The Song of The Dodo, page 49
MacArthur felt that the science of ecosystems should venture beyond description. It shouldn’t limit itself to collecting and indexing facts. It should find broader patterns in the natural world, and from those patterns it should extract general principles. It should measure and count and perform calculational abstractions that would illuminate the essential amid the contingent. It should construct mathematical models that would function as usefully as a slide rule. It should be vigorous enough and bold enough to make predictions. It should offer theory. Olof Arrhenius, Henry Allan Gleason, and a few other ecological researchers had made modest efforts in that vein. So had Hutchinson himself. And Frank Preston had begun ringing the bell of canonical distribution just as MacArthur reached his scientific adulthood. But ecology as generally practiced was still a loose-jointed, descriptive, nonquantified, nontheoretical enterprise.
MacArthur began to teach. He continued to publish interesting papers. His reputation blossomed. In 1965, after several years at the University of Pennsylvania, he accepted a professorship at Princeton, his role there to include the overall editorship of the Monographs in Population Biology, which offered promise as a forum for the newfangled ecology that he favored. MacArthur would co-author the first monograph himself. By that time he had met and begun sharing ideas with another young scientist, Edward O. Wilson.
Wilson was a myrmecologist, a specialist on the biology of ants. He had grown up in the South, a nature-loving boy who collected insects and kept snakes, spending much of his time alone in the woods and swamps of Alabama and northern Florida. He had become interested in ants by the time he was nine, and soon after that he began doing precociously serious myrmecological fieldwork. Why ants? To some degree it was their inherent fascination, to some degree it was a choice urged by necessity. “I had use of only my left eye,” Wilson explains in an autobiographical essay published in midcareer. The right eye “was mostly blinded by a traumatic cataract when I carelessly jerked a fish fin into it at the age of seven.” With only monocular vision, he had found it hard to watch birds or mammals in the field. But the left eye was very acute, especially for fine detail at close range. “I am the last to spot a hawk sitting in a tree, but I can examine the hairs and contours of an insect’s body without the aid of a magnifying glass.” Many young boys collect insects; this one-eyed boy was doing real science.
At age thirteen Edward Wilson began a rigorous study of certain ant groups in the Mobile area and made his first publishable observation. Several years later, with adolescent earnestness, he decided that he should pick an entomological specialty. Based on the challenge and opportunity they offered, he chose flies (the order Diptera), in preference to ants. But it was 1945 then, and World War II had interrupted the supply of insect pins, which came mainly from Czechoslovakia. Since ants are best preserved in small vials of alcohol rather than mounted on pins, Wilson switched back to them—and has never regretted it. “In a sense, the ants gave me everything,” he declares. His highest career aspiration at that age was to be a government entomologist, “to ride around in one of those green pickup trucks used by the U.S. Department of Agriculture’s extension service” and help farmers cope with their crop pests. But he had a first-class scientific brain, as it turned out, which carried him from the University of Alabama to the University of Tennessee and then to Harvard. The particular attraction of Harvard, as put to him, was that its museum held the world’s largest collection of ants. “Get a global view,” an older colleague had told him; “don’t sell yourself short with entirely local studies.” When he met Robert MacArthur, in late 1959, Wilson had recently returned from a long stint of fieldwork in the tropics.
His skills and his interests were complementary to MacArthur’s. Whereas MacArthur had shifted from mathematics to mathematical ecology, Wilson was a taxonomist and a zoogeographer. He had made extensive collections in New Guinea and Australia, on the island of New Caledonia, in the New Hebrides, on Fiji. He knew more about the Cerapachyinae and the Ponerinae subfamilies of ants in Melanesia than any man-jack on Earth—what they looked like, how they made their livings, which species lived on which islands. Like MacArthur, though, he was interested in more than the description of naturalhistory phenomena. As his head and his field notebooks filled with ant data, Wilson had begun to see patterns. For example: The number of ant species on an island tended to correlate closely with island size.
