Bully for Brontosaurus

by Stephen Jay Gould

  Natural history does not share this consensus that individual units with particular legacies cannot shape the behavior and future state of entire systems. Our profession, although part of mainstream science since Aristotle, grants to individuals the potential for such a formative role. In this sense, we are truly historians by practice and we demonstrate the futility of disciplinary barriers between science and the humanities. We should be exploring our marked overlaps in explanatory procedures, not sniping at each other behind walls of definitional purity.

  Natural history stands in the crossfire and should provoke a truce by reaching in both directions. Individual organisms can certainly set the local history of populations and may even shape the fate of species. Walter the Walrus and Sarah the Squirrel are friendly and congenial, rather than risible, concepts (and may be actual creatures at the municipal zoo). Two recent cases of extraordinary (although not particularly likable) individuals have led me to consider this theme and to grant more attention to the vagaries of one in my profession.

  1. Jane Goodall’s quarter century with the chimpanzees of Gombe will rank forever as one of the great achievements in scientific dedication combined with stunning results. With such unprecedented, long-term knowledge of daily history, Goodall can specify (and quantify) the major determinants of her population’s fate. Contrary to our intuitions and expectations, the demography of the Gombe chimps has not been set primarily by daily rhythms of birth, feeding, sex, and death, but by three “rare events” (Goodall’s words), all involving mayhem or misfortune: a polio epidemic, a carnage of one sub-band by another, and the following tale of one peculiar individual.

  With odd and unintended appropriateness as we shall see, for the word means “suffering,” Goodall named one of the Gombe females Passion. Goodall met Passion in 1961 at the outset of her studies. In 1965, Passion gave birth to a daughter, Pom, and, as Goodall remarks (all quotes from The Chimpanzees of Gombe, Harvard University Press, 1986), “thereby gave us the opportunity to observe some extraordinarily inefficient and indifferent maternal behavior.”

  Nonetheless, Pom and Passion formed a “close, cooperative bond” as the daughter matured. In 1975, Passion began to kill and eat newborn babies of other females in her band. She could not easily wrest a baby from its mother and failed when acting solo, but Passion and Pom together formed an efficient killing duo. (Goodall observed three other “cannibalistic events” during nearly thirty years of work, all directed by males toward older chimps of other bands; Passion’s depredations are the only recorded incidents of cannibalism within a band.) During a four-year period, Passion and Pom, in sight of observers, killed and ate three infants by seizing them from their mothers and biting through the skull bones (sorry, but nature isn’t always pretty, and I hate euphemisms). They may have been responsible for the deaths of seven other infants. During this entire period, only one female successfully raised a baby. In studying Goodall’s curves of Gombe demography, the depredations of Passion have as great an impact as any general force of climate or disease. Moreover, the effects are not confined to the short years of Passion’s odd obsession (for reasons unknown, she stopped killing babies in 1977), but propagate well down the line. Since only one female was raising a baby in 1977, nearly all were in estrus, thus prompting a baby boomlet and sharp rise in population when Passion stopped her cannibalism.

  Such observational work on the behavior of animals in their natural habitat requires a personal pledge to maximal noninterference. Passion taxed this principle to its absolute limit. Goodall told me that when Passion died “of an unknown wasting disease” in 1982, she (Jane, not Passion) watched with renewed faith in noninterference and some legitimate sense of moral retribution.

  2. Notornis, the New Zealand ornithological journal, does not show up in the scientific equivalent of the corner drug store; I was therefore delighted when Jared Diamond alerted me (via Nature, which does appear at our watering holes) to a fascinating article by Michael Taborsky entitled “Kiwis and Dog Predation: Observations in Waitangi State Forest” (see the bibliography). The Waitangi Forest houses the largest “known and counted” population of the brown kiwi Apteryx australis—some 800 to 1,000 birds. In June and July of 1987, Taborsky and colleagues tagged twenty-four birds with radio transmitters “so that their spacing and reproductive activities could be studied” (all quotations come from Taborsky’s paper cited above).

