Leonardo’s Mountain of Clams and the Diet of Worms

  Though names and places vary maximally, we tell exactly the same (undoubtedly false) story to explain each ritual. An English king (someone between George II and George IV, depending on your favored version) found Handel’s majestic music so moving that he stood in honor—and audiences have done so ever since. An American president (William Howard Taft by consensus) got up at a ball game to stretch his legs, and everyone rose to honor the office.

  I love these tales because, in more reasonable attributions of motive, they so beautifully embody a fundamental theme of historical explanation—that consequences of substantial import often arise from trivial triggers of entirely different intent. In other words, current utility bears no necessary relationship with historical origin. Who knows why good King George-the-whatever stood up? Maybe he thought the intermission had already come? Maybe he was bored, or wanted to go out for a smoke? As for Taft, he probably got up to leave early (some versions even recount the story this way). Has any president ever stayed for an entire game? But think of the aggregated consequences ever since—millions upon millions of people standing at the appointed time. Gazillions of joules in spent energy. All manner of secondarily accreting traditions, as people who never otherwise sing outside the shower, for example, lustily exclaim, “Take me out to the ballgame.” And all because a king or a president once tried to sneak out early, or slip out for a pee. Substantial consequences from utterly insignificant origins.

  I raise this theme because I recently realized that the primary “old standard,” the classic textbook illustration of our preferences for Darwinian evolution, arose in the same manner—as an entrenched and ubiquitous example based on an assumed weight of historical tradition that simply does not exist. Several years ago, I made a survey of all major high school textbooks in biology. Every single one—no exceptions—began its chapter on evolution by first discussing Lamarck’s theory of the inheritance of acquired characters, and then presenting Darwin’s theory of natural selection as a preferable alternative. All texts then use the same example to illustrate Darwinian superiority—the neck of the giraffe.

  Giraffes, we are told, got long necks in order to browse the leaves at the tops of acacia trees, thereby winning access to a steady source of food available to no other mammal. Lamarck, the texts continue, explained the evolution of long necks by arguing that giraffes stretched and stretched during life, elongated their necks in the process, and then passed these benefits along to their offspring by altered heredity.

  This lovely idea may embody the cardinal virtue of effort rewarded, but heredity, alas, does not operate in such a manner. A neck stretched during life cannot alter the genes that influence neck length—and offspring cannot reap any genetic reward from parental striving. We therefore prefer the Darwinian alternative, consistent with the Mendelian nature of heredity, that giraffes with fortuitously longer necks (in a varying population with a large range of neck lengths among individuals) will tend to leave more surviving offspring. These progeny will inherit the genetic propensity of their parents for greater height. This slow process, continued for countless generations, can lead to steady increase in neck length, so long as local environments continue to favor animals with greater reach for those succulent topmost leaves.

  We often symbolize movements and beliefs by icons of clear meaning based on shared cultural histories. Thus, Americans may proclaim political affiliations by sporting a pin with a donkey or an elephant. More specifically, and among donkeys, a button with nothing but a saxophone identified “Friends of Bill” in Mr. Clinton’s presidential campaign, just as a pin of a shoe with a hole (recalling a famous photo of a tired candidate) once rallied the supporters of Adlai Stevenson. Similarly, the tallest of mammals, sticking his neck up, stands for evolution, and particularly for Darwin’s mechanism of natural selection. When Francis Hitching wrote a recent iconoclastic book, for evolution but against Darwinism, he chose as his title The Neck of the Giraffe—even though his text barely mentions the creature.

  A story so often repeated should rise from firm foundations and bear both strong and graceful support throughout the length of construction. In short, this most familiar of all examples should, like the subject’s own head, stand tall above everything else, buttressed by a device as supple and as well designed as “the neck of the giraffe.” Or, to recall the second image of my opening sentence, and to quote from the greatest of all love poems (called, not inappropriately, the Song of Songs): “Thy neck is as a tower of ivory . . . This thy stature is like to a palm tree.”