Wilson’s brainload of purely descriptive data seems to have helped bring on an existential headache. In 1961, feeling mildly depressed and unsure about his professional direction, he took a sabbatical. During this getaway from Harvard he went to South America. He loved fieldwork as much as ever, and the rainforests of Surinam, to his great pleasure, were rife with previously unstudied ants. He also visited the islands of Trinidad and Tobago, just offshore from Venezuela. Trinidad is large, Tobago is small. On Trinidad he found more species of ant than on Tobago.
Pondering the descriptive sort of work he had been doing, Wilson yearned for something more. “It just didn’t seem enough to continue enlarging the natural history and biogeography of ants,” he confides in his short memoir. “The challenges were not commensurate to the forces then moving and shaking the biological sciences.” His recent acquaintance with Robert MacArthur and some other young mathematical ecologists, and his awareness of G. Evelyn Hutchinson’s work, had persuaded Wilson that “much of the whole range of population biology was ripe for synthesis and rapid advance in experimental research; but this could only be accomplished with the aid of imaginative logical reasoning strengthened by mathematical models.” He was a mediocre mathematician, by his account, with no training beyond algebra and statistics. So during his brooding summer in Trinidad and Tobago, besides collecting ants, he taught himself some calculus and probability theory out of textbooks. Returning to Harvard, he enrolled in a mathematics class and sat conscientiously, as an associate professor, in a small desk among a crowd of undergrads. Eventually, after further remedial classes, he had enough math to feel comfortable. Meanwhile he began a collaboration that would take him beyond the descriptive.
“In 1962 Robert H. MacArthur and I, both in our early thirties, decided to try something new in biogeography,” Wilson relates. “The discipline, which studies the distribution of plants and animals around the world, was ideal for theoretical research. Biogeography was intellectually important, replete with poorly organized information, underpopulated, and almost devoid of quantitative models. Its borders with ecology and genetics, specialties in which we also felt well prepared, were blank swaths across the map.” Wilson told MacArthur that he thought biogeography could be made into a rigorous, analytical science.
There were striking regularities in the welter of data, Wilson said, that no one had explained. The species-area relationship, for instance. More particularly, the recurrent ratio to which Philip Darlington had called attention: With each tenfold decrease in area came roughly a twofold decrease in species diversity. Among the ant species of Asia and the Pacific islands Wilson had noticed another pattern. Newly evolved species seemed to originate on the large landmasses of Asia and Australia and to disperse adventurously from there out to the farflung islands. As those dispersing species colonized small and remote places such as Fiji, they seemed to supplant the older native species that had gotten there before them. New species were continually arriving, old species were continually going extinct, and the net effect was… no gain or loss in number of ant species. It looked to Wilson like some sort of natural balance.
Yes, said MacArthur, an equilibrium.
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“HE WAS MEDIUM tall and thin, with a handsomely angular face,” as Wilson remembers MacArthur. This was written a decade after MacArthur’s early death. “He met you with a level gaze supported by an ironic smile and widening of eyes. He spoke with a thin baritone voice in complete sentences and paragraphs, signaling his more important utterances by tilting his face slightly upward and swallowing.” Although it may not have been a complete sentence when MacArthur first spoke the word “equilibrium” to Wilson, presumably he tilted up his face.
“He had a calm understated manner,” Wilson continues, “which in intellectuals suggests tightly reined power. Because very few professional academics can keep their mouths shut long enough to be sure about anything, MacArthur’s restraint gave his conversation an edge of finality he did not intend. In fact he was basically shy and reticent.”
To that portrait, subjective and affectionate, Wilson adds a statement that stands as dead accurate: “By general agreement MacArthur was the most important ecologist of his generation.”
