The Flamingo’s Smile

by Stephen Jay Gould

  Wells begins diffidently, fearful perhaps that too much speculation will dilute the value of his sober observations on Hannah West’s unusual skin:

  On considering the difference of color between Europeans and Africans, a view has occurred to me of this subject, which has not been given by any author, whose works have fallen into my hands. I shall, therefore, venture to mention it here, though at the hazard of its being thought rather fanciful than just.

  Wells invokes natural selection to explain the success of black people in hot climates. Beginning with the usual and unstated racist assumption that white skin is proper and primary, Wells imagines that the original inhabitants of Africa were lighter than their current descendants. He explains the change by natural selection and even invokes Darwin’s favorite argument of analogy with artificial selection as practiced by animal breeders:

  Those who attend to the improvement of domestic animals, when they find individuals possessing, in a greater degree than common, the qualities they desire, couple a male and female of these together, then take the best of their offspring as a new stock, and in this way proceed, till they approach as near the point in view, as the nature of things will permit. But, what is here done by art, seems to be done, with equal efficacy, though more slowly, by nature, in the formation of varieties of mankind, fitted for the country which they inhabit.

  This statement has been cited in several previous works (it is the “standard” quote from Wells), but I do not think that any previous commentator has recognized the decidedly unorthodox character of Wells’s presentation. Curiously, its unusual features presage some of the arguments now being presented by many evolutionists against the strict construction of Darwinism that has been so popular during the past twenty years or so.

  The conventional, strictly Darwinian, argument would feature direct adaptation of skin color and evolutionary change driven by competition among individual organisms. In other words, we would argue that black skin offered direct advantages in hot climates and that it arose by differential survival and propagation of darker individuals within a population. Wells explicitly denies both parts of this scenario.

  For adaptation, Wells rebuts the idea that black skin provides any benefit in itself (he was probably wrong) and claims instead that some other physiological feature adapts black people to hot climates by conferring resistance to tropical diseases. Wells speculates that this feature may be subtle and not manifested in evident morphology. Black skin may be correlated with this feature for some unknown developmental reason and may therefore serve as a signpost of advantage, while providing no direct benefit itself:

  I do not, however, suppose, that their different susceptibility of diseases depends, properly, on their difference of color. On the contrary, I think it probable, that this is only a sign of some difference in them, which, though strongly manifested by its effects in life, is yet too subtle to be discovered by an anatomist after death; in like manner as a human body, which is incapable of receiving the small-pox, differs in no observable thing from another, which is still liable to be affected with that disease.

  Darwin puzzled over these “correlations of growth” and recognized that many features may offer no direct benefit, yet still characterize large groups by their forced physiological relationship with other traits. Extreme versions of Darwinism have forgotten this subtlety and have tried to find direct adaptive advantages, often by purely speculative argument, for nearly every widespread feature.

  Wells’s theme of “nonadaptive consequences” has been reasserted of late in an atmosphere of renewed attention to developmental patterns and the integrity of organization (animals cannot be analyzed as an amalgam of independent parts). Wells’s treatment of color follows these recent criticisms.

  For selection, the usual argument would propose a human population with considerable variation in skin color among its members. People with dark skin would, on average, be more successful in raising offspring and, slowly but surely, skin color within the population would shift toward darker hues. In other words, evolutionary change occurs by competition among individuals within a population (the “struggle for existence”).

  Wells explicitly denies this usual form of selection by claiming that favorable variants cannot spread through large and stable populations. His argument is incorrect and based on a false view of heredity, then current, called blending inheritance—the idea that all favorable variants will be diluted by half in offspring through intermarriage with a normal member of the population. The diluted offspring will then usually marry a normal individual (since favorable variants are so rare) and the subsequent generation will be diluted to one-quarter. Soon, the rare and favorable variant will be entirely swamped out. Heredity doesn’t work this way (although Wells couldn’t know what Mendel would discover fifty years later). Favorable traits often arise by mutation, and such features cannot be diluted by breeding with normal individuals. The mutation (if recessive) may not be expressed in the next generation, but it will not be eliminated. Wells’s belief in blending inheritance led him to deny selection by slow transformation within a population:

  Those varieties [that is, favorable variations], for the most part, quickly disappear, from the intermarriages of different families. Thus, if a very tall man be produced, he very commonly marries a woman much less than himself, and their progeny scarcely differs in size from their countrymen.

  How then can selection work? Wells argues that favorable variants can spread, presumably by chance rather than by selection (although he is not explicit), through small and mobile populations where vast numbers of normal individuals cannot impose dilution by backbreeding:

  In districts, however, of very small extent, and having little intercourse with other countries, an accidental difference in the appearance of the inhabitants will often descend to their late posterity.

  Thus, Wells conjectures that the people of Africa were initially divided into tiny, noninteracting populations. By chance, different average colors (and accompanying resistances to disease) became established among these populations. Selection then acted by competition between populations already different (for reasons unrelated to natural selection) in average skin color. Within each group, color was relatively constant and selection could only operate by sorting the groups themselves. Selection, in other words, occurs between groups, not among individuals within a group.

