Message by Pigeon
Throughout his cirripede odyssey Darwin kept up a number of parallel investigations bearing on his species theory from different angles, “to see how far they favour or are opposed to the notion that wild species are mutable or immutable,” he explained to his cousin Fox in March 1855. Central to his researches were, he said, “a number of people helping me in every way & giving me most valuable assistance.”40 Barnacles packed away, he now hoped that Fox would be among the first to assist with his newly rekindled interest in pigeons.
Darwin had long recognized the significance of domestic pigeons for his theory. Back in the late 1830s he even commented in one of his notebooks that pigeons are proof that variation in animals is not limited or constrained: “Analogy will certainly allow variation as much as the difference between species—for instance pidgeons [sic],” he wrote.41 Barnacles may have taken center stage as a diverse and little studied natural group of species that he could use to document variation and trace adaptation and descent, but those studies set the stage for the study of a complementary group, one that would serve as an artificial case study with its own expression of variation and demonstrated the power of selection. But what to study? Dogs or barnyard animals would not do: too big, and their development too long. His friend William Yarrell urged him to give pigeons a go. Of course! A group with diverse breeds, yet smallish animals easily kept inexpensively and in quantity, pigeons also grew fairly quickly and had the added bonus of being edible. And when I say diverse breeds, I mean diverse: breeds so divergent from one another that they would be easily placed in separate genera, let alone species, were they to be collected and classified by some alien naturalist. There were barbs and fantails, pouters and runts, trumpeters and carriers: pigeons with absurdly, sometimes grotesquely, modified heads, beaks, tail feathers, crops, feet—even behavioral variants like tumblers, with their neurological loose wire that makes them suddenly somersault in midair. Why were these strange breeds developed? Some, like carriers, are “working” pigeons, but pigeon breeding is called “the fancy” for an obvious reason: breeders take a fancy to this or that odd variant, and work diligently to develop it. Back in the mists of time this was probably not deliberate, but in more recent centuries it surely was. He knew pigeons had something to teach us: the often-absurd varieties and breeds carried a message about the power of selection.
It was conventional wisdom among zoologists that all pigeon breeds descended from just one wild species: Columba livia, the ubiquitous rock dove of city parks and country farmyards. Or did they? He was surprised to find that, unlike the zoologists, most fanciers believed that each breed was derived from a distinct wild ancestor. He recognized that this view, if widely held among the general public, would be one of many obstacles he would face in making a convincing case for common descent and the power of selection. But even the zoologists had little concept of how breeds were made. They often assumed new varieties appeared more or less fully developed, anomalous sports like the odd yellow rose popping up on a red rose bush. Their view is expressed by the prolific naturalist Daniel Jay Browne in his 1850 book The American Bird Fancier: “It is from the wild rock pigeon, (C. livia) that all those numerous varieties . . . of the common inhabitants of the dove cot have descended,” and that “the greater part of them owe their existence to the interference and art of man; for, by separating them from the wild rock pigeon, such accidental varieties as have occasionally occurred . . . and by assorting and pairing them together, as fancy or caprice suggested, he has, at intervals, generated all the various races.”42 Darwin would have read “variations” for “varieties,” variations that are more minute and abundant than Browne might have imagined. Subjected to Sebright’s “judicious selection,” variation upon variation leads to cumulative change over time.
Darwin was sure that the many breeds did not simply represent the domesticated descendants of a like number of ancestral wild species. Certainly the fossil record did not support a profusion of wild canines, bovines, and equines, for example, but maybe at most a few wild progenitors. (Indeed, recent DNA analysis shows that modern cattle, sheep, pigs, and goats likely descend from only two or a few ancestral species or subspecies each.) Darwin needed to prove this for pigeons. Luckily, by this time the use of embryology and development to inform classification was well appreciated, largely thanks to Henri Milne-Edwards’s important Essay on Classification of 1844. Darwin studied Milne-Edwards while working on his barnacles. Now he realized that by comparing the anatomy of certain domestic varieties from birth through maturation he should be able to show that breeds were identical in early stages and then diverged from one another at different points in development.
