The Monkey's Voyage

by Alan de Queiroz

  Wegener began thinking about continental movement in 1910. He and a friend were browsing through a new atlas when Wegener noticed what Ortelius, Snider-Pelligrini, and others had before. “Please look at a map of the world!” he wrote to his fiancée. “Does not the east coast of South America fit exactly with the west coast of Africa as if they had formerly been joined?”6 In 1912, he published two papers on his new continental drift theory. When these papers were heavily criticized, Wegener’s father-in-law, a climatologist, warned him against jumping into a new field. By then, however, Wegener was committed to his theory, and, in any case, he wasn’t one to let the usual boundaries of academic disciplines hem him in. He knew that the theory was revolutionary and he felt an urgency to pursue it much further. “If it turns out that sense and meaning are now becoming evident in the whole history of the Earth’s development,” he wrote to his father-in-law, “why should we hesitate to toss the old views overboard? Why should this idea be held back for ten or even thirty years?” He would find out why, although the knowledge undoubtedly wouldn’t have stopped him.

  An obvious initial goal was to figure out how the continents had once been arranged. Gravity measurements and other evidence showed that continental crust was less dense than the crust of the ocean floor, which indicated to Wegener (and to many geologists of the time) that the rock underlying continents was a distinct and permanent feature of the Earth. If this was true—if the extent of continental crust had remained largely intact through time—it meant that landmasses that once had been broadly attached to each other should fit together like pieces of a puzzle; the solution could be found because all the pieces were still around. At first, Wegener simply used the coastlines as they are, but later he matched the outlines of the continental shelves, which more accurately reflect the borders of continental crust. What he found, with some fudging here and there, was an exceptionally good fit. It looked as though all the continents had once been part of a single supercontinent. Wegener called this enormous landmass the Urkontinent (the “original continent”), but it soon became known by a different name, one that we still use today—Pangea, Greek for “All-Earth.”

  If Pangea had really existed, then there should be evidence of it in the rocks. In particular, there should be geological features and fossils that were continuous across the various, now separated continents. If, for example, Africa and South America had been connected, one should find some of the same rock formations on both continents, and, when the two puzzle pieces were set against each other in their original positions, those formations should line up. Wegener likened the continents—the fragments of Pangea—to a torn newspaper; the lines of print would run evenly across the page if one put the pieces back together in their proper arrangement.

  Some of Wegener’s most compelling evidence came from matching up such “lines of print.” The lines came in many different forms, including mountain ranges, coal beds, sedimentary and volcanic rock formations, glacial deposits, and fossil occurrences. There are folded mountains in Scotland and Ireland that continue in Newfoundland. There are coal fields in Belgium and the British Isles aligned with coal fields in the Appalachians. There are matching volcanic kimberlite pipes containing white diamonds in Africa and South America. There are fossils of the so-called Glossopteris flora on all the southern continents, including Antarctica, and those of the freshwater reptile Mesosaurus in southern Africa and southern South America. There are glacial erratics “of a peculiar quartzite grit with banded jasper pebbles” that seem to have arisen in ancient mountains of Griqualand in southern Africa, but are also found in Brazil. Wegener wrote that finding so many matching “lines of print” argued a million to one in favor of continental movement. The million-to-one odds he pulled out of a hat, but the general argument was sound; if you arrange the pieces of a puzzle and twenty swaths of color run through it, all aligned, you’ve done the puzzle right.

  The theory also explained some strange observations about ancient climates, a particular interest of Wegener’s from his work as a meteorologist. Wegener focused on the Carboniferous and Permian periods, when parts of South America, India, Africa, and Australia show abundant evidence of an ice age while vast areas of North America, Europe, and Asia were covered by warm, wet forests. (The name “Carboniferous” comes from the coal beds that formed from the remains of the forest plants.) It seemed that parts of the world that are now warm had been cold, while, at the same time, parts that are now cold had been warm. Others had tried to explain this conundrum by moving, not the positions of the continents, but the locations of the poles. However, Wegener saw that there was no polar location that by itself adequately explained the climate pattern. One always ended up with anomalies, such as big glaciers near the Equator. Instead, he showed that the paradox could be explained by continental drift: with all the continents conglomerated into Pangea, and the South Pole positioned near the southern end of the supercontinent, the pattern of glaciation in the south and warm forests in the north made perfect sense.

