The highly variable beaks belonging to the different species of Galápagos finches—animals that are often called “Darwin’s finches”—symbolize the power of natural selection and evolution. The book suggests that the enormously different beaks of the finches found throughout the Galápagos, and specifically on the volcanic island of Daphne Major, are proof of evolution. But, as the book explains, people throughout history—from Darwin’s era in the mid-1800s all the way up to the modern day—resist subscribing to the belief that life is constantly evolving, sometimes claiming instead that all of life was created in an instant by God (this belief is called Creationism). The beaks of Darwin’s finches, though, symbolize the powerful and remarkable ways that evolution diversifies life on Earth not just over thousands or millions of years, but sometimes from hour to hour or day to day. Everything on Earth, the book posits, from bacteria to plants to animals, is always changing due to a steady stream of unseen selective pressures that force life to adapt favorable traits in order to survive. The ever-changing beak of the finch is one of the most easily observable pieces of evidence for evolution that any species on Earth possesses. Thus, the author Jonathan Weiner uses the beak of the finch to symbolize how powerful and omnipresent evolution really is.
The Beak of the Finch Quotes in The Beak of the Finch
The whole family tree of Darwin’s finches is marked by this kind of eccentric specialization, and each species has a beak to go with it. Robert Bowman, an evolutionist who studied the finches before the Grants, once drew a chart comparing the birds' beaks to different kinds of pliers. Cactus finches carry a heavy-duty lineman’s pliers. Other species carry analogues of the high-leverage diagonal pliers, the long chain-nose pliers, the parrot-head gripping pliers, the curved needle-nose pliers, and the straight needle-nose pliers.
Only varieties. If so, they would fit comfortably within the orthodox view of life. But what if they were something more than varieties? […] What if there were no limits to their divergence? What if they had diverged first into varieties, and then gone right on diverging into species. new species, each marooned on its own island?
“—If there is the slightest foundation for these remarks,” Darwin wrote, “the zoology of Archipelagoes—will be well worth examining; for such facts undermine the stability of Species.” Then, in a scribble that foreshadowed two decades of agonized caution, Darwin inserted a word: “would undermine the stability of Species.”
According to [Darwin’s] theory, even the slightest idiosyncrasies in the shape of an individual beak can sometimes make a difference in what that particular bird can eat. In this way the variation will matter to the bird its whole life—most of which, when it is not asleep, it spends eating. The shape of its particular beak will either help it live a little longer or cut its life a little shorter, so that, in Darwin's words, "the smallest grain in the balance, in the long run, must tell on which death shall fall, and which shall survive."
Now it became of great significance that variations of body and beak are passed on from one generation to the next with fidelity. As a result, the males' unequal luck in love helped to perpetuate the effects of the drought. The male and female fortis that survived in 1978 were already significantly bigger birds than the average fortis had been before the drought. Of this group the males that became fathers were bigger than the rest. And the young birds that hatched and grew up that year turned out to be big too, and their beaks were deep. The average fortis beak of the new generation was 4 or 5 percent deeper than the beak of their ancestors before the drought.
So the birds were not simply magnified by the drought: they were reformed and revised. They were changed by their dead. Their beaks were carved by their losses.
In most places on this planet, the sight of a dead bird is so rare that it shocks us, even scares us. […]
But on the desert island of Daphne Major, dead birds are commonplace. They are everywhere. […] Each generation lies where it falls, and the next generation builds on the ruins of the one before.
Natural selection had swung around against the birds from the other side. Big birds with big beaks were dying. Small birds with small beaks were flourishing. Selection had flipped.
Both big males and big females were dying, [Gibbs] noticed, but many more males than females—again, the reverse of the drought. Everything the drought had preferred in size large—weight, wingspan, tarsus length, bill length, bill depth, and bill width—the aftermath of the flood favored in size small.
Half a millimeter can decide who lives and who dies. Since these slight variations are passed down from one generation to the next, the brood of a small beak and a medium beak would be likely to have intermediate beaks, equipment that would sometimes differ from their parents' not by one or two tenths of a millimeter but by whole millimeters, maybe by many millimeters. […] Daphne Major is not a forgiving place. A line of misfits should not last.
[…]
That is why the Grants are so puzzled now.
The conclusion is inescapable: the feature that makes the finches most interesting to us is also the feature that makes them most interesting to each other. When they are courting, head to head, making decisions that are fateful for the evolution of their lines, Darwin’s finches are studying the same thing as the finch watchers. They are looking at each other's beaks.
Thus the Grants suspect that the finches here are perpetually being forced slightly apart and drifting back together again. A drought favors groups of one beak length or another. It splits the population and forces it onto two slightly separate adaptive peaks. But because the two peaks are so close together, and there is no room for them to widen farther apart, random mating brings the birds back together again.
These two forces of fission and fusion fight forever among the birds. The force of fission works toward the creation of a whole new line, a lineage that could shoot off into a new species. The force of fusion brings them back together.
These two oscillations are driven by the same events. They are both governed by the same changes in the adaptive landscape. In an adaptive landscape that is wrinkling and rolling as fast as Daphne, a landscape in which the peaks are in geological upheaval, it can pay to be born different, to carry a beak 3, 4, or 5 millimeters away from the tried and true. Since the super-Niño, some of the old peaks have turned into valleys, and some of the old valleys are peaks. Now a hybrid has a chance of coming down on the summit of a new peak. It can luck onto a piece of the new shifting ground.
The Beak of the Finch Symbol Timeline in The Beak of the Finch