  If, instead, we traced this ubiquitous example back to scraps of speculation, and discovered either no foundation at all, or a funny little point of origin equivalent to a king in need of a bathroom break, then we might learn two lessons of potential import: first, that repetition need not correlate with truth value, and that even the most pious certainties should be periodically scrutinized right down to their foundations; and second, that the current importance and utility of a phenomenon gives us no particular insight into the circumstances of its historical origin.

  When we look to presumed sources of origin for competing evolutionary explanations of the giraffe’s long neck, we find either nothing at all, or only the shortest of speculative conjectures. Length, of course, need not correlate with importance. Garrulous old Polonius, in a rare moment of clarity, reminded us that “brevity is the soul of wit” (and then immediately vitiated his wise observation with a flood of woolly words about Hamlet’s madness). Many of the most famous Bible stories occupy only a verse or two, while lists of laws and begats go on for pages.

  Yet length must bear at least a rough relationship to perceived depth of meaning. Few authors will write chapters on matters deemed trivial and then devote only a line to their own most treasured theme—if only because readers will then be unable to weigh the relative importances properly. I feel quite confident that the authors of the Old Testament did grant greater meaning to their genealogies and laws—the basis of order and power in their own society, after all—than to the story of Jonah and the whale (the shortest chapter in one of the Bible’s shortest books). Our contemporary inversion—for fish stories now trump long lists of begats for unknown people with unpronounceable names—merely illustrates my chief point that current utility must be separated from historical origin in any judgment of importance or meaning.

  The giraffe’s neck just wasn’t a big issue for the founders of evolutionary theory—not as a case study for arguing about alternative mechanisms, not for anything much at all. No data from giraffes then existed to support any particular theory of causes over another, and none exist now. Absence of data rarely stops an imaginative scientist from speculating, I admit, but you can generate just so many words before a paucity of information dries up your thoughts. And no decent natural historian—let us hope, at least—will use a purely speculative case as a primary illustration of a central theory.

  Lamarck did mention giraffe necks as a putative illustration of evolutionary enlargement by the inherited effects of lifetime effort. But his entire discussion runs for one paragraph in a chapter filled with much longer examples that Lamarck obviously regarded as far more important. Lamarck had this to say—and absolutely nothing more—about giraffe necks, a few lines of speculation never intended as the centerpiece of a theory:

  It is interesting to observe the result of habit in the peculiar shape and size of the giraffe: this animal, the tallest of the mammals, is known to live in the interior of Africa in places where the soil is nearly always arid and barren, so that it is obliged to browse on the leaves of trees and to make constant efforts to reach them. From this habit, long maintained in all the individuals of the race, it has resulted that the animal’s fore-legs have become longer than its hind-legs, and that its neck is lengthened to such a degree that the giraffe, without standing up on its hind-legs, can raise its head to a height of six meters [from Lamarck’s classic 1809 work, Philosophic zoologique, volume 1, page 122, my translation].

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nbsp; This paragraph contains a giveaway statement—but you have to know the eighteenth-century literature to spot the clue—proving that Lamarck cared little about giraffes, and therefore didn’t grant this throwaway example much weight. Public zoos in the modern sense did not then exist in Europe, and few private menageries (usually maintained for royal patrons) had ever housed giraffes. Some travelers had seen giraffes in the wild, and many visitors had viewed them on display in Cairo. Giraffes had been known to Europeans since classical times, when Roman emperors included them in public slaughters at the Coliseum. Some reports had claimed, as Lamarck affirms, that the giraffe’s front legs greatly exceeded the back legs in height. In fact, both pairs of legs are equally tall. The impression of greater frontal height arises from the pronounced rearward slope of the giraffe’s back, a consequence of the massive muscles and spinal projections needed up front to support the huge neck. The most reliable sources available in Lamarck’s day had adequately established the equal length of fore and rear legs, and had dismissed the old myth of superior frontal elongation. Thus, if Lamarck repeated the old legend in his single paragraph about giraffes, he couldn’t have read the literature thoroughly.