  Of the accidental varieties of man [meaning populations this time; Wells and his contemporaries used the word variety both for distinct individuals and for different populations], which would occur among the first few and scattered inhabitants of the middle regions of Africa, some one would be better fitted than the others to bear the diseases of the country. This race would consequently multiply, while the others would decrease, not only from their inability to sustain the attacks of disease, but from their incapacity of contending with their more vigorous neighbors. The color of this vigorous race I take for granted, from what has been already said, would be dark.

  The locus or level of selection is a “hot topic” within evolutionary theory today. While no one denies that selection works powerfully at the traditional level of differences among organisms within a population, other modes may also be important. The idea that selection may operate primarily among local populations—so-called intergroup selection—has long been advocated by the great geneticist Sewall Wright (who still argues eloquently for his position at age 95). Wright’s eclipse within strict Darwinian circles has recently been reversed and intergroup selection is now receiving a more favorable second look. I find it intriguing that the first formulation of natural selection advocated an intergroup process rather than the traditional focus on competing organisms.

  Nonetheless, although Wells’s argument was unorthodox by later Darwinian standards, it surely states the principle of natural selection. We must therefore return to our initial question. Why were these Darwinian harbingers totally ignored, and why does Darwin deserve his status (and, I fear, W
ells and Matthew theirs as well).

  Loren Eiseley makes the astute point (in Darwin’s Century) that Wells’s argument, as stated, cannot be extended or generalized to yield the panoply of evolutionary change through life’s history. Everyone knew that organisms varied and that local breeds could be manufactured from this raw material (how else did dog and pigeon fanciers work, not to mention farmers). But variation among breeds of dogs does not automatically extrapolate to the transformation from fish to human. Perhaps species have fixed and God-given limits of variation. We may make new breeds by selecting for extremes within these limits, but we cannot transcend the boundary to construct fundamentally new creatures. Wells does not generalize his argument to encompass large-scale evolutionary change, and hindsight alone may permit us to read his speculations as harbingers to Darwin’s overturn of biology.

  Still, Wells’s failure to generalize cannot be the main reason for his obscurity. (Darwin, by the way, only learned of Wells’s work from an American correspondent with antiquarian bibliographic interests.) The primary rationale is uncomplex. Ideas are cheap; mere statement counts for little or nothing. Intellectual fame accrues to people with the vision to make a good idea work in two ways: by using it to make new discoveries and by recognizing its implications as a far-ranging instrument for transforming general attitudes.

  We have no reason to suspect that either Wells or Matthew recognized any of the revolutionary power behind his cleverness. Wells presented natural selection as an appendage to an essay he didn’t even bother to publish until he lay dying. Matthew buried it among his trees and saw no forest (although he, unlike Wells, did advocate evolution as the cause of life’s history). Indeed, in a second letter responding to Darwin’s apology in 1860, Matthew damns Darwin with faint praise (and inadvertently condemns himself) by arguing that he never made much of selection because, unlike Darwin who struggled so hard to formulate the principle, he had grasped it as an evident deduction from the nature of things. He regarded it as necessarily true, almost trivial in that sense, and thus unworthy of much development. Matthew therefore missed all its significance:

  To me the conception of this law of Nature came intuitively as a self-evident fact, almost without an effort of concentrated thought. Mr. Darwin here seems to have more merit in the discovery than I have had—to me it did not appear a discovery. He seems to have worked it out by inductive reason, slowly and with due caution to have made his way synthetically from fact to fact onwards; while with me it was by a general glance at the scheme of Nature that I estimated this select production of species as an a priori recognizable fact—an axiom, requiring only to be pointed out to be admitted by unprejudiced minds of sufficient grasp.

  Darwin, on the other hand, used natural selection as the intellectual fulcrum of an entire career. He interpreted human evolution in its light, reformulated the principles of psychology, and explained the coevolution of orchids and their pollinating insects, the biogeographic distribution of organisms, the habits and actions of worms—a rich panoply of issues from the largest enigmas of life to the smallest quirks of particular organisms. He established a workable research program for an entire profession.

  I have found no documents of human thought more exciting than the notebooks that Darwin filled in London as a young man in his late twenties, just returned from five years aboard the Beagle. He had the key to a new view of life, and he knew it. His mind ranged over the entire intellectual landscape, from biology to psychology, morality, philosophy, and literature. Evolution by natural selection impinged on everything. Wells and Matthew had stated the same principle, but they had then either forgotten or had failed to draw any implications. Darwin sat in London, a young man rebuilding a world of thought. Consider but one statement, as a symbol of his achievement and a fitting end to this essay. Charles Darwin, cutting through two thousand years of tradition in Western philosophy with one epigrammatic note to himself:

  Plato says in Phaedo that our “imaginary ideas” arise from the preexistence of the soul, are not derivable from experience—read monkeys for preexistence.

