The Beak of the Finch: Chapter 15 Summary & Analysis

On the floor below Princeton’s Natural History Museum is a drab basement corridor which leads to a subbasement—there, the Grants keep a Galápagos archive, containing hundreds of vials of the blood of Darwin’s finches. In his day, Darwin imagined a secret code that might be used to explain what determines the variations of species—today, of course, biologists and evolutionists recognize this secret code as a being’s genes.

Weiner watches as Peter Boag extracts DNA from frozen finch blood, bathes the DNA in an enzyme solution which fragments the DNA, and then transfers the fragments into a nylon bag. Boag is just one of many former finch watchers to “go molecular”—in other words, his research now focuses on DNA. Once Boag X-rays the DNA, he will be able to zoom in on small fragments that interest him—he is one of the first people to look at the DNA sequences of Darwin’s finches. 

A Galápagos finch has about 100,000 genes—about the same number as a human being—and those genes are spelled out in a total of roughly 1 billion letters. Only four letters make up the sequence: G for guanine, A for adenine, T for thymine, and C for cytosine. The finches’ genes are not fixed—they are shuffled and cut in each generation like a deck of cards, and each finch is completely unique. Mutations in the genetic sequence lead to variation: a mutation might cause cancer, or it might confer a small benefit on the finch, allowing it to survive and pass that favored mutation on again and again. Boag looks for slight differences in the sequences of letters that make up the birds’ DNA.

Evolutionists can learn more about “the lost history of life” from studying DNA. They can discover which animals are related, and how. Just as historians can now backdate Darwin’s manuscripts based on spelling errors he made at certain points in his life, biologists can sort out how Darwin’s finches have changed and when the most major changes took place. The finches that look most different—for instance, warbler finches—are those that have been evolving for the longest. Mutations spell out the answers to when certain species began to diverge—but because genes are like manuscripts that are being written and revised constantly, there are still many answers that evade Boag and his team.

In times of stress, species like bacteria have been observed to start evolving wildly—it is a kind of SOS response, increasing the chance that at least a few cells will gain the variations necessary to survive the changing environment. This same response has been seen in plants—and many evolutionists, including the Grants, believe that the same thing has happened (and is now happening) to Darwin’s finches. A major event seems to be taking place.