Biological Sciences
Darwins Finches
Darwin's finches refer to a group of 15 species of small passerine birds found in the Galápagos Islands. They played a crucial role in Charles Darwin's theory of evolution by natural selection. The variations in beak shape and size among the finches helped Darwin understand how species could adapt to different environments, leading to his groundbreaking ideas on evolution.
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8 Key excerpts on "Darwins Finches"
eBook - PDFGood Enough
The Tolerance for Mediocrity in Nature and Society
- Daniel S. Milo(Author)
- 2019(Publication Date)
- Harvard University Press(Publisher)
What struck Darwin, and the successors who made the finches symbolic of Darwinism, was the specialization manifest in the various species’ differently shaped beaks. On one island, abundant in nuts and seeds, the finches had large, rounded beaks suited to breaking and milling. On another, abundant in grubs 74 icons as test cases and insects, the finches had elongated, slender beaks suited to snagging a wriggling meal. Darwin speculated that the finch spe-cies descended from a common ancestor based on the South American continent and were modified to better accomplish the task of feeding in their new homes. He suspected that the sepa-rate species arose in isolation on the assorted islands of the ar-chipelago. But he did not infer the theory of evolution by natural selection from the finch encounter, which receives vir-tually no attention in the Origin. As we saw in Chapter 2, natural selection was not really induced; rather, it was, deduced from the analogy to artificial selection. Still, the Gal á pagos finches greatly informed his thinking, as discussed in his Journal of Re-searches (1839, revised 1845), which eventually became known as The Voyage of the Beagle . The later theorists who elevated the finch’s status did fine, even awe-inspiring, scientific work. But aggressive marketing and careless intellectual history distort their findings into apparent validation of Darwin’s overbroad assertions concerning the preva-lence of natural selection. In fact, more recent science has shown only—beautifully, rigorously—that natural selection explains speciation of what have become known since Lack’s book as Dar-win’s finches. This research does not demonstrate that variations are, in general, selected because they confer adaptive advan-tage. It proves the selected character of the finch beak, not that everything else in nature, or even most of it, is also selected. Too many have extrapolated too much from the finches.
- Michael Ruse(Author)
- 2013(Publication Date)
- Cambridge University Press(Publisher)
G 36 8 g G E s say 4 5 g Darwin and the Finches Frederick Rowe Davis L ike many other naturalists, Charles Darwin did not find the finches to be very interesting. During his five-week visit to the Galapagos Islands, Darwin saw many finches and collected some of them, but they were so dif- ferent in outward appearance that he failed to recognize that they all came from the same family. Instead, he initially called one a finch, another a blackbird, and another a grosbeak. After his return to England, the ornithologist John Gould (1839), who ana- lyzed and described Darwin’s ornithological collection, convinced Darwin that the finches merited more interest. In the first edition of the Voyage of the Beagle (1839), Darwin noted the similarities among the finches (see Plate XXXIV). The biological importance of the finches had made an impression on Darwin in the years since his brief encounter with them: “These birds are the most singular of any in the archipelago,” but in most respects of form and function, they remained uninteresting. Nevertheless, the beaks of the various species did capture Darwin’s (1839c) attention: “It is very remarkable that a nearly perfect gradation of struc- ture in this one group can be traced in the form of the beak, from one exceeding in dimensions that of the largest gros-beak, to another differing but little from that of a warbler.” Darwin returned to the possible implications for natural history of this “nearly perfect gradation of structure” later in his account of the wildlife of the Galapagos, and he tentatively suggested that the different finches may have been confined to different islands; unfortunately, he failed to label his specimens to island (Sulloway 1982a, 1984). Darwin visited five islands of the Galapagos, but the captain and crew of HMS Beagle conducted hydrogeographic surveys of most of the islands, and Darwin drew upon their natural history collections also.