  23 | Darwin at Sea—and the Virtues of Port

  CHARLES DARWIN AND ABRAHAM LINCOLN were born on the same day—February 12, 1809. They are also linked in another curious way—for both must simultaneously play, and for similar reasons, the role of man and legend. In a nation too young for mythic heroes, flesh and blood must substitute. Hence schoolchildren learn about Honest Abe, who freed the slaves single-handedly for simple justice, and who, as a young man, trudged for miles to return a few cents to a woman he had inadvertently short-changed. This legendary Lincoln may fulfill a national or psychological need, but historians must also labor to rescue the real, and wondrously complex, man from such a factually inaccurate role. Similarly, science worships no gods, and ancient sages are in strictly short supply. Historical figures must again form the stuff of needed legends. The apple beans Newton; Galileo drops his missiles from the Leaning Tower; and Darwin, alone at sea, transforms the intellectual world in splendid mental isolation.

  The myth of the Beagle—that Darwin became an evolutionist by simple, unbiased observation of an entire world laid out before him during a five-year voyage around the world—fits all our romantic criteria for the best of legends: a young man, freed from the trammels of English society and its constraining presuppositions, face to face with nature, parrying his fresh and formidable mind with all the challenges provided by plants, animals, and rocks throughout the globe. He leaves England in 1831, planning to become a country parson upon his return. He returns in 1836, having seen evolution in the raw, understanding (albeit dimly) its implications and committed to a scientific life as evolutionary thinker. The chief catalyst: the Galápagos Islands. The main actors: tortoises, mockingbirds, and above all, thirteen species of Darwin’s finches—the finest evolutionary laboratory offered to us by nature.

  We may need simple and heroic legends for that peculiar genre of literature known as the textbook. But historians must also labor to rescue human beings from their legends in science—if only so that we may understand the process of scientific thought aright. Darwin, to begin, did not become an evolutionist until several months after his return to London—probably not until March 1837 (the Beagle docked in October 1836). He did not appreciate the evolutionary significance of the Galápagos while he was there, and he originally misunderstood the finches so thoroughly that he was barely able to reconstruct the story later from his sadly inadequate records. The legend of the finches may persist, but it has been splendidly debunked in two recent articles by historian of science Frank Sulloway. His arguments form the basis of this essay (see bibliography).

  The thirteen species of Darwin’s finches form a closely knit genealogical group of widely divergent life styles—a classic case of adaptive radiation into a series of roles and niches that would be filled by members of several bird families in more conventional, and crowded, continental situations. We get our major clues about the adaptations of these species from the shapes of their bills. Three species of ground finches have large, medium, and small beaks, while a fourth grows a sharp, pointed bill. All are adapted to eating differing seeds of appropriate size and hardness. Two species feed on cactus and another on mangroves. Four inhabit trees—of these, one is a vegetarian, while the other three eat large, medium, and small insects, respectively. A twelfth species closely resembles warblers in form and habits; while the thirteenth, the most curious of all, uses twigs and cactus spines as tools to extract insects from crevices in tree trunks.

  The fine work of the great British ornithologist David Lack has taught us that the thirteen species evolved and became more distinct through a four-stage process of colonization, isolation and speciation, reinvasion, and perfecting of adaptation in competition. Lack also gave the birds their felicitous name of “Darwin’s finches,” in his 1947 book of the same title. But, contrary to anachronistic legend, this classic description of speciation is not a story that Darwin ever knew.r />
  Darwin visited the Galápagos in September and October 1835, landing on only four of the islands. At sea, sometime during the middle of 1836, he penned a famous statement in his Ornithological Notes, a major source for the legend that his Galápagos experiences directly converted him to evolution and that the finches inspired his new view of life:

  When I recollect, the fact from the form of the body, shape of scales and general size, the Spaniards can at once pronounce, from which Island any Tortoise may have been brought. When I see these Islands in sight of each other, and possessed of but a scanty stock of animals, tenanted by these birds, but slightly differing in structure and filling the same place in Nature, I must suspect that they are only varieties. The only fact of a similar kind of which I am aware, is the constant asserted difference—between the wolf-like Fox of East and West Falkland Islds.—If there is the slightest foundation for these remarks the zoology of Archipelagos will be well worth examining; for such facts would undermine the stability of Species.

  First of all, the “birds” of this passage are Galápagos mockingbirds, not finches. Darwin did notice that three of the four islands he visited contained distinctly different mockingbirds. At face value, this statement seems to display a strong preference for evolution; it certainly raises the possibility. But a familiarity with nineteenth-century zoological terminology suggests an alternate interpretation. All creationists admitted that species often differentiated into mildly distinct forms in situations, as on island chains and archipelagoes, where populations could become isolated in differing circumstances of ecology and climate. These local races were called varieties, and they did not threaten the created and immutable character of a species’ essence. Properly translated from the terminology of his time, Darwin says in this famous statement that either the tortoises and mockingbirds are merely varieties—in which case they do not threaten his creationist views—or they have become separate species, in which case they do. He briefly considered evolution by admitting the second possibility, but he ultimately drew back while still at sea by tentatively deciding (incorrectly, for the mockingbirds at least) that the island forms were only varieties. Darwin’s memories as an old man confirm this view that he only briefly flirted with, and then rejected, evolution while on the Beagle. He wrote to the German naturalist Otto Zacharias in 1877: “When I was on board the Beagle I believed in the permanence of species, but, as far as I can remember, vague doubts occasionally flitted across my mind.”