Darwin's Backyard

by James T. Costa

  Now that he had a Cattleya to study, representing a whole new tribe, he proceeded to work out the peculiarities of its anatomy and pollination. The reason he wanted this orchid so badly is revealing: the structure of its pollinia was unlike any he had seen before, and so he knew the orchid’s mode of pollination would be unlike any other too. More importantly he thought that Cattleya pollinia were intermediate in structure between the two general types he had already studied, giving insight into stepwise pollinium evolution. This was an approach he followed to good effect in the Origin, showing how intermediate forms could be seen as evolutionary stepping stones of sorts, or precursors illuminating alternative pathways that natural selection might have taken. In either scenario intermediate forms help to link even the most highly divergent structures. So too with the highly modified pollination mechanisms of orchids, one aspect of which is their curious pollen packets. Darwin knew that one great group of orchids has pollen in a waxy ball without thread-like stalks, while another has a mass of pollen joined by elastic threads that form the stalks, or caudicles. The two are quite different, but Cattleya pollinia linked them. And so as an intermediate form he believed that Cattleya held the key to the very origin of pollinia: by eliminating this or that structure of Cattleya-type pollinia, virtually any other type could be made. “Hence,” Darwin declared, “I am inclined to look at this as the prototype.”15

  Pollen packets are one thing; another important matter is how they get transferred. He got to work mapping out the structure and release trigger of the flower. This is far easier said than done. Consider, for example, pollinia delivery in this species. First he needed to minutely map out where the pollinia are lodged—the dryness of his description a good indication of how he pored over the minutiae of structure and function: “The rostellum . . . is a broad, tongue-shaped projection, which arches slightly over the stigma: the upper surface is formed of smooth membrane; the lower surface and the central portions . . . consist of a very thick layer of viscid matter. This viscid mass is hardly separated from the viscid matter thickly coating the stigmatic surface which lies close beneath the rostellum. The generally projecting upper lip of the anther rests on, and opens close over, the base of the upper membranous surface of the tongue-shaped rostellum.”16 Ugh. But then, cleverly using a dead bumblebee as a sort of model, he mimicked how bees entered the flower, working out just how the pollinia end up on the bee’s back and how they are delivered to the next flower. The detailed description he eventually gave of the complex moving parts of these orchids would be eyeball-glazing to any but the most devoted orchid (or pollination) aficionado; suffice it to say that painstaking work went into ferreting out the secrets of each and every one of these complex flowers.

  At the start of his stay at Torquay, Darwin thought he would write a paper for the Linnean Society on the weird and wonderful pollination mechanisms of these plants. Long before the end of his stay he realized he had too much material: “My paper, though touching on only subordinate points will run, I fear, to 100 M.S. folio pages!!!” he lamented to Hooker; “The beauty of the adaptations of parts seems to me unparalleled.”17 It was about this time that he decided to present his findings in book form, which meant there’d be even more orchid studies. Having by then studied all available British orchid groups and a handful of foreign ones, he was keen to expand his study of orchid exotica and complete his examination of the rest of Lindley’s orchid tribes. But just as importantly, it gave him space to expand upon what he took to be the philosophical significance of orchids—an important subtext of his book as we shall see later in the chapter.

  Shaking the Foundation

  The family returned home near the end of August, an enjoyable holiday despite the weather being a bit damp and chilly. While on the coast, Uncle ’Ras, Charles’s brother Erasmus and a great favorite of the kids, had come down from London for a spell, and his cousin Fox’s son visited them too. Emma took Etty and one of her Wedgwood nieces off on an excursion to Dartmoor, the strikingly beautiful and barren moorland of Devon, in southwest England (now a national park). Charles managed country walks, collecting, writing, orchid observing, experiments (he could not resist the sundews), and even a social call or two, visiting his friend Thomas Wollaston, the entomologist, who lived not far from Torquay. For another entomological friend, John Lubbock, he and the boys hunted for bristletails—the following year Lubbock published a study of these curious wingless insects.

