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EVOLUTION (BIOL 4100 / 6100)
Essay #1 Study Guide
The following material represents the type of questions I will ask for Essay #1 from The Beak of the Finch. This is a study guide and not a list of questions that will be on the essay. The essay exam will consist of 5-7 questions. As is indicated in the syllabus, the essay exam will be completed in class on Thursday 12 October. Essay exams are scored from a maximum of 50 points.
1. Explain why Daphne Major is / has been a particularly good place to study natural selection.
Daphne Major is an island part of the archipelago Colon, commonly known as the Galapagos Islands. The Galápagos Islands have species found in no other part of the world, though similar ones exist on the west coast of South America. Darwin was struck by the fact that the birds were slightly different from one island to another. He realized that the key to why this difference existed was connected with the fact that the various species live in different kinds of environments.
The Galapagos Islands are about 1,000 km (600 miles) off the west coast of South America. When Charles Darwin arrived there in 1835 during his voyage on the HMS Beagle, he discovered many species not found anywhere else in the world—for example, several species of finches, of which 14 are now known to exist (called Galapagos, or Darwin's, finches). These passerine birds have adapted to a diversity of habitats and diets, some feeding mostly on plants, others exclusively on insects. The various shapes of their bills are clearly adapted to probing, grasping, biting, or crushing—the diverse ways in which the different Galapagos species obtain their food. The explanation for such diversity is that the ancestor of Galapagos finches arrived in the islands before other kinds of birds and encountered an abundance of unoccupied ecological niches. Its descendants underwent adaptive radiation, evolving a variety of finch species with ways of life capable of exploiting opportunities that on various continents are already exploited by other species.
Among the birds that ended up in arid environments, the ones with beaks better suited for eating cactus got more food. As a result, they were in better condition to mate. Similarly, those with beak shapes that were better suited to getting nectar from flowers or eating hard seeds in other environments were at an advantage there. In a very real sense, nature selected the best adapted varieties to survive and to reproduce. This process has come to be known as natural selection.
Darwin did not believe that the environment was producing the variation within the finch populations. He correctly thought that the variation already existed and that nature just selected for the most suitable beak shape and against less useful ones. Some of Darwin's supporters ultimately described this process as the "survival of the fittest." This is very different from Lamarck's incorrect idea that the environment altered the shape of individuals and that these acquired changes were then inherited.
Natural selection acts through the size of food items that are available. This was the most important factor determining beak size for each population. If there are only large food items available, birds with large beaks can crack them better and thus survive better. To the contrary, if the seed size is very small, then small birds survive better. During the current study, large birds survived better.
None of what follows is meant to detract from the dedicated fieldwork of the Grants, whose incredibly detailed measurements of thousands of birds over a 20-year period on the small island of Daphne Major are a major contribution to the study of population dynamics and ecology.
2. Discuss why Darwin used observations from mockingbirds, instead of finches, on the Galápagos Islands to develop his early ideas on natural selection.
Darwin used observations from mockingbirds, instead of finches, on the Galápagos Islands to develop his early ideas on natural selection. It could be said that ornithological activities in Galápagos began with the collection Charles Darwin made of 15 species of birds while he visited the archipelago in 1835. Darwin noticed some morphological differences between the mockingbirds inhabiting various islands.
Nevertheless, the historical record is not very clear in determining what he thought about the finches subsequently named for him. What we do know is that Darwin would come to understand the importance of the species he collected, above all the finches, and several years later. On the basis of this and other knowledge that he acquired during his trip around the world, he came to formulate the theory of evolution of species by means of natural selection. Darwin was busy conducting scientific research that would bolster his observations of the finches and mockingbirds of the Galpagos Islands.
On the Galápagos Islands Darwin found that mockingbirds differed from one island to another, and on returning to Britain he was shown that Galápagos tortoises and finches were also in distinct species based on the individual islands they inhabited.The thinking was rooted in observations Darwin made as he traveled around the world from 1831 to 1836, in the role of ship's naturalist aboard the Beagle. Pondering variations among Galapagos mockingbirds, he began considering the evolution of species, writing in his notebook.
Finally, Darwin's observations of both the mockingbirds and the finches proved important in the later development of his theory of natural selection. After all, why were there four species of mockingbirds spread throughout the islands; what role could each individual species serve, and why were each confined to certain geographical locations? During his time on the Galápagos, these questions were too intriguing to let go, and Darwin collected samples later analyzed by the noted ornithologist J. Gould. Darwin also proceded to collect finch species, and Gould was later able to identify the 13 related species. Within the 13 species, the gradation of the size of the beaks of the birds provided Darwin with evidence for multiple species descended from a single ancestor. Later, the territorial uniqueness of the birds on certain islands brought forth the means for such speciation via geographical separation and diversification. Certainly, the finches (and to a less common extent, the mockingbirds) remain the epitome of Darwinian evolution.
Mockingbirds found on different islands only a few miles apart were different from each other. All the mockingbirds in the Galapagos Islands, on the other hand, were also similar to the mockingbirds of South America six hundred miles to the east-and yet different-different enough to be a different species. Apart from the ubiquitous finches the mockingbirds are among the most obvious of the small land birds of the impoverished Galapagos avifauna. They have been considered sufficiently distinct from other mockingbirds to be placed in a separate genus, Nesomimus.
3. Discuss the contributions of Charles Lyell to the development of Darwin's ideas on natural selection.
Publication of the 1st volume of Charles Lyell's is PRINCIPLES OF GEOLOGY (1830-1833). Charles lyell's work would greatly influence the young charles Darwin. It would help put emphasis on the interpretation of the biblical story of genesis as fabular and metaphorical, rather than as literally historic.
On the voyage, Darwin read Charles Lyell's Principles of Geology, which explained geological features as the outcome of gradual processes over huge periods of time, and wrote home that he was seeing landforms "as though he had the eyes of Lyell": he saw stepped plains of shingle and seashells in Patagonia as raised beaches; in Chile, he experienced an earthquake and noted mussel-beds stranded above high tide showing that the land had been raised; and even high in the Andes, ...
Evolution questions regarding the book the break of the finch is determined.