At first sight it would seem as though a better example in support of “Natural Selection” could hardly have been chosen. Let the fact of the occurrence of occasional, severe droughts in the country which that animal has inhabited be granted. In that case, when the ground vegetation has been consumed, and the trees alone remain, it is plain that at such times only those individuals (of what we assume to be the nascent giraffe species) which were able to reach high up would be preserved, and would become the parents of the following generation.
For the sixth and last edition of the Origin of Species (1872), Darwin added the only chapter ever appended to his book—primarily to refute Mivart’s attack. This new chapter does discuss giraffes extensively (though only to rebut Mivart), and may be a primary source for the legend as later developed (for almost all reprintings and subsequent versions, up to our own day, feature this sixth edition, and not the first edition of 1859, which did not mention giraffe necks in the context of natural selection at all).
When we read Darwin’s careful words, however, we encounter yet another irony in our expanding list. The giraffe’s neck supposedly supplies a crucial example for preferring natural selection over Lamarckism as a cause of evolution. But Darwin himself (however wrongly by later judgment) did not deny the Lamarckian principle of inheritance for characters acquired by use or lost by disuse. He regarded the Lamarckian mechanism as weak, infrequent, and entirely subsidiary to natural selection, but he accepted the validity of evolution by use and disuse. Darwin does speculate about the adaptive advantage of giraffes’ necks, but he cites both natural selection and Lamarckism as probable causes of elongation. Thus, obviously, Darwin never regarded giraffe necks as an illustration for the superiority of natural selection over other valid mechanisms. He writes in two passages of the 1872 edition, marrying Lamarck with natural selection:
By this process [natural selection] long continued . . . combined no doubt in a most important manner with the inherited effects of the increased use of parts, it seems to me almost certain that an ordinary hoofed quadruped might be converted into a giraffe.
In every district some one kind of animal will almost certainly be able to browse higher than the others; and it is almost equally certain that this one kind alone could have its neck elongated for this purpose, through natural selection and the effects of increased use.
We may summarize the main line of this complexly meandering tale as a list of ironies—invoking the technical definition of irony as a statement where, for humorous or sarcastic effect, the intended meaning of a word becomes directly opposite to the usual sense—as in “that’s very smart!” for a proposal you regard as consummately dumb. In this story, none of the five historical facts arose by ironic intent. The irony occurs retrospectively, for each fact subverts the legend that “everyone knows” about tall giraffes—namely, that long necks for high leaves provide a splendid illustration for the superiority of Darwinian natural selection over Lamarckian use and disuse. The joke, in other words, is on the silly canonical legend as recounted in all modern textbooks.
1. Lamarck mentions giraffe necks in one passing paragraph of speculation within a chapter devoted to much longer examples regarded as far more important.
2. Darwin does not cite the case at all in the first edition of the Origin of Species. He does tell a giraffe story in the “just-so” mode, but from the opposite end—the tail rather than the neck. Darwin’s only quick phrase about giraffe necks illustrates the contrary theme of inherited stability (retained number of neck vertebrae) rather than novel adaptation.
3. When Darwin, in his longer and more technical book of 1868, does discuss giraffe necks in the context of natural selection, he does not present the standard “just-so story” of pure speculation, but rather uses giraffes to exemplify the difficult and crucial issue of how gradualistic natural selection can build a complex adaptation of many coordinated parts (the neck and all the supporting structures).
4. Mivart, in attempting to refute Darwinism, tells the “just-so story” that would become traditional, but only to caricature a theory he opposes.
5. When Darwin responds to Mivart in the last edition of the Origin of Species, he does interpret giraffe necks as adaptations for feeding on high leaves, but he argues that natural selection worked in concert with Lamarckian forces! (So much for a “classic” illustration of why the giraffe’s neck leads us to prefer Darwin over Lamarck.)
