared between islands and mainlands. But overall, some zoogeographers have seen the insectivores and monkeys as perhaps relicts of a former land connection, and the argument over whether the West Indies are oceanic or old continental islands (islands once connected to continents, but so long ago as to obscure the faunal characteristics: Madagascar is a classic example) is an old one in zoogeography. Indeed, the West Indies contain oceanic islands (the Lesser Antilles) and even recent continental islands (Trinidad), so that Cuba or Hispaniola being old continental islands would just complete the range of possible faunal conditions.
Female Solenodon cubanus. Allen 1910, plate 3.
Island faunas also show the two “E’s”: endemism (species being found on the islands and nowhere else) and extinction (island species go readily extinct when confronted by man, his habitat changes, and his many introduced species from the mainland). West Indian terrestrial mammals show high endemism (the solenodons and island-shrews are each endemic families, and there are others; no species is shared between islands and mainland), and also, regrettably, extinction: two of the four known solenodon species are extinct, and the living two are in trouble; about 80% of the 80 or so species of West Indian terrestrial mammals have become extinct in the last few thousand years.
Young Solenodon cubanus. Plate 1, Allen 1910.
Darwin (and Wallace) argued that all five of these “D” and “E” phenomena could be explained by descent with modification, creating a consilience of inductions: if organisms had to cross water barriers by occasional means of transport (floating, swimming, flying, etc.), rather than being created in situ, then some species and groups wouldn’t get there, those that did would diversify under different biotic conditions than those on the mainland, thus filling different places in the economy of nature, and thus not being adapted to the presence of mainland forms.
The plates here are from G. M. Allen’s classic 1910 monograph, published as one of the Memoirs of the Museum of Comparative Zooogy, on the anatomy of the Hispaniolan solenodon. Most have probably never been posted to the web, so I do so here. Here’s a Hispaniolan solenodon at the Museum of Comparative Zoology, from an unsourced photo I found on the web; it is perhaps one of the specimens studied by Allen a century ago..
Solenodon paradoxus at the MCZ
Allen, G.M. 1910. Solenodon paradoxus. Memoirs of the Museum of Comparative Zoology 40:1-54.
Allen, G.M. 1942.Extinct and Vanishing Mammals of the Western Hemisphere with the Marine Species of All the Oceans. Special Publication No. 11 American Committee for International Wild Life Preservation.
Coyne, J. A. 2005. The faith that dare not speak its name: the case against intelligent design. The New Republic Aug. 22, pp. 21-33.
Darlington, P.J. 1959. Darwin and zoogeography. Proceedings of the American Philosophical Society 103:307-319.
Darwin, C. 1859.On the Origin of Species. John Murray, London. Chap. 12, “Geographical Distribution”.
Morgan, G.S. & C.A. Woods. 1986. Extinction and zoogeography of West Indian land mammals. Biological Journal of the Linnean Society (London) 28:167-203.