The two of them brainstormed together during 1961 and 1962 over this notion of a biogeographical balance. They scrutinized Wilson’s ant data from Melanesia. They looked at patterns of distribution among bird species in the Philippines, Indonesia, and New Guinea, which they extracted from published work by Ernst Mayr and others. They referred back to Darlington’s enumeration of beetle and reptile species on the various Antillean islands, and they looked into the case of Krakatau, for which there were those historical records of recolonization by animal species after the cataclysmic purge. They read Frank Preston’s recent paper on the canonical distribution of commonness and rarity, finding it essentially in agreement with their own views. They grew convinced that the species lost from an island, during a given span of time under ordinary circumstances, are roughly equal in number to the species gained by the same island over the same span of time. Unless the island itself is very recent in origin or has undergone a sudden disruption, the rates of losses and gains tend to cancel each other out. The result is a dynamic stability. The number of resident species remains steady while, with one species replacing another, the roster of identities changes continually.
Just how are species lost from an island? By local extinction. And how are they gained? Two ways: (1) by speciation, when a single old species splits into a pair of new species, and (2) by immigration, when a species arrives and becomes established. MacArthur and Wilson suspected that the second of those two, immigration, is vastly more frequent than the first. Speciation could be disregarded, then, and the equilibrium they envisioned could be expressed as a balance between immigration and extinction. It’s worth repeating that extinction in this context refers usually to the local extinction of a population, not to the global extinction of a species. Mainlands or neighboring islands, having supplied the flow of transoceanic immigrants, supply still more as extinctions occur.
MacArthur and Wilson drew a simple, vivid graph that showed two sloping lines forming an X: the immigration line coming down, from left to right, and the extinction line going up. The downward slope indicated that immigration events tend to decrease in frequency as an island becomes crowded with species. The upward slope indicated the converse—that extinction events tend to increase in frequency with increasing crowdedness. Each of the lines was curved slightly, into a gentle concave sag, indicating subtle changes in the rate at which immigration decreases and extinction increases on an ever fuller island. In midgraph, the lines crossed; their crossing point marked equilibrium. The number of species corresponding to that graph point is the island’s normal complement of species, remaining roughly constant through time. At least that’s what MacArthur and Wilson hypothesized.
They also created an intricate mathematical model—a long sequence of differential equations capable of accepting numerical data at one end and, like the canning line in a pickle factory, emitting a conveniently transmogrified product at the other end. The product of this canning line was predictions. The model foretold particulars of equilibration (how much elapsed time? how many species?) on a given island.
MacArthur and Wilson then co-authored a paper, which the journal Evolution published in 1963. Titled “An Equilibrium Theory of Insular Zoogeography,” this paper contained the essence of their concept, lucidly presented, but for one reason or another it didn’t have the immediate effect of turning the whole science of ecology sideways. That was still to come.
They weren’t finished with the theory. They expanded the range of supporting data to include plant species as well as animals. They added some discussion of related topics—the process of colonization, the process through which an island community might resist colonization by new species, and also a bit about evolution on islands. Four years later, their expanded version became volume one of the Princeton monographs, published as The Theory of Island Biogeography. The slight change in title, from the article to the book, suggested a major increase in confidence and scope.
The new title even sounded a little presumptuous. An equilibrium theory of island biogeography had become the theory of island biogeography. It wasn’t actually the only such theory; the scientific literature was already lightly peppered with theoretical notions concerning the biogeography of islands. But none of the others was so forceful, none was so detailed, and none ever proved so influential. The title’s presumption was vindicated. This was the book that changed things.
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To SOME people, few but vocal, Edward O. Wilson is a bugbear, infamous as the leading enunciator of a branch of science called sociobiology. To others, he is famous and much admired for the same reason. Yes, it’s the same Edward O. Wilson who published Sociobiology: The New Synthesis in 1975, daring to suggest that human social behavior might be partly shaped by evolutionary genetics. That phase of his life and career is a story in itself (how he was accused of inventing pseudoscientific justification for a racist and sexist status quo; how he was denounced in print by leftist intellectuals and on the placards of angry young demonstrators; how he achieved the unwelcome distinction of having a pitcher of water dumped on his head, by one of those demonstrators, while addressing the American Association for the Advancement of Science), but it’s not the story I’m telling. To still other people, more recently, Edward O. Wilson is a brilliant polymath and an elegant writer, a statesmanlike voice of warning about global losses of biological diversity, a wise elder to the conservation movement. And among his entomological colleagues, he is a towering authority on the taxonomy and behavior of ants.