eBook - PDFHistory of Modern Psychology
A Global Perspective
- C. James Goodwin(Author)
- 2023(Publication Date)
- Wiley(Publisher)
(Darwin, 1859/1958b, p. 74, p. 88) 8 It is usually reported that all 1250 copies of the first print run sold out on the opening day of sales, but those books were all sold to booksellers, not to the general public; although the book soon attracted the public’s attention, the impression of people making a mad dash to bookstores on the first day of sales is misleading (Reel, 2013). CHARLES DARWIN (1809–1882) AND THE THEORY OF EVOLUTION 139 Darwin’s finches illustrate the manner in which the struggle for existence and natural selection combine to alter species. Darwin believed that the original finches arrived as a single species from the mainland and settled in the various islands of the Galapagos. Because there is variation among members of a species in the wild, slight differences from one finch to another existed, including variations in beak shape. Suppose some of the birds happened to land on islands rich in certain types of seeds that are encased in hard shells. Those finches with slightly tougher and more blunted beaks would have an advantage in the hunt for these seeds. Finches with slightly thinner beaks would have a more difficult time getting at the seeds and would be more likely to die. Hence, the finches with the more “adaptive variation” would be “naturally selected” in the “struggle for existence.” They would survive and pass on the advantage to their offspring. Over time, finches on that particular island would form a new species characterized by the specific beak shape. Similarly, on another island rich in insects, a species of finch with beaks thin enough to reach into small spaces would evolve. Darwin believed that evolution by natural selection also explained extinction and the reason why modern species resemble fossils of extinct species found in the same geographical region. In South America, for example, Darwin had uncovered fossilized bones of animals similar to modern llamas but two to three times as large.
eBook - PDF- C. James Goodwin(Author)
- 2022(Publication Date)
- Wiley(Publisher)
Over time, finches on that island would form a new species character- ized by the specific beak shape. Similarly, on another island rich in insects, a species of finch with beaks thin enough to reach into small spaces would evolve. 8 It is usually reported that all 1250 copies of the first print run sold out on the opening day of sales, but those books were all sold to booksellers, not to the general public; although the book soon attracted the public’s attention, the impression of people making a mad dash to bookstores on the first day of sales is misleading (Reel, 2013). 124 CHAPTER 5 DARWIN’S CENTURY: EVOLUTIONARY THINKING Darwin believed that evolution by natural selection also explained extinction and the reason why modern species resemble fossils of extinct species found in the same geographical region. In South America, for example, Darwin had uncovered fossilized bones of animals like modern llamas but two to three times as large. Over time, he argued, the larger species had encountered environmental events (e.g., droughts) that reduced the food supply and favored the survival of smaller variations that did not need as much food. In the remaining chapters of the Origin, Darwin described evidence in support of his theory and tried to answer the objections he knew would be forthcoming. He recognized that most people believed in the divine creation of every single species but asked his readers to consider the evidence he had placed before them. After the Origin of Species Reaction to Darwin’s theory was not long in coming, the theory a direct refutation to the argument from design and therefore a clear threat to the Church of England. In the debates over evolution, Darwin himself stayed above the fray, preferring to have his case argued by others. One such ardent Darwinian was Thomas Huxley (1825–1895), who became known as “Darwin’s bulldog” (Browne, 2002).
eBook - PDF- Robert Jurmain, Lynn Kilgore, Wenda Trevathan, Russell Ciochon(Authors)
- 2017(Publication Date)
- Cengage Learning EMEA(Publisher)
The 13 species of Galápagos finches are presumably all descended from a common ancestor that lived on the South American mainland. Thus, they illustrate the role of geographical isolation. Before Darwin, individual members of species were not considered important, so they weren’t the focus of research. But as we’ve seen, Darwin recognized the uniqueness of individuals and realized that variation among them could explain how selection occurs. Favorable variations are selected, or chosen, for survival by nature; unfavorable ones are eliminated. Natural selection operates on individu-als , either favorably or unfavorably, but it’s the population that evolves . It is impor-tant to emphasize that the unit of natural selection is the individual; the unit of evolution is the population. This is because individuals don’t change genetically but, over time, populations do. Natural Selection in Action One of the most frequently cited examples of natural selection relates to changes in the coloration of a species of peppered moth. In the 1990s, the peppered moth fitness Pertaining to natural selection, a measure of the relative reproductive success of individuals. Fitness can be mea-sured by an individual’s genetic contribu-tion to the next generation compared with that of other individuals. The terms genetic fitness, reproductive fitness , and differential net reproductive success are also used. reproductive success The number of offspring an individual produces and rears to reproductive age, or an indi-vidual’s genetic contribution to the next generation. selective pressures Forces in the envi-ronment that influence reproductive suc-cess in individuals. Copyright 2018 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-300 CHAPTER 2 | THE DEVELOPMENT OF EVOLUTIONARY THEORY 40 story came under criticism, mainly due to issues with the original research design of the 1950s experiments.
eBook - PDFDarwin and Design
Does Evolution Have a Purpose?
