Carl Zimmer - Evolution - The Triumph of an Idea

But when Charles Darwin traveled to Edinburgh, a city where radical ideas thrived, he discovered that his grandfather had many admirers. One of them was Robert Grant, the zoologist who became Charles’s mentor. Grant studied sponges and sea pens not out of idle interest, but because he thought they lay at the root of the animal kingdom. From forms like them, all other animals might have descended. When Grant and Darwin went hunting for specimens in tide pools along the shore, Grant would explain to young Charles his admiration for Erasmus Darwin and his ideas of transmutation, a process by which one species changes into another. And Grant explained to Erasmus’s grandson that there were French naturalists who had also dared to contemplate the possibility that life was not fixed—that it evolved.

Grant described a colleague of Cuvier’s at the National Museum of Paris named Jean-Baptiste Pierre Antoine de Monet, chevalier de Lamarck. In 1800, Lamarck shocked Cuvier and the rest of Europe by declaring that the fixity of species was an illusion. Species had not all been created in their current form at the dawn of time, Lamarck proposed. Throughout the course of Earth’s history, new species formed through spontaneous generation. Each came into existence equipped with a “nervous fluid” that gradually transformed it, over the course of generations, into new forms. As species evolved, they achieved higher and higher levels of complexity. The continual emergence of species and their ongoing transformation created the Great Chain of Being: lower members of the chain had simply started their upward journey later than higher members.

Life could change in another way, Lamarck claimed: a species could adapt to its local environment. Giraffes, for example, live in places where the leaves are far from the ground. The ancestors of today’s giraffes might have been short-necked animals that tried to eat the leaves by stretching their neck upward. The more an individual giraffe stretched, the more nervous fluid flowed into its neck. Its neck grew longer as a result, and when it produced baby giraffes, it passed on its longer neck to them. Lamarck suggested that humans might have descended from apes that left the trees, stood upright, and walked out onto the plains. The very effort of trying to walk on two legs would have gradually changed their bodies to our own posture.

Most other naturalists in France and abroad were appalled by Lamarck’s ideas. Cuvier led the attack, challenging Lamarck for evidence. The nervous fluid that made evolution possible was a complete conjecture, and the fossil record didn’t back him up. If Lamarck were right, the oldest fossils should on the whole be less complex than species are today. After all, they had had less time to rise up the scale of organization. Yet in the oldest rocks that were known in 1800, there were fossils of animals as complex as anything alive today. Cuvier found another opportunity to attack Lamarck when Napoleon’s armies invaded Egypt and discovered mummified animals buried in the tombs of the pharaohs. Cuvier argued that the skeleton of the sacred ibis, which was thousands of years old, was no different from the sacred ibis alive in Egypt today.

Most naturalists in Great Britain, steeped in Paley’s natural theology, were even more repulsed than Cuvier. Lamarck was reducing mankind and the rest of nature to the product of some unguided, earthly force. Only a few heretics such as Grant admired Lamarck’s ideas, and for their heresy they were shut out of Britain’s scientific inner circle.

Grant’s praise of Lamarck took the young Darwin by surprise. “He one day, when we were walking together, burst forth in high admiration of Lamarck and his views on evolution,” Darwin later wrote in his autobiography. “I listened in silent astonishment, and as far as I can judge, without any effect on my mind.”

By the time Darwin boarded the Beagle four years later, evolution had sunk away from his thoughts altogether. Only after he had returned from his voyage would it rise back again, and in a radically different form.

The voyage started badly. Darwin arrived in Plymouth in October 1831, but it wasn’t until December 7, after weeks of repairs and delays and false starts, that the Beagle set sail. And as soon as Darwin left shore, he became horribly seasick, spewing his meals over the rails. Although Darwin would sail for five years on the Beagle, he never managed to get his sea legs.

Darwin found being FitzRoy’s companion a tricky job. The captain’s temper was sharp and unpredictable, and his navy discipline was a shock to Darwin. On Christmas some of the Beagle’s crew got drunk, and FitzRoy had them flogged the following day. Each morning after Darwin emerged from breakfast with FitzRoy, the junior officers would ask, “Has much coffee been spilled this morning?” as a coded way to check on the captain’s mood. But Darwin also respected FitzRoy’s powerful drive, his dedication to science, and his devotion to Christianity. Every Sunday Darwin attended the captain’s sermons.

Darwin yearned for landfall, but it did not come for weeks. At Madeira, the currents were so bad that FitzRoy decided not to anchor there, and at the next port—the Canary Islands—a cholera epidemic was raging. Rather than waste time in a quarantine before going on shore, FitzRoy simply sailed on.

Finally, the Beagle stopped for the first time in the Cape Verde Islands. At Saint Jago, Darwin bounded off the ship. He darted about beneath the coconut trees, looking at the rocks, the plants, the animals. He found an octopus that could change colors, from purple to French gray. When he put it in a jar in the hold of the ship, it glowed in the dark.

But it was the geology of the island that Darwin most wanted to see. On the journey from England, Darwin had been engrossed by a new book called Principles of Geology, written by an English lawyer named Charles Lyell. It would change the way Darwin viewed the planet, and ultimately lead him to his theory of evolution. Lyell attacked the catastrophe-centered geology that was popular at the time, reviving Hutton’s 50-year-old theory of a uniformly changing Earth.

Principles of Geology wasn’t simply a rehash of Hutton’s ideas. Lyell offered a much richer, scientifically detailed vision of how the changes humans witness could have gradually shaped the planet. He offered evidence of volcanic eruptions building islands, of earthquakes having lifted land; he then showed how erosion could grind these exposed features down again. Geological change was happening slowly, imperceptibly, Lyell argued, even over the course of human history. The frontispiece of Principles shows the ancient Roman temple of Serapis, with dark bands marking the tops of its pillars, caused by mollusks that at some point had drilled into them. Within the lifetime of the temple it had been completely submerged and then raised from the ocean again. Unlike Hutton, Lyell didn’t see Earth going through a grand, global cycle of creation and destruction. The planet changed locally, eroding here, erupting there, in a state of perpetual, directionless flux for an unimaginable span of time.

Darwin was fascinated by Principles of Geology. He realized that it offered not only a compelling vision of Earth’s history but a method for testing it against the real world. When he landed at Saint Jago he had an opportunity to do just that. He scrambled over the volcanic rock of the island and found clues that the lava had originally poured out underwater, baking coral and shells as it spread. Subterranean forces must have later lifted the rock up to the sea’s surface, but they must have then lowered it back down and lifted it up yet again. Some of the rising and falling must have happened only recently, Darwin realized, for in a band of rock in the cliffs he could find fossils of shells that matched those of creatures still alive around the island. Earth was changing in 1832, as it had for eons.