  Wegener found himself more or less in the position of Darwin and Wallace when they had convinced themselves that evolution happened, but they hadn’t yet come up with natural selection as the mechanism. Wegener knew that continental drift occurred, but he didn’t know what caused it. In his book Die Entstehung der Kontinente und Ozeane (The Origin of Continents and Oceans), he threw in a couple of ideas, probably knowing that they weren’t right or, at least, weren’t enough. One was a centrifugal force generated by the spinning Earth that, by acting differently on continental crust and ocean crust, would supposedly push the continents toward the Equator. The second was the tidal force of the sun and moon pulling on the continents and sending them westward with respect to the ocean floor. In both cases, Wegener envisioned the continents pushing through the ocean crust, rock plowing through rock. That would turn out to be a big problem.

  His book appeared in German in 1915 (although it was not until the translation of a third edition in 1924 that it became available in English). The first edition was only ninety-four pages long, more like a novella than a novel, but it was monumental in scope. Later editions were even more impressive, as Wegener essentially rewrote the book for each edition, continuing to add new evidence. Reading it is a bit like reading The Origin of Species, in that one is constantly struck by how prescient and modern it is. Wegener talks of rift valleys as incipient oceans (which is what they are); of the clockwise rotation of landmasses bordering the Pacific (which is why Los Angeles and San Francisco are heading in opposite directions); and of connections between continental drift, faulting, earthquakes, and volcanoes (which are now all understood as linked phenomena).7 From the beginning, many scientists seemed to realize that this was a serious and potentially revolutionary piece of work, and the book was widely read and widely discussed. Conferences were held about it. Wegener was no Gregor Mendel, planting his peas in obscurity. The book almost immediately made him well known.

  You will often read that the ultimate outcome of all this attention was the rejection and ridicule of Wegener’s theory. Damning judgments from geologists and other scientists did come thick and fast. “Wegener’s hypothesis in general is of the foot-loose type, in that it takes considerable liberty with our globe, and is less bound by restrictions or tied down by awkward, ugly facts than most of its rival theories,” wrote one geologist. Another called Wegener’s theory “a beautiful dream, the dream of a poet. One tries to embrace it, and finds that he has in his arms but a little vapor or smoke.” A third was even more pointed, describing Wegener’s argument as “ending in a state of auto-intoxication in which the subjective idea comes to be considered an objective fact.” Jokes about continental drift also circulated in university classes. There was the one, for instance, about half of a fossil specimen from Europe matching perfectly with another half dug up in North America, like an amulet in a fairy tale.

  However, the notion that the reaction to Wegener’s views was almost totally n
egative is an oversimplification. It turns out that the response to the drift theory was very inconsistent from place to place. In Britain and, especially, continental Europe, many scientists saw the merit in at least some of Wegener’s arguments. Quite a few of them had seen the matching strata, landforms, or fossils on opposite sides of the Atlantic for themselves, and viewed those “lines of print” as strong evidence that the continents had been joined. Although relatively few European scientists became wholehearted supporters of continental drift, the seeds that Wegener planted there were not simply eradicated. The English geologists Fred Vine and Drummond Matthews, for example, both recalled being receptive to the drift theory well before they made their own discoveries about seafloor magnetic anomalies, findings that helped vindicate Wegener’s ideas.8

  It was in the United States that the reaction to Wegener closely matched the widely held story of rejection and ridicule. It was there that the drift theory was commonly seen as “foot-loose” and Wegener as “auto-intoxicated” by his own mental machinations. Critics especially attacked Wegener’s proposed mechanisms to account for continental movement; it just didn’t seem reasonable that continents could plow like giant barges through oceans of solid rock, and, in any case, the centrifugal and tidal forces that Wegener pointed to seemed totally insufficient for the task. These critics felt that, without a reasonable mechanism, the whole edifice of drift theory was fundamentally unsound. By proposing implausible (and, as it turns out, completely incorrect) mechanisms for continental movement, Wegener left himself open to attack. And it seems that many scientists threw out the baby—the fact of drift, regardless of mechanism—with the bathwater.

