The Next Species: The Future of Evolution in the Aftermath of Man (6 page)

M
OST SCIENTISTS AGREE
that the slow, lateral movement of the continents, their joining and separating on the surface of the planet, has strongly influenced the broad diversity of plants and animals that exist on earth today. During the Permian period all the continents joined together in one enormous landmass, a supercontinent, but after that extinction event, the supercontinent Pangaea began to split apart like a broken dinner plate with its pieces scattered across the oceans. This separation of the landmasses led to a corresponding separation of species of plants and animals. Newly separated species no longer exchanged genes with one another and over time isolated populations evolved away from each other and became separate species.

The splendor of this evolutionary tale was on display when Darwin and the crew of HMS
Beagle
rowed up to the island of San Cristóbal, a black mound of volcanic rock in the middle of the Pacific Ocean, during their celebrated visit to the Galápagos Islands that began on September 17, 1835. At a distance the island looked desolate, but upon landing Darwin found it covered with plants that bore leaves, flowers, and seed-bearing fruits. He had been on a four-year expedition to South America and was now heading across the
Pacific on the long way back home to England. The crew of the boat hoped to catch a tortoise for some meat to make a tasty soup, but there were no tortoises on San Cristóbal.

He did find numerous birds, which were unfazed by human presence as they looked for seeds in the bushes; they’d had no experience with humans. One of the crew even caught a bird with his hat. Darwin picked up an iguana and threw the animal into the water over and over, but each time it swam straight back to him. He yanked on the tail of another that was digging a burrow, and it turned and looked at him as if to say, “What made you pull my tail?”

The
Beagle
docked in the Galápagos Islands for five weeks, during which Darwin accumulated plants and animals, focusing on the many birds. He thought he was collecting blackbirds, wrens, and warblers, but when he got them back to London, an ornithologist told him that though the birds looked different they were all finches. Plus Darwin had stored birds in bags by type and hadn’t separated much of his collection by island, which he later found was important. He’d assumed they were the same species he’d seen on mainland South America.

He did notice that the mockingbirds he’d taken on the second island seemed different from the ones on the first, so he started labeling them. When the vice governor of the islands told Darwin that he could distinguish the tortoises on one island from the tortoises on another, Darwin ignored him at first. Darwin did not imagine that these animals could have originated from a few animals blown across the Pacific and that they had diversified into different species on different islands within clear sight of one another. Darwin held, as did many scientists at that time, that these animals were all the same. Differences in color and form were indicative of different varieties, not separate species.

The definition of a species, according to Ernst Mayr, a German-born American biologist, is “groups of interbreeding natural populations reproductively isolated from other such groups.” This definition didn’t seem to fit the samples of wildlife Darwin had collected. These islands were in sight of one another. Surely separate species could not form on places so close. But they had indeed.

When Darwin returned to England, he gave all his bird skins and other trophies to the Zoological Society of London, and the ornithologist John Gould took a fresh look at them. At the next meeting of the society, Gould professed his excitement over Darwin’s findings of a new group of “ground finches.” The
Daily Herald
the next day reported on the meeting, noting the fourteen species of ground finches, “of which eleven were new forms none being previously known in this country.” This finding heralded an important moment in the evolution of Darwin’s
On the Origin of Species
, though it would be twenty-three more years before the book was published.

The fossils Darwin collected in South America were unique as well. Among them were a giant llama, a giant armadillo, and a rodent as big as a rhinoceros. Wherever one followed the trail of life, across the land or back through time, “species gradually become modified,” wrote Darwin. He was beginning to realize how new species might evolve, but he had no idea at the time what a large role continental drift had played in the process.

On the voyage of HMS
Beagle
, Darwin brought
Principles of Geology
by Charles Lyell along for reading. Though his Cambridge professors had warned him to take the book with a grain of salt, he enthusiastically accepted Lyell’s view of the earth changing restlessly beneath man. Darwin had witnessed this change in his journeys through South America. Still, both thought the movement of the continents was upward and downward, and that nothing moved laterally.