I don’t know (but would love to find out) how and where the legend’s modern form originated in such striking contrast to alleged historical sources. Henry Fairfield Osborn, the dominant paleontologist of his era, and longtime director of the American Museum of Natural History, gave the “standard” version in his popular book of 1918, The Origin and Evolution of Life:
The cause of different bodily proportions, such as the very long neck of the tree-top browsing giraffe, is one of the classic problems of adaptation. In the early part of the nineteenth century Lamarck attributed the lengthening of the neck to the inheritance of bodily modifications caused by the neck-stretching habit. Darwin attributed the lengthening of the neck to the constant selection of individuals and races which were born with the longest necks. Darwin was probably right.
This version has held ever since. Readers may well ask why we should devote energy to tracing such historical arcana. Why not let sleeping dogs lie and silly legends propagate, especially if tall tales do no harm? I gave some theoretical reasons for interest earlier in this essay, but I also wish to stress a practical concern. If we choose a weak and foolish speculation as a primary textbook illustration (falsely assuming that the tale possesses a weight of history and a sanction in evidence), then we are in for trouble—as critics properly nail the particular weakness, and then assume that the whole theory must be in danger if supporters choose such a fatuous case as a primary illustration. For example, in his anti-Darwinian book cited earlier (and eponymously titled The Neck of the Giraffe), Francis Hitching tells the story in the usual form:
The evolution of the giraffe, the tallest living animal, is often taken as classic evidence that Darwin was right and Lamarck wrong. The giraffe evolved its long neck, it is said, because natural selection choose those animals best able to feed off the highest treetops, where there is most food and least competition.
Hitching then adds: “The need to survive by reaching ever higher for food is, like so many Darwinian explanations of its kind, little more than a post hoc speculation.” Hitching is quite correct, but he rebuts a fairy story that Darwin was far too smart to tell—even though the tale later entered our high school texts as a “classic case” nonetheless. Eternal vigilance, as they say, is the price of freedom. Add intellectual integrity to the cost basis.
As a closing point, we might excuse this thoughtless repetition of an old legend without presumed historical sanction, if later research had established the truth of the tale nonetheless. But when we turn to giraffes themselves, we encounter the final irony of this long story. Giraffes provide no established evidence whatsoever for how their undeniably useful necks evolved.
All giraffes belong to a single species, quite separate from any other ruminant mammal, and closely related only to the okapi (a rare, short-necked, forest-dwelling species of central Africa). Giraffes have a sparse fossil record in Europe and Asia, but ancestral species are relatively short-necked, and the spotty evidence provides no insight into how the long-necked modern species arose. (The Giraffe: Its Biology, Behavior and Ecology, by A. I. Dagg and J. B. Foster, gives an excellent and thorough account of all major aspects of giraffe biology.)
When we study the function of long necks in modern giraffes, we encounter an embarras de richesses. Almost anything important in the life of a giraffe involves some use of the remarkable neck. Giraffes surely employ their long necks (and their long legs, long faces, and long tongues) to reach high-growing acacia leaves. Giraffes thereby browse several feet of vegetation exploitable by no other ground-dwelling mammal. The champ
ion giraffe reached an astonishing nineteen feet, three inches in height. Groves of African acacia trees (I have seen this phenomenon in the field) are often denuded below a sharp line representing the highest reach of local giraffes.
But giraffes also use their necks for other prominent and crucial activities. Male giraffes, for example, establish dominance hierarchies by frequent and prolonged bouts of “necking,” or swinging their large neck into the body of an opponent. These contests are more than merely symbolic, as the long neck propels the head with substantial force, and the bony horns atop the head can inflict considerable damage upon contact. Dagg and Foster describe a bout between two males named Star and Cream:
The two bulls . . . stood side to side, head to tail, dose together, each with his legs apart under him for balance. Suddenly Star lowered his head and whipped it, horns foremost, at Cream’s trunk, connecting with an impact that was heard easily from forty meters away. Cream lurched sideways, collected himself and returned the blow with his head, striking Star on the neck. Star then aimed at Cream’s front legs and knocked them out from under him with a blow of his head.