  On August 24, they found a dead female, evidently killed by a dog. Thus began a tale worthy of The Hound of the Baskervilles. By September 27, thirteen of the tagged birds had been killed. All showed extensive bruising, and most had defeathered areas; ten of the thirteen birds “were found partly covered or completely buried under leaf litter and soil.” Scientists and forestry workers found ten more carcasses without transmitters, all killed and buried in the same way, and all dispatched during the same period.

  It didn’t take the sleuthing genius of Mr. Holmes to recognize that a single dog had wreaked this reign of terror. Distinctive footprints of the same form appeared by the carcasses, along with “dog droppings of one type and size.” On September 30, a female German shepherd, wearing a collar but unregistered, was shot in the forest. Her “long claws suggested that she had not been on hard surfaces for some time, i.e., was probably living in the forest.” The killings abruptly stopped. Taborsky tagged several more birds with transmitters, bringing the total to eighteen; all these birds survived to the end of the study on October 31.

  This Rin Tin Tin of the Dark Side had killed more than half of the tagged birds in six weeks. As “there is no reason to believe that birds with transmitters were at greater risk than those without,” the total killed may range to 500 of the 800 to 1,000 birds in the population. Lest this seem a staggering and unbelievable estimate, Taborsky provides the following eminently reasonable defenses. First, given the remote chance of finding a buried, untagged kiwi carcass, the ten actually located during the interval of killing must represent the tiny pinnacle of a large iceberg. Second, other evidence supports a dramatic fall in total population: Taborsky and colleagues noted a major drop in calling rates for these ordinarily noisy birds; a dog trained to find, but not to kill, kiwis could not locate a single live individual (although she found two carcasses) in a formerly well-inhabited section of the forest. Third, kiwis, having evolved without natural enemies and possessing no means of escape, could not be easier prey. Taborsky writes:

  Could a single dog really do so much damage? People working trained kiwi dogs at night know it is very easy indeed for a dog to spot and catch a kiwi. The birds are noisy when going through the bush and their smell is very strong and distinctive. When a kiwi calls, a dog can easily pick up the direction from more than 100 m away. With a kiwi density as high as it was in Waitangi Forest a dog could perhaps catch 10–15 kiwis a night, and the killing persisted for at least 6 weeks.

  As to why a dog would kill so many animals “for sport,” or at least not for food, who knows? We do, however, understand enough to brand as romantic twaddle the common litany that “man alone kills for sport, other animals only for food or in defense.” The kiwi marauder of New Zealand may have set a new record for intensity of destruction, but she followed the killing pattern of many animals. In any case, she surely illustrated the power of individuals to alter the history of entire populations. Taborsky estimates that, given the extremely slow breeding of kiwis, “the population will probably need 10–20 years and a rigorous protection scheme to recover to previous densities.”

  These two stories may elicit both fascination and a frisson, but still strike some readers as unpersuasive regarding the role of individuals in science. To be sure, both Passion and the austral hell hound had a disturbing effect on their populations. But science is general pattern, not ephemeral perturbation. The Gombe chimps recovered in a few years, as a subsequent baby boom offset Passion’s depredations. On the crucial issue of scale, individuals still don’t set patterns in the fullness of time or the largeness of spa
ce. Predictability under nature’s laws takes over at an amplitude of scale and a degree of generality meriting the name “science.” I would offer three rebuttals to this argument.

  First, scale is a relative concept. Who can set the boundary between perturbations in systems too small to matter and long-term patterns of appropriate generality? Human evolution is a tiny twig among millions on the tree of earthly evolution. But do all the generalities of anthropology therefore count only as details outside the more ample scope of true science? Earthly evolution may be only one story of life among unknown cosmic billions; are all the laws of biology therefore nothing but peculiarities of one insignificant example?

  Second, small perturbations are not always reined in by laws of nature to bring systems back to a previous equilibrium. Perturbations, starting as tiny fluctuations wrought by individuals, can accumulate to profound and permanent alterations in much larger worlds. Much of the present fascination for chaos theory in mathematics stems from its attempt to model such agents of pattern, even in large systems operating under deterministic laws. The Gombe chimps may feel no long-term effect of Passion’s cannibalism, but the Waitangi kiwis may never recover.