Darwin had no idea yet how important both the vertical and horizontal movement of the continents on the surface of the earth was to evolution.

The mid-1800s were a time of upheaval in biological as well as geological thought. The British Empire was in full bloom and the most famous of the early geological surveys date from this era. The Industrial
Revolution had arrived earlier with an insatiable hunger for iron, coal, oil, and other deposits, and thus geologists became the celebrities of the day. They earned their keep by uncovering industrial resources, and in accordance with the spirit of discovery that ruled then, these geologists weren’t afraid to address more theoretical issues, like how these resources came to be.

Brothers
William and Henry Blanford, members of the Royal School of Mines in London, were offered posts with India’s newly hatched geological survey and were sent to investigate the Talcher Coalfield in the state of Orissa in that country. The Blanfords started digging and in 1856 found that below this enormous bed of coal was yet another formation of large boulders embedded in fine mudstone, and there was telltale evidence of a glacier. The boulders all had the markings of glacial scour—the abrasions, scratches, and polish of glacial ice against rock. Furthermore, some of the boulders had been moved large distances, another telltale sign of glacial action.

This showed that before Talcher had become one of India’s largest coal deposits, formed by steaming tropical swamps, it had been part of an enormous ice field. The Blanfords returned to Calcutta and reported to their boss that ice sheets had once covered India. But this raised important questions in the geological community. How could glaciers form in the tropics? Had India once been much closer to the poles? Did continents move?

Further evidence for the shift of landmasses was uncovered in 1912 when
Britain’s Captain Robert Scott led a harrowing expedition to the South Pole, having to cope with blizzards and temperatures as low as minus 23 degrees. Though he and his men made it, they did so thirty-three days after a Norwegian team. Captain Roald Amundsen, its leader, left a Norwegian black marker flag and a note to the British at the pole. Losing the race for his country was enormously disconcerting for Scott, who wrote in his diary: “The POLE. Yes, but under very different circumstances from those expected. Great God! This is an awful place and terrible enough for us to have labored to it without the reward of priority.” Scott and most of his men froze to death trying
to get back, though they’d carried most of their finds almost the distance.

Scott’s second in command, Edward Evans, survived, but upon returning to New Zealand wrote a letter criticizing their leader for not jettisoning all records and specimens of weight that the party had collected on their treacherous adventure. Scott and the team members Edward Wilson and Henry Bowers had died in a tent that was but 12.7 miles (20 kilometers) south of One Ton Depot, a spot on the Ross Ice Shelf where the party had cached food and supplies. Scott’s body was found beside thirty-five pounds of coal and fossil rocks that the captain apparently considered more sacred than his own life. The samples included the first find this far south of
Glossopteris
, a seed fern that had become extinct over 200 million years ago. For such a tree to survive, a much warmer climate than the icy world Scott had found at the South Pole would have had to exist, scientists speculated. Or maybe the land that the South Pole stood upon had once been in the tropics?

Alfred Wegener, a German geophysicist, who first described the lateral movement of the earth’s great landmasses in his 1915 book
The Origin of Continents and Oceans
, gathered evidence for this argument. Wegener noted that the continents of Africa and South America fit together quite nicely, and he found reports that fossils on the adjacent coastlines of both continents were similar. Scientists had previously suggested that land bridges once joined them, but Wegener countered this belief, saying that they had moved. He noted that India, Antarctica, and Australia looked like they could fit together, and proposed that they had all once been joined in a supercontinent that he called Pangaea. His book was the first place that name appeared. Wegener proposed that the world of today was but the dispersing remnants of this supercontinent, which 250 million years ago began to break apart.

