The Beak of the Finch is an in-depth look at the research that was begun with Charles Darwin's brief visit to the Galapagos Islands through the late twentieth century with the Grants twenty years of visiting and researching on the islands. The book explains how Darwin's theories began, and how they were proven to be true, false, or just not totally correct. It also gives the reader an understanding of how evolution works over both long and short stretches of time.

The book is separated into three parts. Each part deals with a separate group of issues, but the parts flow together as one large story. There are no gaps or breaks in this chronology of two different time frames, Darwin's time and Grants' time.

Part one gives the reader a basic understanding of how Darwin's finches became famous and introduces the reader to the Grants and their research. It is miraculous that the finches received any attention, since Darwin did not believe they would be as useful as the mockingbirds he found on the islands. However, this turned out not to be the case, and the naturalists at the time honed in on the finches. Darwin, during his visit to the Galapagos, was certain the finches were not important. In fact, even though they made him famous, he did not include them in his book, "The Origin of Species." He did include later research of pigeons, but the finches are mysteriously absent.

Part two brings the Grants' research to the forefront of the book. It explains what they have been doing, what they are looking for, and some of the changes that have taken place over the twenty years of observing the finches. It gives the reader information on natural selection, sexual selection, and environmental changes that contribute to evolution. It also gives brief explanations of other researchers, who are also watching animals in nature and the laboratory and the findings that are very similar to those of the Grants. Just as the Grants, some of these researchers have been watching for twenty or more years. Others have just begun their observations, but were influenced by the Grants, such scientists as Dolph Schluster.

Part three leads the reader to the latter part of the twentieth century. Throughout the book, much of the Grants' time is fairy recent; however, this last section gives an idea of how the information from their research is being used. It includes the use of genetics in the research, and how geneticists are starting to create animals from the very basic ingredient, DNA. Part three leads the reader to have questions about the future of the planet, as well as the future of humanity. The projected future is not dark or warning of devastation, it is just how things the Grants are noticing in the finches gives insight for the future of the human race. This section also includes how the warmer climate of the world is starting to affect the finches. The Grants plan to keep their watch and see what happens.