  Third, some natural populations may be so small that individuality dominates over pattern even if a larger system might fall under predictable law. If I am flipping a coin 10,000 times in a row, with nothing staked on any particular toss, then an individual flip neither has much effect in itself nor influences the final outcome to any marked degree. But if I am flipping one coin once to start a football game, then a great deal rides on the unpredictability of an individual event. Some important populations in nature are closer in number to the single toss than to the long sequence. Yet we cannot deny them entry into the domain of science.

  Consider the large, orbiting objects of our solar system—nine planets and a few score moons. The domain of celestial mechanics has long been viewed as the primal realm of lawfulness and predictability in science—the bailiwick of Newton and Kepler, Copernicus and Galileo, inverse square laws and eclipses charted to the second. We used to view the objects themselves, planets and moons, in much the same light—as regular bodies formed under a few determining conditions. Know composition, size, distance from the sun, and most of the rest follows.

  As I write this essay, Voyager 2 has just left the vicinity of Neptune and ventured beyond the planetary realm of our solar system—its “grand tour” complete after twelve years and the most colossal Baedecker in history: Jupiter, Saturn, Uranus, and Neptune. Scientists in charge have issued quite appropriate statements of humility, centered upon the surprises conveyed by stunning photographs of outer planets and their moons. I admit to the enormous mystery surrounding so many puzzling features—the whirling storms of Neptune, when the closer and larger Uranus appears so featureless; the diverse and complex terrain of Uranus’s innermost moon, Miranda (see the preceding essay). But I do think that a generality has emerged from this confusing jumble of diverse results, so many still defying interpretation—a unifying principle usually missed in public reports because it falls outside the scope of stereotypical science.

  I offer, as the most important lesson from Voyager, the principle of individuality for moons and planets. This contention should elicit no call for despair or surrender of science to the domain of narrative. We anticipated greater regularity, but have learned that the surfaces of planets and moons cannot be predicted from a few general rules. To understand planetary surfaces, we must learn the particular history of each body as an individual object—the story of collisions and catastrophes, more than steady accumulations; in other words, its unpredictable single jolts more than daily operations under nature’s laws.

  While Voyager recedes ever farther on its arc to the stars, we have made a conceptual full circle. When we launched Voyager in 1977, we mounted a copper disk on its side, with a stylus, cartridge, and instructions for playing. On this first celestial record, we placed the diversity of the earth’s people. We sent greetings in fifty-five languages, and even added some whale song for ecumenical breadth. This babble of individuality was supposed to encounter, at least within our solar system, a regular set of worlds shaped by a few predictable forces. But the planets and moons have now spoken back to Voyager with all the riotous diversity of that unplayed record. The solar system is a domain of individuality by my third argument for small populations composed of distinctive objects. And science—that wonderfully diverse enterprise with methods attuned to resolve both the lawful millions and the unitary movers and shakers—has been made all the richer.

  This is my third and last essay on Voyager. The first, which shall be my eternal incubus, praised the limited and lawful regularity that Voyager would presumably discover on planetary surfaces throughout the solar system. I argued, following the standard “line” at the time (but bowing to convention is never a good excuse), that simple rules of size and composition would set planetary surfaces. With sufficient density of rocky composition, size alone should reign. Small bodies, with their high ratios of surface to volume, are cold and dead—for they lose so much internal heat through their relatively large surface and are too small to hold an atmosphere. Hence, they experience no internal forces of volcanism and plate tectonics and no external forces of atmospheric erosion. In consequence, small planets and moons should be pristine worlds studded with ancient impact craters neither eroded nor recycled during billions of years. Large bodies, on the other hand, maintain atmospheres and internal heat machines. Their early craters should be obliterated, and their surfaces, like our earth’s, should bear the marks of continuous, gentler action.