  The example gained no particular steam as English writers explained Lamarck’s theory to their countrymen. Lyell’s remarkably fair exposition in opposition—given in the second volume of his Principles of Geology in 1832, and the source of most early English contact with Lamarck’s theory—quoted the example in abridgment, and made no further comment. In his famous series of lectures to workingmen (On Our Knowledge of the Causes of the Phenomena of Organic Nature), published in 1863 as the first great popular exposition of Darwinism, T. H. Huxley omitted giraffes entirely, and illustrated Lamarck’s theory with two examples emphasized by the Frenchman himself: the blacksmith’s strong right arm, putatively inherited by his sons; and the long legs and webbed feet of shorebirds, presumably evolved to avoid submersion or slipping in muddy ponds or flowing waters.

  When we turn to the horse’s mouth, the first edition of Darwin’s Origin of Species (1859), we find no mention whatever of the giraffe’s neck as an illustration of natural selection. Interestingly—and proving my point with panache—Darwin does cite the giraffe in just the context usually assumed for the legend of the neck: for a speculative story about the efficacy of natural selection. But, in this passage, Darwin treats the giraffe’s opposite end, and tells a tale about the tail. Moreover—because Darwin did not much favor the fatuous “just-so story” mode for illustrating natural selection by plausible speculation alone—his story about the giraffe’s tail occupies only a passing paragraph.

  Darwin raises this tale to contend that natural selection has sufficient power to explain “organs of trifling importance.” The giraffe’s tail, he argues, works primarily as a flyswatter. One might regard such a function as too trivial to fall under the purview of a mechanism based on differential survival (can swatting flies really become a matter of life or death?). Darwin replies:

  The tail of the giraffe looks like an artificially constructed fly-flapper; and it seems at first incredible that this could have been adapted for its present purpose by successive slight modifications, each better and better, for so trifling an object as driving away flies; yet we should pause before being too positive even in this case, for we know that the distribution and existence of cattle and other animals in South America absolutely depend on their power of resisting the attacks of insects: so that individuals which could by any means defend themselves from these small enemies, would be able to range into new pastures and thus gain a great advantage. It is not that the larger quadrupeds are actually destroyed (except in some rare cases) by the flies, but they are incessantlly harassed and their strength reduced, so that they are more subject to disease, or not so well enabled in a coming dearth to search for food, or to escape from beasts of prey.

  Darwin does mention the giraffe’s neck in a single line, but (ironically) for a purpose opposite to illustrating the power of natural selection in shaping organisms for particular utilities. In a closing section on evidence for evolution provided by homology, or retention of common ancestral structures in descendants of markedly divergent functional design, Darwin notes that the giraffe builds its remarkable neck not by adding new vertebrae, but by elongating the same seven bones present in the necks of virtually all mammals. Thus, history limits the power of natural selection by constraining adaptive solutions to the confines of inherited designs. He writes:

  The framework of bones being the same in the hand of a man, wing of a bat, fin of the porpoise, and leg of the horse,—the same number of vertebrae forming the neck of the giraffe and of the elephant,—and innumerable other such facts, at once explain themselves on the theory of descent with slow and slight successive modifications.

  In his subsequent, and longest, book, the two-volume Variation of Animals and Plants Under Domestication (1868), Darwin does finally introduce the giraffe’s neck in a discussion of natural selection. But again, and ironically given the later codification of the case as our canonical just-so story in the speculative tradition, Darwin does not cite “the neck of the giraffe” to tell a fatuous story about presumed adaptive advantages. Rather, he raises the example to discuss a more subtle issue central to the validity of natural selection as a general explanation of evolution.