Darwin threw himself into the world of fancy pigeons with characteristic enthusiasm, but he didn’t go so far as to try to selectively breed them himself. Rather like connoisseurs or knowledgeable critics of fine art who are themselves no artists, Darwin studied and observed and immersed himself in the culture, getting to know fanciers at their meetings and visiting their aviaries and shows. And like art aficionados he became a collector, over the next two years procuring every pigeon breed available in Britain and more from further afield—some 16 breeds in all, over 90 birds cooing away in a veritable pigeon condo erected in the garden at Down House. He joined leading London pigeon clubs—the Philoperisteron and Southwark Columbarian—and gamely reported in a letter to Willy, then age 14 and away at boarding school, his adventures with the “strange set of odd men” that frequented them:
Four of the 16 pigeon breeds kept by Darwin (L to R): the pouter, with enormously inflated crop and foot feathers resembling spats; the English carrier, a sleek and strong-flying homing breed used to carry messages; the barb, with flattened, broad beak and large featherless eye-ring; and the fantail, with permanently fanned tail feathers reminiscent of displaying turkeys. From Darwin (1868), vol. I, figs. 18–21.
I want to attend a meeting of the Columbarian Society . . . I think I shall belong to this Society where, I fancy, I shall meet a strange set of odd men.—Mr Brent was a very queer little fish; but I suppose Mamma told you about him; after dinner he handed me a clay pipe, saying “here is your pipe” as if it was a matter of course that I should smoke. Another odd little man (N.B all Pigeons Fanciers are little men, I begin to think) & he showed me a wretched little Polish Hen, which he said he would not sell for £50 & hoped to make £200 by her, as she had a black top-knot.43
Bernard Brent was a leading pigeon fancier and, odd as he and the other “little men” of the Columbarian were, Darwin respected their expertise and was eager to be coached in the fine points of pigeon breeding.
The following February, 1856, found him as game as ever, writing to William on just having acquired some prize breeds: trumpeters, nuns, and turbits. “I am building a new house for my tumblers,” he was excited to report, “so as to fly them in summer.”44 Emma and the four youngest children were away visiting her sisters. It may have been then that Etty’s pet cat was quietly dispatched, having developed the habit of eating her father’s pigeons—something Etty never quite forgave. At one point Darwin’s pigeon mania led to another point of contention: the stench of curing and preparing the skeletons led to his pigeon lab being banished as far from the house as possible. Darwin, with his butler, Parslow, presided over the foul witch’s cauldrons of pigeon skeletons until even they couldn’t take it any longer, and he resorted to outsourcing the skeleton preparations. Owing (once again) to his network of friends and contacts, in short order he assembled an impressive set of skeletons of nearly every breed available in England and beyond.
Indeed, specimens alive and dead arrived daily at Down House, each of which he examined minutely. William Tegetmeier, sometime London writer, editor, beekeeper (as we shall see in Chapter 4), and pigeon fancier was a big help: “Many thanks for your offers about dead Pigeons,” Darwin wrote him. “If Scanderoon dies please remember I should wish carcase [sic] sent per coach by enclosed address as soon
as possible to arrive fresh.”45 His old college friend Thomas Eyton, who developed a sizable collection of bird skins and skeletons at his family estate, also obliged. Darwin explained to Eyton that he had taken up his pigeon project to compare the structure of pigeons at different stages of development; “I mean to try to get Domestic Pigeons from all parts of the world.” It wasn’t all one-way, of course: there was a gentlemanly exchange of specimens and information, as when Darwin proffered the preserved head of a Chinese breed of dog for Eyton’s study of dog skeletons: “I am delighted to hear that you are at dogs; it will be splendid for my work individually, & I am sure most desirable for Science. I have somewhere, I am almost certain, the head of a Chinese Dog: would you like to have this?” (He wrote a week later that he seemed to have misplaced it: “I have been looking everywhere for the Dog’s Head. . . . I am vexed at this.”)46