  However, this account fails to explain why Americans were so much more opposed to the theory than were their European (and European colonial) counterparts. Perhaps it would be more accurate to say that the lack of a reasonable mechanism was exploited by scientists who were strongly biased in the first place to reject Wegener’s arguments. Why Americans were especially biased is not an easy thing to answer. However, the historian of science Naomi Oreskes has suggested that American geologists were particularly enamored of new kinds of instruments and the hard numbers that came out of them (a kind of intoxication with technology that has bedeviled scientists of many sorts), and, consequently, that they tended to give little weight to what they viewed as old-fashioned, “subjective” evidence. In this view, the problem that Americans had with Wegener was that his evidence was almost all of this subjective type—things like the identity of landforms and strata in South America and Africa that were invariably based on the opinions of a few geologists.9 The Americans wanted numbers, and, as it turned out, those numbers would be a long time in coming.

  Despite these complications, it is reasonable to conclude that Wegener’s theory was not generally accepted, even in Europe. In hindsight, it does seem like an odd, if not completely inexplicable, episode in the history of science. One wonders, in particular, what was going on in the minds of the many scientists who took the trouble to read Wegener’s book, with its piles of evidence, and yet still thought he was utterly wrong. One also wonders how history might have been altered if only he had managed to convert a few more prominent geologists. But it didn’t happen. Perhaps, in the most general sense, it’s just that scientists have a hard time giving up their entrenched views. In most instances, that kind of conservatism probably makes sense—it keeps people from wasting their time chasing “vapor or smoke.” Occasionally, however, scientists have to break out of that conservatism, lest they be left in the dark.

  At the meeting of the Geological Society of America in 1922, a geologist named R. Thomas Chamberlin, harshly criticizing the drift theory, said, “If we are to believe Wegener’s hypothesis, we must forget everything which has been learned in the last 70 years and start all over again.”

  That was exactly right.

  In the spring of 1930, Wegener embarked on his fourth trip to Greenland, leading an expedition to make meteorological and ice measurements. From the start, the expedition was plagued by delays and equipment problems. In the fall, when two men stationed at an outpost in the middle of the icecap began to run out of supplies, Wegener decided to lead a group out from a camp on Greenland’s west coast to reprovision them. Often traveling through deep, fresh snow with their heavy dogsleds, it took the party forty days to reach the outpost, three times as long as it might have under ideal conditions. After resting for just two days at the outpost, Wegener and a companion, an Inuit named Rasmus Villumsen, headed back toward the west coast. The date was November 1, Wegener’s fiftieth birthday. A few things are known or can be inferred about their return journey. The extreme cold and howling winds must have slowed them down. They eventually abandoned one of the two dogsleds, and from that point Wegener traveled on skis while Villumsen rode the remaining sled.

  Six months later, a search party found Wegener buried near his upright skis, in a grave that Villumsen apparently had dug. His body was lying on a reindeer skin and a sleeping bag and was sewn up in two sleeping bag covers. There is a thought that he died of heart failure. Villumsen made it at least twelve miles farther, but then all trace of him disappeared. His body was never found.

  To some, Wegener’s death in Greenland might seem like an all-too-fitting end to the even greater tragedy of his life, defined by the fact that he had proposed a great scientific theory, but was maligned for it and never saw his idea vindicated. However, that view assumes that he was almost universally considered a crackpot, which, as described above, wasn’t actually the case. In fact, upon his death, the prominent scientific journal Nature ran a full-page obituary, calling his passing “a great loss to geophysical science.” In any case, the man who led the Greenland expedition does not come across as pitiful in any way. If he was weighed down by anything, it was worry over the logistics of a complex operation at the mercy of the weather, and concern for the safety of his men. The accounts of other expedition members make him out to be an intensely respected, if taciturn, leader, thoroughly focused on the job at hand.