Dagg and Foster then describe the serious finality of potential outcomes:
The losing giraffe in such a struggle does not always escape so easily. His head may be gashed during a fight or he may be knocked to the ground unconscious . . . In such a contest in the Kruger National Park one of the contestants was killed. He had a large hole immediately behind one ear where his top neck vertebra had been splintered by a blow; part of the splinter had pierced the spinal cord.
Interestingly, giraffes fight predators (primarily lions) by kicking, but their sexual combats proceed by necking, never by kicking. Thus, this function of the neck may represent a specifically evolved behavior for a particular circumstance.
Giraffes also use their necks in several other ways: as a “lookout tower” to spot predators and other dangers, and as a device to increase surface area and shed heat (giraffes, unlike other large African mammals, do not seek shade and can remain in the sun). Both these functions have been viewed by prominent scientists as a chief reason for the evolution of long necks. In addition, giraffes deftly shift their center of gravity by appropriate movements of the neck—and these maneuvers are crucial to a wide range of activities, including rising from a lying position, running, and climbing fences and other barriers.
We may now return to the central theme of this essay—the dissociation of current utility from historical origin—and understand why the giraffe’s neck cannot provide a proof for any adaptive scenario, Darwinian or otherwise. Giraffes do use their long necks to browse leaves at the tops of acacia trees—but such current function, no matter how vital, does not prove that the neck originally evolved for this purpose. The neck may have first lengthened in the context of a different use, and then been coopted for better dining when giraffes moved into the open plains. Or the neck may have evolved to perform several functions at once. We cannot learn the reasons for historical origin simply by listing current uses.
When we consider the full range of current function, we can be fairly confident that some uses must be secondary, and cannot therefore be the source of historical origin. I can’t imagine, for example, that long necks evolved to help giraffes maneuver in running, jumping, and getting up—because the problem only arose when giraffes acquired a long neck in the first place, and solutions to problems can’t be causes of the problem.
But other functions may well be original—and the famous reaching for leaves could arise as a largely secondary effect. Since natural selection works fundamentally by differential reproductive success, and since sexual combat so often acts as a primary determinant of this basic Darwinian benefit, we could state a plausible case for regarding sexual success as the chief adaptive reason for evolving long necks, with the much-vaunted browsing of leaves as a distinctly secondary consequence. In short, we have no basis for any firm assertion about the most famous inquiry among Darwinian just-so stories: How did the giraffe get its long neck?
This essay therefore features a double whammy in pursuit of a primary theme—the dissociation of current utility from historical origin. In the realm of ideas, current invocation of the giraffe’s neck as the classic case of Darwinian evolution does not grow from firm and continuous historical roots. The standard story, in fact, is both fatuous and unsupported. In the realm of giraffes, current use of maximal mammalian height for browsing acacia leaves does not prove that the neck evolved for such a function. Several reasonable alternative scenarios exist, and we have no evidence for preferring any plausible version over another. Caveat lector.
Why, then, have we been bamboozled into accepting the usual tale without questioning? I suspect two primary reasons: we love a sensible and satisfying story, and we are disinclined to challenge apparent authority (like textbooks!). But do remember that most satisfying tales are false. The seventh-inning stretch predated Mr. Taft, and the story of kingly rising before the Hallelujah Chorus has no established foundation either. Polonius may have been an old bore, but he did give Laertes some good advice in the famous speech that Laertes surely failed to process because he was trying so hard to leave town. Among other tidbits, Polonius emphasized the importance of overt appearance—and we would do well to remember his counsel. Darwinian evolution may be the most truthful and powerful idea ever generated by Western science, but if we continue to illustrate our conviction with an indefensible, unsupported, entirely speculative, and basically rather silly story, then we -are clothing a thing of beauty in rags—and we should be ashamed, “for the apparel oft proclaims the man.”