A Delightful Commencement
Barely a month before Darwin first expressed his pigeon fancy to Fox back in March 1855, a naturalist little known to Darwin, one Alfred Russel Wallace, was waiting out the rainy season in a small bungalow in Sarawak, in northern Borneo. Wallace passed the time gathering his thoughts on the striking parallel between species relationships geographically, in terms of their distribution on earth, and geologically, in terms of their distribution over time in the fossil record. He dashed out an essay and at the first opportunity mailed it off to London. Published the following September, this essay concluded that “every species has come into existence coincident both in space and time with a pre-existing closely allied species.” The principle became known as the Sarawak Law. Its evolutionary implications were clear to nearly all except Darwin: impressed, Lyell urged his friend to make haste and publish his species theory. Darwin was less impressed, maybe because he thought of Wallace as a mere collector. Expanding his interest to poultry, and adding chicken, duck, and turkey breeds to his menagerie, Darwin had evidently written Wallace to ask for specimens from southeast Asia. In late summer 1856 Wallace enclosed instructions with his latest consignment bound for London: “The domestic duck var[iety] is for Mr. Darwin & he would perhaps also like the jungle cock, which is often domesticated here & is doubtless one of the originals of the domestic breed of poultry.”47 Wallace also wrote Darwin directly, and in his reply Darwin alluded to the Sarawak Law paper, praising it in cautious terms and remarking “I can plainly see that we have thought much alike,” but he was coy about his own interests in species and varieties. He reiterated his desire to obtain “any curious breed” of poultry, and mentioned that Sir James Brooke, the “White Rajah” of Borneo, had kindly sent him pigeons, fowl, and cat skins.48
But Wallace was more than a collector. He was a confirmed transmutationist who collected in order to fund his travels investigating the “species question.” Having spent four years in Amazonia, he had just recently embarked on what was to become an 8-year odyssey crisscrossing the vast Malay Archipelago stretching from Singapore and Malaysia in the west to Papua New Guinea in the east. Little did Darwin know that in a short couple of years Wallace would succeed in his quest to find the mechanism of species change, natural selection. In the meantime, Darwin began to work away at his big species book, to be entitled Natural Selection. He progressed steadily, and by coincidence he just started writing up a section on pigeons in 1858 when a bombshell of a package from Wallace arrived, with a manuscript that laid out a formulation of natural selection. The brevity of Darwin’s journal entry speaks volumes: “June 14th Pigeons: (interrupted).”49 He was devastated.
The ensuing weeks were an emotional maelstrom as Darwin appealed to his friends Lyell and Hooker for help preserving his priority and honor even as his youngest child, baby Charles Waring Darwin, fell dangerously ill; he felt self-loathing for even caring about theories and priority at such a time. His friends hastily arranged for excerpts of Darwin’s unpublished outlines of the theory from the 1844 Essay and other sources to be read at the Linnean Society, along with Wallace’s paper. The papers were read on July 1st, but neither Wallace nor Darwin were present—Wallace still halfway around the world, and Darwin attending the funeral of his son. Within a few weeks, Darwin had regained enough composure to write Wallace explaining what had transpired. He then buckled down to finish his book and cement his priority. He was relieved to hear back that Wallace was delighted with all Darwin had accomplished thus far. Darwin knew he had to get his book out, but also knew that Natural Selection would take too long to complete. By the fall of 1858 Darwin resolved to pare it down. His “abstract,” as he called it, would become On the Origin of Species. Lyell recommended his own publisher, John Murray of London, and by April 1859 Murray had the manuscript in hand.