Continental drift, or the slightly more evolved concept of plate tectonics, has been for scientists the driving engine behind evolution and the creation of new species for over a hundred years. In the days of the great Pangaea, all major landmasses had gathered together, and
this merging of lands coalesced life—the outcome being fewer species. But as Pangaea began to separate, the isolation that followed proved the best breeder of species, creating a greater number of plants and animals.

There are, however, other ways to make new species. Alfred Russel Wallace, often credited with cofounding the theory of evolution, traveled through the Amazon and Southeast Asia in the mid-1800s. He studied hundreds of animals and tried to determine why they were found where they were. He thought it was significant that rivers and mountain ranges frequently marked the boundaries of species ranges. Many scientists believed that climate determined a species’ range, but Wallace found similar climate regions with very different species and declared that geography had a lot more to do with it.

This theory of island biogeography, as promoted by Wallace and others, began as a way of explaining the species richness of actual ocean or lake islands, but grew to incorporate the species richness of landlocked islands as well. Scientists modified their definition of islands in the late twentieth century to include other isolated habitats such as mountains surrounded by deserts, lakes surrounded by dry land, and natural habitats surrounded by landscapes altered by man. Today, scientists have modified this concept further, using it to explain any ecosystem surrounded by divergent ecosystems. It could be an island surrounded by water, or a spring surrounded by desert, a mountain peak surrounded by lowlands, or grassland surrounded by human housing.

It is not a simple concept. What is
considered an island for one organism may not be an island for another: some organisms located on mountaintops may also be found in valleys, being adaptable to both elevations. But others may be ecologically adapted only to the peaks and thus view the valleys as chasms that cannot be crossed. It may depend
on whether the animal is a generalist, suitable to a wide range of environments, or a specialist, adapted to a much more specific niche. Isolated environments created in a mountain range can increase the variety of species in the range overall.

A
typical example of a landlocked island is the mountainous region of Vilcabamba, the range in the Andes that I visited with Conservation International biologists. Deep river valleys surround the mountaintops, isolating them just like an ocean. The cloud forests here house many unique species, including some that have yet to be identified by scientists. Vilcabamba is a monument to natural diversity, as it showcases the broad range of possibilities to life.

On the day after Peruvian army helicopters had deposited our team into the dripping-wet cloud forests of Vilcabamba, I got up before dawn to survey the area’s birds with Tom Schulenberg, an ornithologist with the Cornell Lab of Ornithology. We skirted the bog in the middle of the forest near our campsite looking for the feathered creatures, careful to avoid wet sinkholes in the moss that could swallow one’s leg up to the thigh. Schulenberg aimed binoculars as well as microphones at the edge of the forest, claiming he could hear four times as many birds as he could see. Though the elevation here was too high for parrots and toucans, the ornithologist’s Peruvian assistant, Lawrence López, captured a plush-capped finch, an Azara’s spinetail, and a yellow-scarfed tanager that he pulled from his jacket pocket and proclaimed, “Look at that beauty,” before he released it.

In the evening, I followed Mónica Romo, a biologist with the office of Conservation International in Lima, Peru, who set nets by the forest edge to capture bats that she estimates spread almost 50 percent of the seeds in the forest through their feces. The next day I followed Romo down trails freshly cut with a machete to lay mammal traps. Romo was knowledgeable about all these animals, but also bore
a self-professed sweet tooth, and was envious when the camp’s peanut butter was added to the bait used to capture these small creatures. “I hope they appreciate it,” she said. Mindful of the presence of fer-de-lance, one of South America’s most potent and aggressive vipers, I stowed my traps in the open, while Romo hid hers in every dark corner. They collected forty species of mammals, including a very large rodent that had never been described before.

A few days later, I accompanied Brad Boyle, a Canadian botanist who specializes in tropical plants. With his Peruvian counterparts, he laid a 165-foot (50-meter) line in the forest and started taking plant specimens on either side. He directed my attention to the orchids, bromeliads, mosses, and ferns perched on the limbs of the trees above, and declared that there were more species in that cluster of treetops than in most northern forests.