  Etty had steadily improved, probably not helped along by the heavy doses of cod-liver oil prescribed by Hooker. If you’re wondering about a botanist prescribing medication, recall from Chapter 5 that Hooker was an M.D. who had served, in his early 20s, as assistant surgeon aboard HMS Erebus on its famous Ross expedition to Antarctica. The expedition enabled Hooker to establish his botanical bona fides, and with his medical bona fides he dispensed advice and prescriptions for his family and friends—hence Etty’s cod-liver oil regimen, in her case rubbed on the skin as she wasn’t able to stomach it.

  As summer gave way to fall, things continued to look up on the home front: September saw Frank and George back at Clapham School, and things were falling into place for their older brother William and his banking partnership. Etty was well enough to play croquet on the back lawn with Bessy and Horace, the healthiest she had been in over a year. In early October they enjoyed a visit from Miss Pugh, the children’s former governess, and later that month Emma took Etty to London to see a concert featuring the acclaimed Swedish opera star Jenny Lind and the pianist Felix Mendelssohn-Bartholdy. (A lover of music, Emma was a talented pianist herself, even taking a few lessons from Frédéric Chopin in her youth.) That fall Charles and Emma no doubt enjoyed a sense of relief they hadn’t felt in quite a while, especially with their daughter out of the woods. On the scientific front, however, there were ups and downs.

  Soon after returning home he approached his publisher, John Murray, about publishing a small book on orchids. Characteristically modest, he ventured that although he was “very apt to think that my Geese are Swans,” yet “the subject seems to me curious & interesting.”18 He even offered to pay for the illustrations himself, fearing such a book might be a financial loss to Murray. Murray had no hesitation and immediately offered generous terms, illustrations included. Darwin no sooner had a contract for the book than an illustrator was engaged: artist George Sowerby arrived at Down House on October 7th and stayed for the next 10 days preparing orchid drawings, in some cases working from live specimens and in others adapting illustrations from an orchid treatise borrowed from Kew. All was well as he forged on ahead with his orchid studies, though in the 2 weeks between settling terms with Murray and Sowerby’s arrival there is one revealing comment in a letter indicating he had down days too: on October 1st he closed a letter to Lyell with a rather startling declaration (perhaps half-joking, but only half): “I am very poorly today & very stupid & hate everybody & everything. . . . One lives only to make blunders—I am going to write a little book for Murray orchids & today I hate them worse than everything.”19

  What happened? The word “blunder” may be a clue: the letter was in reply to one from Lyell relating the latest work of the energetic young geologist Thomas Francis Jamieson, who was working on the glacial landscape of Scotland. Jamieson examined the so-called “parallel roads” of the Glen Roy valley, curiously parallel terraces of cobble seemingly etched into the green heath and circling the entire valley like a bathtub ring—a simile that is especially apt in this case as they are fossil beaches marking ancient water lines at different levels. Encouraged by Lyell and Darwin, and building on the work of Agassiz and others, Jamieson provided the nail in the coffin of Darwin’s explanation for the parallel roads, which Darwin had published over twenty years before (see Chapter 1). Jamieson’s painstaking reconstruction of the action of the former glaciers that dammed the valley and formed the parallel roads won him election to the Geological Society of London the following year. Darwin always called his misinterpretation of
the site his “greatest blunder.” In that letter to Lyell he magnanimously called Jamieson “a capital observer & reasoner” but also gave himself a kick in the pants: “A nice mess I made of Glen Roy!”

  Alternatively, the source of his frustration may have related more to the subject at hand: orchids. He could have been confounded trying to figure out his latest orchidaceous Rube Goldberg contrivance, or maybe he was kicking himself because he neglected to preserve any exotic orchid flowers he had studied and now he desperately needed them for illustrations. With Sowerby soon arriving he applied to Hooker for help, explaining that he hadn’t saved the flowers because at the time he had no intention of producing a book on the subject. But now, he beseeched Hooker, he needed them for illustrations. “If you can send me any, send them by Post in tin-cannister on middle of day of Saturday Oct. 5th; for Sowerby will be here.”20 Hooker came through, as usual. A large package of orchids soon arrived, followed a few days later with a single spectacular blossom of a rarity much coveted by Darwin: Catasetum saccatum, the bizarre lizard orchid of South America. Darwin called it “the most wonderful orchid I have seen,”21 and feared touching the flower and tripping its pollinia delivery before he could study it. This is an orchid modified to such a degree that new structures needed naming, in this case the long, slender processes of the rostellum that Darwin dubbed “antennae.” He showed that one of these was an ultrasensitive trigger that forcefully fires the pollinia. John Lubbock recounted what happened when “Mr Darwin [was] so good as to irritate one of these flowers” in his presence: “the pollinium was thrown nearly three feet, when it struck and adhered to the pane of a window.”22 Presumably people keeping these orchids in their greenhouses were careful not to accidentally set one off and get a pollinium in the eye—a botanical BB-gun that a horticultural Ralphie might have been warned about in a different kind of Christmas story.