17
BROTHERHOOD BY INVERSION (OR, AS THE WORM TURNS)
AS HAMLET, IN THE MOST CELEBRATED SOLILOQUY OF ENGLISH LITERATURE, weighs the relative values of life and death, he describes the attraction of suicide (“not to be”) as an escape from active insults, including “the oppressor’s wrong, the proud man’s contumely.” But writers and intellectuals worry far more about an opposite fate on life’s potential “sea of troubles”—erasure and oblivion, the pain of being simply ignored. Samuel Johnson, as recorded by Boswell, expressed this silent arrow of outrageous fortune in a famous aphorism: “I would rather be attacked than unnoticed. For the worst thing you can do to an author is to be silent as to his works.”
I therefore felt special poignancy when I recently read an anecdote about the last years of a great English physiologist, Walter H. Gaskell (1847-1914). After a distinguished career of solid experimental work on the function of the heart and nervous system, Gaskell switched gears and devoted the entire second half of his professional life (from 1888 on) to promoting and defending an idiosyncratic theory for the origin of vertebrates. The last paragraph of Gerald L. Geison’s long article on Gaskell in the Dictionary of Scientific Biography reads:
His final years were clouded . . . by a feeling that his deeply loved theory of the origin of vertebrates was not receiving a fair hearing. Even at Cambridge, where Gaskell lectured on the topic until his death, his audience decreased over the years until, near the end, the poignant scene is drawn of Gaskell closing his course by shaking hands with a lone remaining auditor.
We may grieve for Gaskell’s personal fate as an intellectual pariah; but, truth to tell, he had been pushing a pretty nutty theory for the origin of vertebrates. Gaskell believed with all his soul, and with a striking absence of critical questioning, that the evolution of animal life must follow a single pathway of progressive advance mediated by an increasing elaboration of the brain and nervous system. Gaskell wrote in his major work of 1908, The Origin of Vertebrates (the source of all quotes from Gaskell in this essay):
We can trace without a break, always following out the same law, the evolution of man from the mammal, the mammal from the reptile, the reptile from the amphibian, the amphibian from the fish, the fish from the arthropod [insects and their allies], the arthropod from the annelid [segmented worms], and we may be hopeful that the same law will ena
ble us to arrange in orderly sequence all the groups in the animal kingdom.
Gaskell identified this controlling principle of linear advance as the “law of the paramount importance of the development of the central nervous system for all upward progress.” In a rhetorical flourish, he then inverted the Preacher’s famous argument (Ecclesiastes 9:11) for randomness and aimless change without direction: “The law of progress is this—The race is not to the swift, nor to the strong, but to the wise.”
Advocates for a single line of progress encounter their greatest stumbling block when they try to find a smooth link between the apparently disparate designs of invertebrates and vertebrates. In addressing this old problem, Gaskell adopted the standard strategy of linear progress theorists from time immemorial: identify the most complex invertebrate and attempt to forge a link with the simplest vertebrate. Gaskell, again following tradition, selected arthropods as the invertebrate pillar for his bridge, and then tried to build the span by his law of neurological complexification. He wrote:
This consideration points directly to the origin of vertebrates from the most highly organized invertebrate group—the Arthropoda—for among all the groups of animals living on the earth in the present day they alone possess a central nervous system closely comparable in design with that of vertebrates.
So far, so conventional. Gaskell’s theory becomes idiosyncratic, and a bit bizarre, in his chosen mode for forging the improbable link of arthropod to vertebrate. Among the plethora of prominent differences between these phyla, one central contrast has always served as a focus for discussion, and a chief impediment to any linear scheme. Arthropods and vertebrates share some broad features of general organization—elongated, bilaterally symmetrical bodies, with sensory organs up front, excretory structures in the back, and some form of segmentation along the major axis. But the geometry of major internal organs could hardly be more different, thus posing the classical problem that has motivated several hundred years of dispute and despair among zoologists.
Leonardo’s Mountain of Clams and the Diet of Worms Page 30