  Even if we assume that the giraffe’s neck evolved as an adaptation for eating high leaves, how could natural selection build such a structure by gradual increments? After all, the long neck must be associated with modifications in nearly every part of the body—long legs to accentuate the effect, and a variety of supporting structures (bones, muscles, and ligaments) to hold up the neck. How could natural selection simultaneously alter necks, legs, joints, muscles, and blood flows (think of the pressure needed to pump blood up from the heart to the giraffe’s faraway brain)? In response to this problem, some critics had proposed that all relevant parts must be changed together in one fell swoop. Such suddenly coordinated modification would invalidate natural selection as a creative force because the desired adaptation would then arise all at once as a fortuitous consequence of internally generated variation. (Moreover, Darwin adds, we have no evidence for a deus ex machina of such complexly and luckily coordinated variation—and the whole proposal smacks of desperation and special pleading.)

  Darwin provides a cogent and subtle explanation (perhaps not thoroughly satisfactory by current views, but entirely logical and coherent). Interestingly, his proposal embodies the theme of this essay—the need to dissociate current utility from historical origin. A giraffe’s current functioning may require coordinated action of all parts that support the long neck, but these features need not have evolved in lockstep. If the neck grows by ten feet all at once, then every supporting bit of anatomy must be in place. But if the neck elongates an inch at a time, then the full panoply of supporting structures need not arise at every step. The coordinated adaptation can be built piecemeal. Some animals may slightly elongate the neck, others the legs; still others may develop stronger neck muscles. By sexual reproduction, the favorable features of different organisms may be combined in offspring.

  In developing this general explanation by using the giraffe as a putative example, Darwin does engage in conjectural biology. But I would defend this mode of speculation as a device utterly different from telling fatuous stories. When scientists need to explain difficult points of theory, illustration by hypothetical example—rather than by total abstraction—works well (perhaps indispensably) as a rhetorical device. Such cases do not function as “speculations” in the pejorative sense—as silly stories that provide no insight into complex mechanisms—but rather as idealized illustrations to exemplify a difficult point of theory. (Other fields, like philosophy and the law, use such conjectural cases as a standard device.)

  In thus invoking the giraffe as a proper exemplification, Darwin does embed a line within his text about adaptive advantages of reaching high. Taken out of
context, this comment could be read as a premonition of silly speculations to come. But its role as part of a conjectural case to illustrate a more subtle point of theory should be clear in the following totality (from Darwin’s 1868 book, volume 2, pages 220-221):

  With animals such as the giraffe, of which the whole structure is admirably coordinated for certain purposes, it has been supposed that all the parts must have been simultaneously modified; and it has been argued that, on the principle of natural selection, this is scarcely possible. But in thus arguing, it has been tacitly assumed that the variations must have been abrupt and great. No doubt, if the neck of a ruminant were suddenly to become greatly elongated, the fore-limbs and back would have to be simultaneously strengthened and modified; but it cannot be denied that an animal might have its neck, or head, or tongue, or fore-limbs elongated a very little without any corresponding modification in other parts of the body; and animals thus slightly modified would, during a dearth, have a slight advantage, and be enabled to browse on higher twigs, and thus survive. A few mouthfuls more or less every day would make all the difference between life and death. By the repetition of the same process, and by the occasional intercrossing of the survivors, there would be some progress, slow and fluctuating though it would be, towards the admirably coordinated structure of the giraffe.

  I suspect that the giraffe’s neck first became an explicit and contested issue within evolutionary theory when St. George Mivart, a fascinating rebel in many ways—as a devout Catholic in this Anglican land, and as an evolutionist firmly opposed to the mechanism of natural selection—published his 1871 critique of Darwinism, The Genesis of Species. Mivart did focus on the giraffe’s neck, and he did present Darwin’s supposed case in the form that has become canonical in modern high school textbooks—that is, as a speculative tale about natural selection. But note that Mivart wrote to oppose Darwinism, and that enemies tend to caricature and trivialize the doctrines they attack. Mivart stated: