2. A tidbit with feathers. If birds evolved from small running dinosaurs, and if feathers could provide no aerodynamic benefit in an initial state of rudimentary size and limited distribution over the body, then feathers (which, by longstanding professional consensus and clear factual documentation, evolved from reptilian scales) must have performed some other function at their first appearance. A thermodynamic role has long been favored for the first feathers on the small-bodied and highly active ancestors of birds. Therefore, despite some initial skepticism, abetted by a few outlandish and speculative reconstructions in popular films and fiction, the hypothesis of feathered dinosaurs as avian ancestors gained considerable favor. Then, in June 1998, Ji Qiang and three North American and Chinese colleagues reported the discovery of two feathered dinosaurs from Late Jurassic or Early Cretaceous rocks in China (“Two Feathered Dinosaurs from Northeastern China,” Nature 393, 25 June 1998).
The subject has since exploded in both discovery and controversy, unfortunately intensified by the reality of potential profits previously beyond the contemplation of impoverished Chinese farmers—a touchy situation compounded by the lethal combination of artfully confected hoaxes and enthusiastically wealthy, but scientifically naïve, collectors. At least one fake (the so-called Archaeoraptor) has been exposed, to the embarrassment of National Geographic, while many wonderful and genuine specimens languish in the vaults of profiteers.
But standards have begun to coagulate, and at least one genus—Caudipteryx (“feather-tailed,” by etymology and actuality)—holds undoubted status as a feathered runner that could not fly. And so at least until the initiating tidbit for this essay appeared in the August 17,2000, issue of Nature, one running dinosaur with utterly unambiguous feathers on its tail and forearms seemed to stand forth as an ensign of Huxley’s intellectual triumph and the branching of birds within the evolutionary tree of ground-dwelling dinosaurs. But the new article makes a strong, if unproven, case for an inverted evolutionary sequence, with Caudipteryx interpreted as a descendant of flying birds, secondarily readapted to a running lifestyle on terra firma, and not as a dinosaur in a lineage of exclusively ground-dwelling forms (T. D. Jones, J. O. Farlow, J. A. Ruben, D. M. Henderson, and W. J. Hillenius, “Cursoriality in Bipedal Archosaurs,” Nature 406 [17 August 2000J).
The case for secondary loss of flight rests upon a set of anatomical features that Caudipteryx shares with modern ground birds that evolved from flying ancestors—a common trend in several independent lineages, including ostriches, rheas, cassowaries, kiwis, moas, and others. By contrast, lineages of exclusively ground-dwelling forms, including all groups of dinosaurs suggested as potential ancestors of birds, evolved different shapes and proportions for the same features. In particular, as the accompanying illustration shows, ground-running and secondarily flightless birds—in comparison with small dinosaurs of fully terrestrial lineages—tend to have relatively shorter tails, relatively longer legs, and a center of gravity located in a more forward (headward) position. By all three criteria, the skeleton of Caudipteryx falls into the domain of flightless birds rather than the space of cursorial (running) dinosaurs.
Jones and colleagues have presented an interesting hypothesis demanding further testing and consideration, but scarcely (by their own acknowledgment) a firm proof or even a compelling probability. Paleontologists have unearthed only a few specimens of Caudipteryx, none complete. Moreover, we do not know the full potential for ranges of anatomical variation in the two relevant lifestyles. Perhaps Caudipteryx belonged to a fully terrestrial lineage of dinosaurs that developed birdlike proportions for reasons unrelated to any needs or actualities of flight.
The flightless Cretaceous bird Caudipteryx (bottom) was closer in proportions to a modern emu or ostrich than to a bipedal dinosaur (top). The plus signs mark the torsos’ centers of gravity, and hip joints are indicated by dots.
I do not raise this issue here to vent any preference (for I remain neutral in a debate well beyond my own expertise, and I do regard the existence of other genera of truly feathered dinosaurs as highly probable, if not effectively proved).15 Nor do I regard the status of Caudipteryx as crucial to the largely settled question about the dinosaurian ancestry of birds. If Caudipteryx belongs to a fully terrestrial lineage of dinosaurs, then its feathers provide striking confirmation for the hypothesis, well supported by several other arguments, that this defining feature of birds originated in a running ancestor for reasons unrelated to flight. But if Caudipteryx is a secondarily flightless bird, the general hypothesis of dinosaurian ancestry suffers no blow, though Caudipteryx itself loses its potential role as an avian ancestor (while gaining an equally interesting status as the first known bird to renounce flight).
Rather, I mention this tidbit to close my essay because the large volume of press commentary unleashed by the hypothesis of Jones and his colleagues showed me yet again—this time for the microcosm of Caudipteryx rather than for the macrocosm of avian origins in general—just how strongly our trans-formational biases and our failure to grasp the reality of evolution as a branching bush distort our interpretations of factual claims easily understood by all. In short, I was astonished to note that virtually all these press commentaries reported the claim for secondary loss of flight in Caudipteryx as deeply paradoxical and stunningly surprising (even while noting the factual arguments supporting the assertion with accuracy and understanding).
In utter contrast, the hypothesis of secondary loss of flight in Caudipteryx struck me as interesting and eminently worthy of further consideration but also as entirely plausible. After all, numerous lineages of modern birds have lost their ability to fly and have evolved excellent adaptations for running in a rapid and sustained manner on the ground. If flightlessness has evolved in so many independent lineages of modern birds, why should a similar event surprise us merely by occurring so soon after the origin of birds? (I might even speculate that Cretaceous birds exceeded modern birds in potential for evolutionary loss of flight, for birds in the time of Caudipteryx had only recently evolved as flying forms from running ancestors. Perhaps these early birds still retained enough features of their terrestrial ancestry to facilitate a readaptation to ground life in appropriate ecological circumstances.) Moreover, on the question of timing in our admittedly spotty fossil record, Archaeopteryx (the first known bird) lived in Late Jurassic times, while Caudipteryx probably arose at the beginning of the subsequent Cretaceous period—plenty of time for a flying lineage to redeploy one of its species as a ground-dwelling branch.
Originally interpreted as a feathered dinosaur, Caudipteryx (left) may be a secondarily flightless bird. Oviraptor (right) was named “egg thief” because its skeleton was found atop fossilized eggs. Later studies showed it was probably protecting its own nest.
After considerable puzzlement, I think that I finally understand the reason for such a stark contrast between my lack of surprise and the sense of deep paradox conveyed by most press reports. As an implication of my view (expressing a professional consensus) that evolutionary novelty arises by a process of branching, the discovery of an earlier “first time” for a common and repeated event—loss of flight and secondary adaptation to effective ground running—surely attracts interest as a lovely nugget of discovery but scarcely evokes any theoretical surprise.
But in the usual public misconception of evolution as a story of wholesale transformation into something better, such an early “falling off from “the program” seems almost perverse. After all, birds had just taken to the air a few tens of millions of years (at most) before the appearance of Caudipteryx. Why would a lineage fall out of step so early in the game? Once the program rolls to a full and triumphant completion, then evolution might permit an ostrich or two to slip off the main line and pursue its own bohemian path in a now strange but once ancestral land. But such events surely cannot occur in the vigorous youth of a lineage that has just snatched winged victory from the jaws of terrestrial dinosaurian death.
Perha
ps I have treated a garden-variety error with unfair disdain in the sarcasm of the preceding paragraph. But the fallacy behind this common feeling of surprise, evoked by the eminently plausible hypothesis of Caudipteryx as a flightless bird, originates in a pervasive bias that renders much of the fascination of evolution inaccessible to millions of genuinely interested students and lovers of science.
The vigorous branching of life’s tree, and not the accumulating valor of mythical marches to progress, lies behind the persistence and expansion of organic diversity in our tough and constantly stressful world. And if we do not grasp the fundamental nature of branching as the key to life’s passage across the geological stage, we will never understand evolution aright. Tennyson caught the essence of life’s challenge when he personified nature’s unforgiving geological ways, as expressed in the fossil record of extinction:
From scarped cliff and quarried stone
She cries, “A thousand types are gone:
I care for nothing, all shall go.”
Yes, all shall eventually go, but some shall branch, thus permitting life to persist. To cite a sardonic song of self-mockery in leftist circles: “Trotsky got the ice pick [the weapon used by his murderers]. . . and so say all of us.” And I do shudder even to contemplate the fate of the poor tailor. But the totality of life feints, dodges, and branches—and therefore, above all, hangs on in beauty and fascination. Psalm 1 invokes the right picture for a different purpose: “And he shall be like a tree planted by the rivers of water . . . his leaf also shall not wither; and whatsoever he doeth shall prosper.” And Darwin employed the same image, both as metaphor and as literal topology this time, in the final words of the focal chapter in The Origin of Species—chapter 4, titled “Natural Selection,” with its closing literary flourish on extinction and branching as the motors of evolution’s tree and life’s glory:
As buds give rise by growth to fresh buds and these, if vigorous, branch out and overtop on all sides many a feebler branch, so by generation I believe it has been with the great Tree of Life, which fills with its dead and broken branches the crust of the earth, and covers the surface with its ever branching and beautiful ramifications.
VII
Natural Worth
24
An Evolutionary Perspective on the Concept of Native Plants
AN IMPORTANT, BUT WIDELY UNAPPRECIATED, CONCEPT in evolutionary biology draws a clear and careful distinction between the historical origin and current utility of organic features. Feathers, for example, could not have originated for flight because five percent of a wing in an evolutionary intermediate between small running dinosaurs and birds could not have served any aerodynamic function (though feathers, derived from reptilian scales, provide important thermodynamic benefits right away). But feathers were later co-opted to keep birds aloft in a most exemplary fashion (see essay 23 for a detailed discussion of this subject). In a similar manner, our large brains could not have evolved to permit modern descendants to read and write, though these much later functions now define an important aspect of the modern utility of consciousness.
Similarly, the later use of an argument, often in a context foreign or even opposite to the intent of originators, must be separated from the validity and purposes of initial formulations. Thus, for example, Darwin’s theory of natural selection cannot be diminished, either morally or scientifically, because later racists and warmongers perverted the concept of a “struggle for existence” into a rationale for genocide. However, we must admit a crucial difference between the origin and later use of a biological feature, and the origin and later use of an idea. The first, or anatomical, case involves no conscious action and cannot be submitted to any moral judgment. But ideas originate by explicit intent for overt purposes, and we have some ethical responsibility for the consequences of our deeds. An inventor may be fully exonerated for true perversions of his purposes (Hitler’s use of Darwin), but unfair extensions consistent with the logic of original motivations do entail some moral demerit (academic racists of the nineteenth century did not envision or intend the Holocaust, but some of their ideas did fuel the “final solution”).
I want to examine the concept of “native plants” within this framework—for this complex concept includes a remarkable mixture of sound biology, invalid ideas, false extensions, ethical implications, and political usages both intended and unanticipated. Clearly, Nazi ideologues provided the most chilling uses (see articles of J. Wolschke-Bulmahn and G. Groening, cited in the bibliography to this essay, for example). In advocating native plants along the Reichsautobahnen, Nazi architects of the Reich’s motor highways explicitly compared their proposed restriction to Aryan purification of people. By this procedure, Reinhold Tiixen hoped “to cleanse the German landscape of unharmonious foreign substance.” In 1942 a team of German botanists made the analogy explicit in calling for the extirpation Impatients parviflora, a supposed interloper: “As with the fight against Bolshevism, our entire Occidental culture is at stake, so with the fight against this Mongolian invader, an essential element of this culture, namely the beauty of our home forest, is at stake.”
At the other extreme of kindly romanticism, gentle arguments for native plants have stressed their natural “rightness” in maximally harmonious integration of organism and environment, a modern invocation of the old doctrine of genius loci. Consider this statement, for example, from a 1982 book by C. A. Smyser and others, titled Nature’s Designs: A Practical Guide to Natural Landscaping:
Man makes mistakes; nature doesn’t. Plants growing in their natural habitat look fit and therefore beautiful. In any undeveloped area you can find a miraculously appropriate assortment of plants, each one contributing to the overall appearance of a unified natural landscape. The balance is preserved by the ecological conditions of the place, and the introduction of an alien plant could destroy this balance.
In other words, these authors claim, evolution has produced a harmony that contrived gardens can only defy.
Or consider these words from former President Clinton (though I doubt that he wrote the text personally), in an April 26, 1994, memorandum “for the heads of executive departments and agencies” on “environmentally and economically beneficial practices on federal landscaped grounds”: “The use of native plants not only protects our natural heritage and provides wildlife habitat, but also can reduce fertilizer, pesticide, and irrigation demands and their associated costs because native plants are suited to the local environment and climate.”
This general argument boasts a long pedigree, as well illustrated in Jens Jensen’s remark in Our Native Landscape, published in his famous 1939 book, Siftings:
It is often remarked, “native plants are coarse.” How humiliating to hear an American speak so of plants with which the Great Master has decorated his land! To me no plant is more refined than that which belongs. There is no comparison between native plants and those imported from foreign shores which are, and shall always remain so, novelties.
Yet the slippery slope from this benevolent version toward dangerous Volkist nationalism may be discerned, and quite dramatically, in another statement from the same Jens Jensen—this time published in a German magazine in 1937.
The gardens that I created myself shall . . . be in harmony with their landscape environment and the racial characteristics of its inhabitants. They shall express the spirit of America and therefore shall be free of foreign character as far as possible. The Latin and the Oriental crept and creeps more and more over our land, coming from the South, which is settled by Latin people, and also from other centers of mixed masses of immigrants. The Germanic character of our cities and settlements was overgrown. . . . Latin spirit has spoiled a lot and still spoils things every day.
How tenuous the space between genius loci (and respect for all the other spirits in their proper places as well)—and “my locus is best, while others must be uprooted, either as threats or as unredeemable inferiors.” How easy the fallacious transition between a biolog
ical argument and a political campaign.
When biologically based claims engender such a range of political usages (however dubious, and however unfairly), we encounter a special responsibility to examine the scientific validity of the underlying arguments, if only to acquire weapons to guard against usages that properly inspire our ethical opposition. Any claim for preferring native plants must rest upon some construction of evolutionary theory—a difficult proposition to defend (as I shall argue) because evolution has been so widely misconstrued and, when properly understood, so difficult to utilize for the defense of intrinsic native superiority. This difficulty did not exist in pre-Darwinian creationist biology, because the old paradigm of “natural theology” held that God displayed both his existence and his attributes of benevolence and omniscience in the optimal design of organic form and the maximal harmony of local ecosystems. Native must therefore be right and best because God made each creature to dwell in its proper place.