  But there was more to this orchid genus than projectile pollinia. Darwin had also acquired specimens of Catasetum tridentatum, a relative of the lizard orchid that abounds along the lush banks of the wide Essequibo River in what is now Guyana, and the source of much wonder. Back in 1836 the German-British naturalist and explorer Sir Robert Hermann Schomburgk (1804–1865) presented to the Linnean Society a botanical curiosity: an orchid specimen bearing the flowers of not merely different species, but species from two different genera. The bulb produced several stems, some of which bore Monachanthus viridis flowers and, astonishingly, others with those of Myanthus barbatus. These were no Piltdown-style doctored specimens, that was clear. The plant was meticulously drawn and preserved in spirits so that botanists could inspect it. Schomburgk documented a second case too, suggesting the first wasn’t just a freak of nature, and then, writing from the former Dutch colony of Demarara along the river of the same name in the Guianas he alerted the Linnean Society to a further discovery: in the orchid collection of a Mr. Wortman was found a “vigorous plant” bearing flowers of Monachanthus viridis that then grew a stem producing those of Catasetum tridentatum. “This I saw myself,” Schomburgk wrote; “the bulb was young, but the flowers in every respect quite perfect.”23 At a time when the nature of species and varieties was still being puzzled and the idea of transmutation—evolutionary change—was anathema to most naturalists, Schomburgk’s revelations were astounding: could three species, in altogether different genera, somehow develop from one plant? Was this a rare case of transmutation in action? Could new species spring forth wholesale in some sort of monstrous budding process? In The Vegetable Kingdom John Lindley declared that “such cases shake to the foundation all our ideas of the stability of genera and species, and prepare the mind for more startling discoveries than could have been anticipated.”24

  Catasetum saccatum’s bizarre flower. (A) Front view of column. (B) Side view of flower, with all the sepals and petals removed except the labellum. (C) Section through the column, with all the parts a little separated. (D) Pollinium, upper surface. (E) Pollinium, lower surface, which lies in contact with the rostellum. From Darwin (1862a), figs. XXV and XXVI.

  Schomburgk’s keen eye noticed something that would prove to be the key Darwin needed to solve this botanical mystery. In his letter to the Linnean Society Schomburgk commented that though he had seen hundreds of C. tridentatum orchids along the Essequibo River, not one bore seeds, while the M. viridis orchids “astonished me by their gigantic seed-vessels.” These sexual differences were significant, Darwin realized—the putative three-species-in-one plant was not some chimera but represented the sexual forms of the same, single, species. Studying the flowers he determined that what they called Catasetum tridentatum was a male plant, Monachanthus viridis female, and Myanthus barbatus both—an hermaphroditic flower with male and female parts. It’s easy to see how botanists presented with such different flower morphs separately and at different times would have considered them different species and even genera—the same sort of thing has happened with sexually dimorphic insects where one naturalist named a species based on one sex while another conferred an altogether different name based on the other sex. Only later, by rearing or finding the two in copula, was it realized that the two “species” were really one and the same.

  Darwin was so excited about his discovery—and his botanical friends at the Linnean equally delighted at the light he shed on Schomburgk’s orchids—that he was invited to read a paper there on the subject, which he did on April 3rd.25 George Bentham, then president of the society, declared to Darwin that the paper “put us on a new and unexpected track to guide us in the explanation of phenomena which had before appeared so irreconciliable with the ordinary prevision and method shown in the organised world.”26 In the broader scheme of things his discovery might have been considered little more than an interesting case of observation triumphing over assumptions based on incomplete information, but Darwin realized it was more than this. He documented how Monachanthus, the female plant, nevertheless bore nonfunctional, rudimentary pollinia. He dissected and described these defunct pollinia, recognizing them as yet another object lesson against the still widespread misconception of “design” in nature. “We thus see that every single detail of structure which characterises the male pollen-masses is represented,” he wrote, “with some parts exaggerated and some parts slightly modified, by the mere rudiments in the female plant. Such cases are familiar to every observer, but can never be examined without renewed interest.” And then the kicker:

  At a period not far distant, naturalists will hear with surprise, perhaps with derision, that grave and learned men formerly maintained that such useless organs were not remnants retained by the principle of inheritance at corresponding periods of early growth, but were specially created and arranged in their proper places like dishes on a table (this is the comparison of a distinguished naturalist) by an Omnipotent hand “to complete the scheme of nature.”27

  “People, get real,” he was effectively saying. Here Darwin was repeating a key point made in the Origin: to him it was plain that rudimentary structures were clues to evolutionary change, but those opposed to his theory of evolutionary modification over time must invent all sorts of excuses for such apparently useless traits. Perhaps the most laughable of these was the assertion that rudimentary traits were specially created placeholders, facsimiles of structures which although not functional nonetheless have a role to play in preserving pattern or symmetry in nature—like setting every place at a table even though there are fewer diners, for the sake of completeness or symmetry. In this line of reasoning the Creator presumably felt that an absence of these traits, a lack of symmetry, would be somehow jarring to humans. Darwin had little patience for this kind of logic, and in Chapter 13 of the Origin his disdain is clear. Reflecting on the rudimentary structures of orchids, he said, we can only be astonished, “for the same reasoning power which tells us plainly that most parts and organs are exquisitely adapted for certain purposes, tells us with equal plainness that these rudimentary or atrophied organs, are imperfect and useles
s.”28 He pointed out that it was silly to maintain that rudimentary structures were created “for the sake of symmetry” or “to complete the scheme of nature.” Such so-called explanations were worse than no explanation at all, he fumed, and merely a restatement of fact. With a hint of sarcasm he asked if it would be “thought sufficient to say that because planets revolve in elliptic courses round the sun, satellites follow the same course round the planets, for the sake of symmetry, and to complete the scheme of nature?”29 This is in fact the subtext of Darwin’s orchid book, the Origin’s sequel of sorts: as with his cherished barnacles (see Chapter 2), orchids were a case study in evolutionary modification, with the same parts varied in seemingly endless ways from group to group, some even reduced or aborted, yet each well adapted for cross-pollination by insects. By the same token an argument for descent with modification is an argument against special creation and design, and he saw this as a key lesson taught by orchids. Or was it? Not everyone otherwise sympathetic to Darwin’s evolutionary ideas dispensed with the idea of design in nature.

  A Flank Movement on the Enemy

  Darwin’s friend Asa Gray might be the best spokesman for those who saw no incompatibility between evolution and the doctrine of natural theology, with divine design at its heart. Gray and Darwin had sparred over this issue ever since the Origin came out. In today’s terms Gray would be labeled a theistic evolutionist—one who accepts the fact of gradual evolutionary change over deep time and an ever-ramifying tree of life, but sees this as, at some level, a divinely directed process. How the Creator might direct evolutionary change is usually left unsaid; perhaps by divine guidance of the right mutations at the right time and place, or maybe by influencing the action of natural selection. As with every aspect of the theistic view this is necessarily speculative. Gray was nearly as much of a bulldog in defending the Darwin and Wallace theory as Huxley, but the devout botanist saw the hand of the Creator in the process. This still put him at odds with more conventional natural theology adherents, like Gray’s Harvard colleague Louis Agassiz, who denied any kind of evolutionary change. Gray debated with Agassiz in public, and through a series of spirited and well-argued articles in Atlantic Monthly magazine.30 Darwin was so impressed with these pieces that he helped bankroll their republication in pamphlet form in the United States and Britain, appearing in 1861 under the title Natural Selection Not Inconsistent with Natural Theology. That was a calculated move on Darwin’s part—he may not have agreed fully with Gray’s take on things, but at least his friend was arguing eloquently for natural selection and species change—a step in the right direction as far as Darwin was concerned.