He asked a few colleagues to review it. One, the Scottish literary editor Rev. Whitwell Elwin, was singularly unimpressed with all but the section on pigeons. He recommended that Darwin get rid of the rest and produce a work on pigeons instead, smoothing the path for a later book expanding on his more unconventional views. “Even if the larger work were ready it would be the best mode of preparing the way for it. Every body is interested in pigeons,” Elwin said to Murray.50 Darwin was appalled, but was reassured that Murray didn’t take the recommendation seriously. Yet Elwin did have a point, in that Darwin had deployed his arguments on domestication in the very first chapter as a device to smooth the reception for the ideas of common descent and natural selection in subsequent chapters. Many of Darwin’s key arguments about natural selection were more speculative than well supported, and he was painfully aware that the Origin, which duly appeared in November of 1859, really was an abstract of his aborted big book, lacking the range of examples, data, and citations of authorities intended to make his original book unassailable. The remedy was to come out with more detailed treatments expanding on the main arguments of the Origin. In fact, his friend Thomas Henry Huxley encouraged Darwin to do precisely that in the weeks after the Origin appeared. Darwin was ahead of the curve: “You have hit on exact plan,” he assured Huxley, “which on advice of Lyell, Murray &c I mean to follow, viz bring out separate volumes in detail & I shall begin with domestic productions.”51
Domestication was the first line of argument in the Origin: Chapter 1 is all about modification of breeds by artificial selection as an analogy for how natural selection works in nature. He would thus begin with a supporting volume on domestication and follow it with a second volume dedicated to the case for natural selection (corresponding to Origin chapters 2–4), and then a third reflecting the rest of the book, tackling difficulties and detailing the empirical patterns evident in nature, from fossils to behavior to geographical distribution to comparative anatomy and more, a galaxy of dots neatly connected and facts explained by descent with modification by natural selection.
Darwin only produced the first of this projected series, and even that took nearly a decade: The Variation of Animals and Plants Under Domestication was published under Murray’s imprint in 1868. What had been treated in a single chapter in the Origin was now two volumes, and Darwin’s beloved pigeons, covered in a dozen pages in the Origin, now had two chapters of their own. Darwin’s strategy in these chapters is worth noting: in the first he detailed the characteristics of breeds, highlighting their diversity and rich variation in characters such as beak and skeleton relative to the rock pigeon as “parent-form.” Having made a convincing case for variation on a par with what naturalists would ordinarily associate with different genera, in the second chapter he then argued for a single origin of these breeds in all of their breathtaking diversity, culminating in a long final section entitled “Manner of formation of the chief races”—selection, both unconscious and methodical. It is here, in Darwin’s treatment of pigeons, that we find the only evolutionary tree ever produced by Darwin for any group of organisms. If domestic breeds in general represented a case study or microcosm of common descent and the power of selection in nature, for Darwin pigeons were a case study of a case study.
By 1868 Darwin was able to d
o for pigeons what he could not or would not do for barnacles in the 1850s: namely, trace an explicit evolutionary heritage. Why? It may have been the times; in those pre-Origin years of barnacle work he was perhaps simply unwilling to tip his hand and publish something too obviously (and controversially) transmutational before he was ready. But, perhaps, in an important respect, barnacles may have set the stage for this pigeon family tree—and indeed helped set the course for Darwin’s subsequent life’s work. It is ironic that his barnacle work is sometimes portrayed as a distraction that sidetracked Darwin from publishing his species book. On the contrary it was, first, the study that clued Darwin in to the sheer abundance of variation in all points of anatomy—that all-important ingredient for selection to act upon—and the variation he subsequently sought out in pigeons. Second, barnacles were his first overtly evolutionary investigation, one that saw the denouement of a new working method that entailed meticulous study, understanding the oddities of barnacle biology in terms of an evolutionary history, and, very importantly, developing a worldwide network of expert contacts that he could appeal to for assistance of all kinds. Darwin’s investigations of barnacles and pigeons may not have been experimental in nature, but illustrate a related working method no less important for us to understand the experimentiser.
Experimentising: Doing Your Barnacles
Of the many lessons that Darwin learned in his studies of barnacles and pigeons, perhaps the most important was gaining an appreciation for variability and how related groups of species represent variations on a theme: relationships can be traced by observing the same parts modified in different ways. To explore this idea in a hands-on way, “do your barnacles” like Darwin with these dissections.
Darwin's Backyard Page 9