  When Wegener’s body was found, his nose and hands were marked by frostbite, but his eyes were open, and, according to one member of the search party, “the expression on his face was calm and peaceful, almost smiling.” Perhaps there’s a personal metaphor in the image of Wegener in death: he was scarred by life, but remained unbroken.

  NEW YORK BEFORE THE STORM

  Wegener’s theory did not die with him, but at the time of his death it looked to be somewhat moribund. The drift theory did have a substantial minority of followers in continental Europe, but, in Britain, very few scientists thought Wegener was right, and in the United States, virtually none. His book had caused a great stir, but not the worldwide advance in geology—and biogeography—that it could have and should have created. A few scientists, notably the South African geologist Alexander du Toit, adamantly used Wegener’s theory to explain plant and animal distributions broken up by oceans, but they were in a small minority. In the terminology of the philosopher Thomas Kuhn, the “paradigm shift” didn’t happen, and “normal science” largely went on as before.

  Oddly enough, however, in 1915, the same year that Wegener’s book was published, a book-length paper came out that laid the foundation for a substantial change in biogeographic thinking that had nothing to do with continental drift. At that time, the land-bridge builders, intellectual descendants of Joseph Hooker (before Darwin converted him), had the upper hand over Darwinian dispersalists. The outlines of now-sunken connections were being drawn on maps willy-nilly wherever closely related species were found on both sides of a sea or ocean. There were, supposedly, bridges between South America and Africa, South America and Australia, Madagascar and India, Europe and North America, Samoa and Hawaii, and on and on (see Figure 1.3). Sometimes, as for the link between South America and Africa, several alternative bridges were hypothesized, none of them based on any reasonable geological evidence. In retrospect
, this episode of biogeographic history seems laughable, but there was a certain logic to it. Despite Darwin’s experiments, land-bridge enthusiasts simply could not believe that oceanic dispersal of terrestrial organisms was important, and, like most scientists at the time, they didn’t believe in continental drift. Former land bridges were a way out of the dilemma.

  1.3 Two of the many land bridges conjured up to explain plant and animal distributions. Redrawn and modified from Hallam (1994).

  The 1915 paper that began to swing the pendulum back was entitled “Climate and Evolution.”10 Its author was William Diller Matthew, a thin, bespectacled, professorial-looking fellow who worked at the American Museum of Natural History in New York City as a curator with a specialty in fossil mammals. When it came to explaining distributions broken up by oceans, Matthew was very much like Darwin. Both of them believed in the fixed positions of continents, and both were leery about invoking former land bridges without geological evidence. This meant that Matthew, like Darwin, was a dispersalist. Matthew didn’t think as much as Darwin did about seeds in seawater or snails clinging to duck feet, but that was because he was a mammalogist; most of his study organisms needed natural rafts to disperse across wide expanses of water.

  When it came to the frequency of dispersal events, Matthew’s argument was all about those rafts. For mammals colonizing large oceanic islands, it went something like this: Take the small number of natural rafts, about 10, that have been seen far out at sea in the past three hundred years or so. Multiply that by 100 to get an estimate of the actual number of such rafts—1,000—in that stretch of time. Assume that the Cenozoic Era is 60 million years long, and you get 200 million rafts during the Cenozoic. Of these 200 million, say that only 2 million have had living mammals on them. Of these 2 million, only 200,000 will have reached land, and of these 200,000, only 200 will have resulted in species establishing themselves in the new area. We only know of two dozen or so cases of mammals reaching large, oceanic islands on their own, so our calculation of 200 is more than enough to take care of all the known cases. And this is for mammals. It’s much easier for lizards or tortoises or sunflowers to get to such places.