The Beak of the Finch

by Jonathan Weiner
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Last Updated on June 19, 2019, by eNotes Editorial. Word Count: 183

The Beak of the Finch by Jonathan Weiner is about two scientists who explore Charles Darwin's theory of evolution. The author reveals that Peter and Rosemary Grant, the scientists, believed Darwin did not fully understand the importance and relevance of his theory. The two scientists observed how natural selection applied to finches. They concluded that natural selection is continuous and always taking place.

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Weiner provides an in-depth description of the processes that the two scientists went through to make their research successful. Furthermore, he interviews several biologists who focus on other animals. They collect information that Darwin did not, and they explain how the Grants motivated them to study more about evolutionary changes.

The author reveals the mystery and beauty in evolution and analyzes Judeo-Christian beliefs concerning evolution without bringing up the concept of God. He reveals interesting views about the pattern of evolution in different environments. The author also discusses the formation of species and implies that it does not occur because of geographical isolation. Furthermore, Weiner explains how hybrids are produced and the role they play in the formation of species.


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Last Updated on May 5, 2015, by eNotes Editorial. Word Count: 1998


Volcanic islands represent ideal laboratories for the study of ecology and living forms, for they permit flora and fauna to develop in almost complete isolation. From their origin as sterile masses of lava, over millennia they gradually develop topsoil; then seeds—borne by sea birds, by floating debris, or by humans on brief stops—begin to grow and develop. Once plant communities have been established, they form the basis for animal populations of marine mammals, pelagic birds, or insects and passerine birds blown off migratory courses by storms. A few small land vertebrates, depending on ocean currents, may arrive on floating rafts of vegetation. Once animal life has secured a foothold, it must cope with a climate, terrain, and ecology very different from those of its original habitat. In response, it adapts to the new conditions, over time developing into new and hitherto unknown species. Among the numerous volcanic islands of the world, the most famous are the Galápagos chain off the coast of Ecuador, which Charles Darwin visited in 1835 as a naturalist aboard HMS Beagle.

During his stops among the islands, Darwin collected specimens of flora and fauna for further study in England, as he had done in other locations on the voyage. The collected species included several finches of a kind he had never seen; all were similar in color but variable in size and behavior. Most striking to Darwin were the varying sizes of their beaks, suggesting different feeding patterns, though at first he saw little scientific significance in that fact. After returning to England, he posted their skins to the ornithologist John Gould in London and was surprised by his verdict that the finches belonged to previously unknown species. In time, the fourteen species of finches inhabiting the islands became the most studied group of birds in the world. Once it had been determined that they were all descended from a single species, numerous scientists have attempted to explain how this differentiation occurred. Since Darwin’s time, one of the native Galápagos species, the largest and the weakest flyer among them, has become extinct, but thirteen species remain on the islands.

Jonathan Weiner’s book is primarily an account of one such study of Galápagos finches. Despite its extensive scientific bibliography, it is not a scientific report but rather a narrative of the project of Peter and Rosemary Grant, who have led an ongoing study from Princeton University for the past twenty-one years. They have centered their study upon the ground-feeding finches indigenous to one small uninhabited island, Daphne Major, near the center of the Galápagos chain. While the ground feeders comprise six species, Daphne Major has only three or four species in any numbers. Lacking a freshwater source, the island offers researchers only primitive, stark living conditions. Its forbidding nature, however, ensures that life there has developed without human interference, a fact no longer true of the larger neighboring islands.

Hardly more hospitable to birds than to humankind, Daphne Major’s climate consists of a wet and a dry season. If seasonal rains are adequate, the finch population reaches two thousand or somewhat over that, but during the subsequent dry season, the population declines drastically to as few as three hundred during a severe drought. Because of the limited population of finches on Daphne Major and their relative tameness, the Grants have been able to capture and band every bird. Since nests are easily located amid the rather sparse vegetation, unfledged chicks are banded while they are still in the nest. The bands are designed so that individuals within the population can be identified by sight. Rarely, outside a confined area, could a researcher find a limited and easily accessible avian population for a study of this kind.

Unlike earlier researchers, the Grants have taken care to do as little harm to the finches as possible during their long period of study. Mist nets have long since replaced shooting as a means of capturing birds for study (during the early twentieth century thousands of Galápagos finches were shot for scientific study). The procedures used today enable researchers to compile adequate data while interfering little with the daily life of the birds.

Data obtained by the Grants include measurements of beak size, body weight, and wing span as well as records on reproduction and longevity of each bird. In addition, blood samples from individual birds are preserved for further study of alterations in DNA. As is usual in such studies, diets are determined through examination of the intestinal contents of dead birds. Over the twenty-one-year period, the Grants have accumulated data on eighteen thousand individuals. The sheer volume of data is manageable only through computers, and much of their time back at Princeton is spent analyzing the amassed data.

Their project is one of thousands based upon the theory of evolution, which Darwin formulated largely on the strength of observations suggesting that changes in living forms had occurred in the distant past. From an overwhelming body of information—fossil records, the distribution of species over the earth, hybridization, stages of embryo development in higher mammals, the presence of vestigial organs, mutations, the development of domestic breeds through selective breeding—one could infer that evolution of life had occurred. Yet no one in Darwin’s time observed one species changing into another, and Darwin thought that such change might require thousands, perhaps millions, of years.

