The Beak of the Finch: Chapter 7 Summary & Analysis

Lisle Gibbs and his field assistant rushed to Daphne Major to find nests all over the island crowded with baby finches—the wet season had come on fast and furious, earlier than any year on record since the founding of the Darwin Research Station in 1960. The rains over the next few weeks were torrential, leading to landslides and flash floods. The source of the storms was El Niño—the Child—a weather phenomenon that generally appears every three to six years. During El Niño, a patch of warm water appears in the eastern Pacific and spreads, warming the rest of the ocean. The warmer water creates uncommon winds and weather events all over the world.

The El Niño that Lisle Gibbs and his assistant experienced was the strongest recorded in the 20th century. The desert island of Daphne Major was transformed into a veritable jungle; trees flowered, creating a “bumper crop” of seeds for the finches to enjoy. In contrast, neither the cactus nor the Tribulus plant could survive the wet weather. The birds “bred like hell”—even the juveniles—and, by June, there were over 2,000 finches on Daphne Major. On Genovesa island, though, the finches often abandoned their nests (or lost them to snapping branches). Juvenile mockingbird populations on the island, abandoned by their elders after a pox took most of them out, began roaming the island and terrorizing the finches by eating their eggs and attacking their young.

The rains stopped eventually, and, by autumn, Daphne Major was dry once more. But the finch population remained huge, and the seeds left by the floods were still plentiful enough to support that population—for a while. But the following year, only 4 millimeters of rain fell, and the resources on the island could no longer support such a large group of finches. Their populations began to crash.

Back in the U.S., Lisle Gibbs looked at his research. It was September of 1985. What he found was astonishing: natural selection had swung back around. Now, big birds with big beaks were dying—and small birds with small beaks were flourishing. As it turned out, the traits that had been advantageous in a drought were liabilities in a wet season. More tiny seeds were buried in the island’s soil—so smaller birds with narrower beaks could find them and get at them more easily than their larger counterparts, whose big beaks got in the way of the delicate work of seed-selecting. And as the seed supply ran low, these already struggling big-beaked birds found it even harder to compete.

The selection pressures of nature aren’t static—instead they often oscillate, and sometimes, as in the case of the late 1970s and early 1980s in the Galápagos, they do so “violently”.

A finch watcher (and student of the Grants) named Jamie Smith began watching sparrows on Mandarte, an island off the coast of British Columbia, and believed his research showed no selection amongst the population he was studying. But another Galápagos veteran named Dolph Schluter reviewed Smith’s research. After breaking down the sparrows’ lives on a closer level, he found that selection had actually been working on them “ruthlessly” from year to year—in other words, a lot of small changes were happening in the species. But on a longer timeline, these forces were invisible. The variations in the Mandarte sparrows were much harder to observe than those in the Galápagos finches, because “stabilizing selection”—a force that seeks to make all of the sparrows the same—is working on them. 

Darwin believed that evolution was an extraordinarily slow process, because the fossil records he could observe were static and frozen for long periods of time. He had trouble seeing evolution at work on a large scale. But in reality, the forces of natural selection and evolution are happening each and every day—one just has to know where to look to see these minute forces in action.

In 1949, an evolutionist by the name of J.B.S. Haldane suggested the rate of evolution be described in terms of a universal unit—he decided to call this unit the “darwin” and to define it as a rate of change of 1 percent per million years. Fossil records he looked at showed a rate of change of a single darwin, and so he concluded that the rate of evolution by natural selection was too slow to observe. But in the case of the drought and flood in the Galápagos in the late 1970s and early 1980s, the rate of change was 25,000 darwins during the drought and 6,000 during the flood. When seen in action, the evolutionary processes of the living world look much different than the ones recorded in stone.

Ironically, if a species changes one way and then another in rapid succession, the official record would show little or no change at all. But things like the beak of the finch are in such fast evolutionary motion that all it takes is a careful observer to discover astonishing rates of change. “Life,” Weiner writes, is in “perpetual readiness to take off in any of a thousand directions.”