  The first data from planetary probes followed these expectations splendidly. Small Mercury and smaller Phobos and Deimos (the moons of Mars) are intensely cratered, while Mars, at its intermediary size, showed a lovely mixture of ancient craters and regions more recently shaped by erosion and volcanic action. But then Voyager reached Jupiter and the story started to unravel in favor of individuality granted by distinctive histories for each object.

  Io, Jupiter’s innermost major moon, should have been dead and cratered at its size, but Voyager spotted large volcanoes spewing forth plumes of sulfur instead. Saturn’s amazingly complex rings told a story of repeated collisions and dismemberments. Miranda, innermost moon of Uranus, delivered the coup de grâce to a dying theory. Miranda should be yet another placid body, taking its lumps in the form of craters and wearing the scars forever. Instead, Voyager photographed more signs of varied activity than any other body had displayed—a geological potpourri of features, suggesting that Miranda had been broken apart and reaggregated, perhaps more than once. Brave new world indeed.

  I threw in the towel and wrote my second essay in the mea culpa mode (reprinted as the preceding essay). Now I cement my conversion. Voyager has just passed Neptune, last post of the grand tour, and fired a glorious parting shot for individuality. We knew that Triton, Neptune’s largest moon, was odd in one important sense. All other bodies, planets around the sun and moons around the planets, revolve in the same direction—counterclockwise as you look down upon the plane of the solar system from above.* But Triton moves around Neptune in a clockwise direction. Still, at a size smaller than our moon, it should have been another of those dead and cratered worlds now mocked by the actual diversity of our solar system. Triton—and what a finale—is, if anything, even more diverse, active, and interesting than Miranda. Voyager photographed some craters, but also a complexly cracked and crumpled surface and, most unexpectedly of all, volcanoes, probably spewing forth nitrogen in streaks over the surface of Triton.

  In short, too few bodies, too many possible histories. The planets and moons are not a repetitive suite, formed under a few simple laws of nature. They are individual bodies with complex histories. And their major features are set by unique events—mostly catastrophic—that shape their surfaces as Passion decimated the Gombe chimps or the austral hound wreaked havoc on the kiwis of Waitangi. Planets are like orga
nisms, not water molecules; they have irreducible personalities built by history. They are objects in the domain of a grand enterprise—natural history—that unites both styles of science in its ancient and still felicitous name.

  As Voyager has increased our knowledge, and at least for this paleontologist, integrated his two childhood loves of astronomy and fossils on the common ground of natural history, I cannot let this primary scientific triumph of our generation pass from our solar system (and these essays) without an additional comment in parting.

  Knowledge and wonder are the dyad of our worthy lives as intellectual beings. Voyager did wonders for our knowledge, but performed just as mightily in the service of wonder—and the two elements are complementary, not independent or opposed. The thought fills me with awe—a mechanical contraption that could fit in the back of a pickup truck, traveling through space for twelve years, dodging around four giant bodies and their associated moons, and finally sending exquisite photos across more than four light-hours of space from the farthest planet in our solar system. (Pluto, although usually beyond Neptune, rides a highly eccentric orbit about the sun. It is now, and will be until 1999, within the orbit of Neptune and will not regain its status as outermost until the millennium. The point may seem a bit forced, but symbols matter and Neptune is now most distant. Moments and individualities count.)

  The photos fill me with joy for their fierce beauty. To see the most distant moon with the detailed clarity of an object shot at ten palpable paces; the abstract swirling colors in Jupiter’s great spot; the luminosity and order of Saturn’s rings; the giant ripple-crater of Callisto, the cracks of Ganymede, the sulfur basins of Io, the craters of Mimas, the volcanoes of Triton. As Voyager passed Neptune, her programmers made a courtly and proper bow to aesthetics and took the most gorgeous picture of all, for beauty’s sake—a photograph of Neptune as a large crescent, with Triton as a smaller crescent at its side. Two horns, proudly independent but locked in a common system. Future advertisers and poster makers may turn this exquisite object into a commercial cliché, but let it stand for now as a symbol for the fusion of knowledge and wonder.