What most interested Darwin was the driving mechanism behind the alterations. From careful study of the breeding of domestic animals, especially pigeons, he observed that breeders deliberately selected those qualities that they wished to be passed down and bred successfully for them. Breeders of bulldogs reported a similar procedure. It was, on the whole, a simple form of what is now known as genetic engineering. Darwin concluded that in nature something similar occurs. In the competition for life, individuals best adapted to their environment have the best chance of passing their genes on to descendants, a pattern he called natural selection.

The occurrence of natural selection has been documented repeatedly by a succession of studies, the most famous example being cited by Weiner. From the 1930’s through the early 1960’s, northern European cities saw a striking increase in the black mutant form of the peppered moth. The explanation was neither far to seek nor difficult to understand. On city walls and buildings grimed with coal dust and other pollutants, black afforded camouflage from predators. As a result, a higher percentage of mutants survived to reproduce, so that eventually they came to be more populous than the previously dominant lighter form. Following the enactment of environmental laws limiting emissions and promoting the use of natural gas energy, however, the environments became clean and bright once again. Among the moths a decided reversal occurred, so that the lighter form became dominant once again. As with the changes documented by the Grants, decades had to pass before the import of this incidence of natural selection became clear.

The Grants’ extensive study, as yet incomplete, has produced mixed and unexpected findings. The Grants have not witnessed the origin of a new avian species. Thus far, studies of new species have been limited either to those created in laboratories through alteration of DNA or to insect or microscopic life, where reproduction is much more rapid than the once-yearly rate normal for small birds. Nevertheless, the Grants have been able to measure significant changes. Their early assumption that large beaks represent an advantage was dramatically confirmed following drought years in the mid-1970’s. For their diet the birds are dependent upon cactus seeds, and only large, powerful beaks can crack the largest and toughest seeds. In time of scarcity, large beaks proved advantageous, and following a population decline during one severe drought a higher percentage of large-beaked birds survived to breed. When the beaks of their offspring were measured, the result showed a significant increase in average beak size for the entire population.

It was reasonable to assume that in subsequent generations the finches would become ever larger, with ever larger beaks. Yet contrary to expectations, the population reverted toward the previous norm in subsequent years. With the return of above-normal rainfall, an abundance of seeds worked to the competitive advantage of smaller birds with smaller beaks, for they need less food to reach their ideal metabolic level. The larger birds grew too fast for their strength and died off during the droughts that followed. The study established that changing environments alter the demands for successful competition and thus alter the gene pool of a species more rapidly than is commonly thought. During extreme alterations of the environment, the data appear to show, genetic changes in a species can occur quickly.

Through careful observation, the Grants also discovered that hybridization in nature occurs more commonly than has been thought. It has long been believed that hybridization in nature is rare, though it was well understood that animals such as the large felines hybridize rather freely in captivity. Further, it has generally been assumed that hybrid offspring rarely breed successfully themselves. As Weiner demonstrates, the Grants’ project has disproved these assumptions. Not only did the hybrid finches reproduce freely in their natural setting, but the Grants have also concluded that under some conditions hybrids hold a reproductive advantage over nonhybrids. Yet established species do have certain staying powers. The Grants observed the tendency for later generations of hybrids to breed back to nonhybrids and thus to reduce the degree of change while adding to the complexity of the gene pool. Thus there is a kind of regression toward the mean, observable in other wild populations as well.

It is clear that the Grants’ research project, even after more than two decades, is far from complete. Much remains to be done with the mass of data and the DNA analysis. The examination of DNA may finally reveal the still-unknown original progenitor of the finches, if it still exists either on the South American mainland or on some Pacific island.

The research conducted on Daphne Major establishes that natural selection works in the way that Darwin thought but is probably more complicated than he realized. As with domestic breeding governed by deliberate decisions, nature selects traits that endow an individual with an advantage in the struggle for life and passes them on to another generation. Yet the environment, or habitat, is also changing, and the species cannot foresee changes that will occur. In a situation that is drastically altered, new and previously disadvantageous traits may serve to promote survival. The Grants have tentatively concluded that drastic changes in habitat can accelerate the process of species formation, though their observations have not established this as fact.

Weiner’s account of this extensive project illustrates the principle that nature relinquishes its secrets slowly, to only the most committed. It may well be that in the future, long-term studies will be most productive, even as they are the most demanding. The Grants’ project, like Jane Goodall’s study of chimpanzees, represents a lifetime effort that promises to produce more conclusions than the dramatic ones reached thus far. Weiner places it well within the context of evolutionary biology, and he makes the import of such studies clear.

Weiner’s challenges are to make the book interesting to nonscientists, to explain the significance of the subject without becoming too technical or exaggerating that significance. Throughout, for purposes of clarification, he makes comparisons with numerous similar studies. In addition, he injects humor into the narrative, describes characters and their idiosyncrasies, and exploits local-color possibilities of the setting.

Sources for Further Study

Chicago Tribune. June 26, 1994, XIV, p. 7.

Choice. XXXII, November, 1994, p. 483.

The Economist. CCCXXXII, August 13, 1994, p. 80.

Los Angeles Times Book Review. June 19, 1994, p. 2.

Nature. XXXVII, September 1, 1994, p. 27.

New Statesman and Society. VII, September 23, 1994, p. 35.

The New York Times Book Review. XCIX, May 22, 1994, p. 7

Publishers Weekly. CCXLI, April 18, 1994, p. 56.

The Sciences. XXXIV, September, 1994, p. 46.

The Washington Post Book World. XXIV, July 24, 1994, p. 6.

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