The Beak of the Finch

by

Jonathan Weiner

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The Beak of the Finch: Chapter 12 Summary & Analysis

Summary
Analysis
Nowhere in his writings does Darwin contemplate the moment of divergence itself—the moment when one line of a species splits into two. Weiner calls this “the cosmic parting.” But today, as more and more naturalists study evolution in action, they keep an eye out for these “cosmic” splits. Researchers have been able to observe these splits in species like fruit flies and conclude the definitive fact that “each species first existed as a variety,” as Darwin wrote so long ago. By observing many generations of fruit flies in lab conditions, evolutionists have watched “incipient species” arise—these new species are unable to produce fertile offspring with specimens that were, just a few generations ago, their kin. 
Even though Darwin wasn’t able to witness many parts of the evolutionary process in the wild during his lifetime, researchers today are far better equipped to capture these delicate moments in action. Because the process of evolution takes place gradually, it can be difficult to pinpoint the “cosmic” moment at which a species has diverged enough to constitute a new species entirely—but researchers have worked tirelessly to isolate and define that moment nonetheless.
Themes
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The question of how new adaptations arise from gradual beginnings is one of the central questions of Darwinism. Darwin himself used the example of the evolution of the human eye to suggest that all the sophistications that exist within it grew gradually, in stages, through natural selection for advantageous traits, also called adaptive traits. Adaptive traits are more likely to be preserved—even though the process of creation is, essentially, “blind”—with the result that the advantageous traits build on themselves over time.
While evolution in an isolated place like the Galápagos can begin to take place quickly, evolution is very often a slow and painstaking process in which new, advantageous traits emerge gradually. This illustrates what an intense process evolution is: natural selection, sexual selection, and environmental pressures are all factors in the production and preservation of new traits that help a species to survive and thrive.
Themes
Natural Selection and Evolution as Ongoing Processes  Theme Icon
The Interconnectedness of Species and Ecosystems Theme Icon
Hybridization and Specialization Theme Icon
In 1991, two researchers at the University of British Columbia studied a genus of finches native to North America, Europe, and Asia called crossbills—their beaks, as their name suggests, are crossed. Their twisted bills are adaptive, because these finches eat pinecones and need twisted beaks that allow them to pry the cones open. The researchers clipped the bills of the finches—a harmless process akin to clipping fingernails—so that they were uncrossed. The birds struggled with their food sources, but as their bills grew back, they did better and better.
This experiment revealed something monumental about the evolutionary process. Any crossing of the bill at all helped the finches a little—so the crossed bill could have arisen gradually rather than all at once. This illustrates that the process of evolution is at work from generation to generation, weeding out individuals whose traits aren’t different enough to survive while prospering those whose physical traits allow them to better interact with their environment. 
Themes
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The Interconnectedness of Species and Ecosystems Theme Icon
Hybridization and Specialization Theme Icon
Dolph Schluter has begun a new study near Mandarte Island, in the Strait of Georgia—a body of water which is full of three-spined sticklebacks, small salt-water fish who sometimes migrate into fresh water. For 12,500 years, the fish have been evolving in freshwater lakes—just like the finches on Daphne Major. Most lakes in the region hold just one species, but a few lakes hold two. One species (benthics) feeds along the bottom, and one (limnetics) above it. By carefully measuring the fish, Schluter and his team have mapped how selection is acting on the fish.
This passage sets up Schluter’s experiment. By focusing on a genus of animal containing two specialized species, Schluter was able to predict how they would behave—and from there, he could watch how environmental differences would impact the fish.
Themes
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The Interconnectedness of Species and Ecosystems Theme Icon
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In every lake that contains two species of sticklebacks, the team has found, the two species are divergent in the same way: one always feeds on the bottom, and one always feeds higher up. Benthics are bigger and fatter, while limnetics are small and thinner. The pattern has repeated itself in five different lakes. Even in one lake where all of the fish are technically the same species, the smallest difference in their sizes dictates where they’ll feed. Speciation, in other words, is in progress. The populations are ready to respond, at all times, should selection pressure arise. And what’s more: these species have altered the course of one another’s evolution, filling niches that the other cannot.
This passage shows that the fishes’ instincts and appearance drive their behavior. Bigger fish fill one niche, while smaller fish fill another. Just like the finches, the similar fishes have found out how to stay out of one another’s way—and thus ensure their own survival. This experiment is also important because it shows that any given species is influenced heavily by its ecosystem, and that includes any neighboring species.
Themes
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The Interconnectedness of Species and Ecosystems Theme Icon
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Quotes
Schluter predicts that the species will continue evolving toward their respective peaks. Because the species are rare and protected, Schluter can’t do the kinds of experiments he’d like to—but the ones he has done have made it clear that competition affects populations today, and that natural selection pressurized by competition can be observed. Schluter plans to create a hybrid of benthics and limnetics—then place those hybrids in two false ponds, one containing only benthics and one containing only limnetics, and see how the hybrids change in each pond to fill the niche exposed by their counterparts.
The next phase of Schluter’s experiment promises to reveal how long it takes for a hybrid species to specialize. Schluter’s work is significant because it carefully explores the process of specialization—even among hybrid populations that might not necessarily be suited for one specialty over another.
Themes
Natural Selection and Evolution as Ongoing Processes  Theme Icon
The Interconnectedness of Species and Ecosystems Theme Icon
Hybridization and Specialization Theme Icon