Aware of all those Wilson personae, I’m interested in still another. To me he’s the sole surviving member of the MacArthur-and-Wilson partnership, and therefore a maker of history. He’s the one living human best qualified to explain how such an informal and seemingly peripheral field as island biogeography became so formalized and so central to the science of ecology. He’s also, as I discover, a generous, mild, and unassuming man. He offers me three hours of intellectual hospitality from the middle of his busy workday as calmly as a goodhearted Methodist minister visiting the sick. “Please call me Ed,” he says. “And I’ll call you David, if I may.”
His office, on an upper floor of Harvard’s Museum of Comparative Zoology, is a large, cheerful room decorated in memorabilia and ants. Unlike the ants that come and go through my own office, his are in cages. The cages are neat plastic units arrayed on long lab tables. Some of them, no doubt the ones holding tropical species, are warmed gently by red electric bulbs. An oversized bronze sculpture of an ant, big as a lobster, sits on a pedestal bearing an award inscription. An old Georgia license plate, a nonsense memento of the sort that arrive in the mail as gifts, reads HIANTS. And the skull of a sabertooth cat (or a facsimile cast, anyway) rests on a table, offering a note of mammalian relief to the myrmecological theme.
Far up on the left wall hangs a row of imposing, black-framed photographs: five venerable men. Are they Ed Wilson’s distinguished predecessors here at the Museum of Comparative Zoology? That’s my guess; and I succeed in identifying one of those faces as William Morton Wheeler, a great American ant maven of the early twentieth century. The rest are strangers to me. Five dignified elders, they glower down on everything. Has the Harvard administration issued these photos as mandatory office decor, like the unctuous shot of the president in every post office? On the opposite wall, ironically contrapuntal in identical black frames, five ants glower back.
Far across the room, inconspicuous beside Wilson’s small desk, hangs another photo: the young Robert MacArthur.
Before we get serious about islands, Wilson hosts me to lunch. From his office refrigerator he pulls out turkey sandwiches, bottles of lingonberry juice, and paper-wrapped pieces of baklava, all of which he seems to have shopped for at some local deli himself. He apologizes, this eminent man, this wonderful lunatic of politeness, for the food’s not being fancy. But the turkey is fine and the lingonberry juice has come all the way from Finland. As we stuff our faces we talk ramblingly about the politics of scientific funding (especially ecology versus molecular biology, with ecology getting short shrift) and about the sociopolitical challenge of conserving biological diversity. Both those related subjects concern him deeply. But the Finnish juice gets us off on a digression about Scandinavian surnames, and he voices curiosity about mine.
It’s Norwegian, I answer. The original version, before Ellis Island—so I’ve been told, anyway—translates roughly as “cow-herder” or “cow-man.” I suppose that could be stretched to “cowboy,” if a person liked the ring of the word, which I don’t. Besides, I say, in Norway there’s no swaggering ethos involving horses and dip tobacco and pointy boots. My prattle on the subject moves Wilson to confide that he has always chafed at the ordinariness of his own name. If it had to be WASP, he says, at least it could have been something more robust. Such as Stonebreaker, he muses. Curling his mouth to a little smile, he stares into space and repeats, Stonebreaker. I imagine it: Dr. Edward O. Stonebreaker, the renowned ant expert and sociobiologist, announced today at Harvard that he would no longer use the name Wilson and that, furthermore, no Marxist yoyos would ever again dump water on HIS head.
