The Beak of the Finch

In the Galápagos, there exist 13 species of finches—and some of them look so alike that they’re nearly impossible to tell apart. Yet in spite of their similar appearances, the birds are amazingly diverse. There are cactus finches that live and mate in the island’s cacti, drink their nectar, and pollinate them. There are vampire finches that feast on the blood of the blue-footed boobies that live on the islands. Each finch is highly specialized—and each species has a unique beak to go with their behaviors.

These finches have become more and more sophisticated in their uses of their tool-like beaks over time, thanks to the forces of evolution. The Grants’ research on the evolution of these finches—which takes place from season to season, year to year—is widely recognized as groundbreaking and completely unique in their field.

Darwin arrived in the Galápagos in September of 1835. He had joined the voyage of the ship the Beagle four years earlier, at just 22, serving as a companion to ship’s Captain FitzRoy. Though Darwin would become famous for analysis of the finches on the island, he mentioned them in his early diaries of his time in the Galápagos very infrequently and casually. He collected all kinds of specimens—fish, reptiles, insects, and nine kinds of finches, though he did not think the birds were particularly important. He didn’t realize at the time that they were all products of evolution and natural selection.

Having studied scripture at Cambridge, Darwin was still largely a Creationist—he believed that God had created all animals as the now were. Darwin drew on the research of the Swedish botanist Carolus Linnaeus, who had visited the Galápagos islands a century earlier in hopes of “glimps[ing] the plan of the Creator.”  Linnaeus was the first to divide life on Earth into kingdoms, classes, orders, genera, and species—a system many know now as the “tree of life,” branching ever outward. But Linnaeus believed that life forms on Earth hadn’t changed at all since their divine creator made them. Even observable variations between different kinds of plants didn’t convince him that life on Earth changed from generation to generation. 

Darwin’s time was full of scholars and thinkers who debated whether life was fixed or not—Charles Lyell, one such man, suggested a then-heretical view that while species were fixed, the Earth itself was ever-changing. Darwin had a sense that species could create variants of themselves, though he did not then imagine that the varieties of finches would become so important. But as he studied the specimens he had taken on the voyage back to England, he began to believe that the finches could “undermine the stability of Species”—they could plausibly show that species are changing over time.

In 1836, Darwin returned to London—and by early 1837, specialists at the Zoological Society there were already marveling at the 14 species of finches that had been created by the conditions in the Galápagos. The birds Darwin had brought back, the Society found, weren’t just varieties—they were a new, isolated species unique to the island. Though all of the specimens of birds and reptiles Darwin brought back bore a resemblance to their mainland counterparts in South America, they were all undeniably distinct from anything that had ever been found there. The society came to believe that these birds had diverged from their ancestors and “broken the species barrier.”

Darwin also brought back from his journey fossils of giant, extinct species of armadillo, llama, and capybara which proved that there was a “law of succession” linking living animals to their dead predecessors. Darwin had proof that species gradually changed over time—and he was “haunted” and thrilled by his own discovery. In the summer of 1837, he began writing about what he called the “Transmutation of Species”. Though he lamented having failed to label his specimens based on the islands where he’d found them, he began working toward a theory that selection was driving evolution.

Darwin knew that dog breeders could select for certain traits that would change the “character” of an animal. This process was already referred to as “selection”—so Darwin termed the phenomenon as it occurred in nature “natural selection.” In 1855—more than 20 years after his initial voyage—he began breeding pigeons, and soon wound up with 15 breeds that were technically the same species, though they’d been made distinct by nothing other than the process of selection. Darwin began to write about his findings. He knew that what he’d discovered in his own backyard implied that the power of nature could, over the course of millions of years, accomplish far greater things. 

Darwin’s realization about evolution wasn’t a single “eureka” moment—contrary to popular belief, even Darwin himself underestimated the mechanism of natural selection. And though Darwin himself never returned to the Galápagos, many naturalists who traveled there after him collected specimens of their own—and Darwin’s finches quickly became proof of evolution in action. Still, the Grants are the first people to actually watch the process of natural selection happen before their eyes.