- Michael Ruse, Michael RUSE(Authors)
- 2009(Publication Date)
- Harvard University Press(Publisher)
far from land. Thanks to the governor, who pointed out that the giant tortoises indigenous to the archipelago are different from island to is-land, Darwin came to see that this variation held true of other fauna— the finches and mockingbirds in particular, which were peculiar to their specific island homes. This fact had to be important, especially since the various birds on the islands somewhat resembled birds on the South American mainland. On the continent Darwin had seen evidence of the same birds inhabiting sites from the steamy jungles of Brazil in the north to the snowy deserts of Patagonia in the south. But it was not until he re-turned to England that he understood the significance of these differ-ences. Darwin showed his collection to the leading ornithologist of the day, John Gould, who determined that the Galápagos birds represented different species. With that information, Darwin made the big leap to evolution: the only way the differences could be explained was through descent with modification. This became the central fact of evolution in Darwin’s work. Darwin was never that focused on questions about the path of evolution (phylog-eny)—on tracing which specific animal or plant groups descended from which other groups. After the Galápagos experience, he always thought of the path of evolution as being tree-like, with an original stem that branched up to the present. What was of greater concern to Darwin was the cause or causes of evolution. Without causes, he was no more than one among many evolutionists. With causes, he might become the New-ton of biology. As a graduate of the University of Cambridge (Newton’s alma mater) and a friend and protégé of Whewell, Darwin knew full well that the best kind of science is that which has a cause at its heart, one which ties all to-gether in a unified whole.
eBook - PDFThe Annotated Origin
A Facsimile of the First Edition of On the Origin of Species
- Charles Darwin(Author)
- 2009(Publication Date)
- Belknap Press(Publisher)
Darwin seemed to see the significance of these birds, but he did not yet realize that the finches of those equatorial islands were even more remarkable, nor that the tortoises told a similar story. Nonetheless, crucial data came to Darwin almost as a revelation when, in London and Cambridge, specialists impressed upon him the curious nature of his collections from South America and the Galápagos. Winter and spring of 1837 was a watershed period in Dar-win’s thinking. The Beagle arrived home on October 2, 1836, and Darwin wasted no time seeing family and friends and mak-ing arrangements to distribute his biological collections for study. He took up residence in Cambridge in mid-December, on Fitzwilliam Street, where he stayed through March. He twice trekked back to London during this time to attend scientific meetings and confer with friends and colleagues. Much hap-pened in those heady months, particularly in connection with his fossil discoveries from South America and the Galápagos avifauna. Darwin delivered his fossil mammal specimens to Richard Owen in late December or early January, and within a month the great anatomist knew that they were remarkable. Owen said as much in a letter to Charles Lyell dated January 23, in which he revealed that Darwin had discovered no fewer than five extinct relatives of mammals found in South America today— and moreover, that these extinct species were gigantic forms: a massive armadillo, a giant sloth, a tank-like armored sloth rel-ative, a rodent with a skull more than two feet long, dwarfing all living rodents; and a llama so large that Darwin had tenta-tively labeled its bones those of a mastodon! (Herbert 2005, pp. 320–324). Something profound was happening, and Owen knew it. Darwin’s finds confirmed the “law of succession,” which described the replacement of so-called types by related, though distinct, forms through geological time.
eBook - PDF- David Kohn(Author)
- 2014(Publication Date)
- Princeton University Press(Publisher)
This highlighting of a known idea took place just as other key results of the voyage were coming into focus, and it was, after all, the integration of such widely different classes of data into a new synthesis that became Darwin's role. The third class of data growing out of the zoologists' processing of the Beagle specimens has to do with the issue of representative species. Darwin THE DARWINIAN HERITAGE revealed some awareness of this idea in his celebrated ornithological notebook in a passage (now dated by Sulloway as written June or July 1836) mainly on the birds of the Galapagos, but also mentioning the foxes of the Falkland Islands. Darwin was struck by the point that organisms "slightly differing in structure and filling the same place in Nature" could be found in different places. But that famous note remains ambiguous, in good part because Darwin injected the phrase, "I must suspect they are only varieties." Only if this suspicion was removed would "such facts . . . undermine the stability of species." The suspicion was not alleviated until early 1837, when the zoological results of the voyage poured in. Extended over a wider scale, Darwin's intuition (as against his prudent "suspicion") was richly confirmed. At a taxonomic level higher than species, there is a broad pattern of resemblances between the forms found in neighboring regions. The greater their isolation from each other — in time, reinforced by space and other barriers — the greater the differences. But islands typically have a general relation of similarity to nearby continents in their flora and fauna. In the Red Notebook, this idea is conveyed in an odd phrase: ". . . new creation affected by Halo of neighboring continent ..." (RN 127, written mid-March, 1837). In one possible reading, Darwin is suggesting that a geographic region somehow imposes a character on its organic productions.
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