Biology came of age on November 24, 1859, the day Charles Darwin published On The Origin of Species by Means of Natural Selection. His book presented the first convincing case for evolution and led the way in the emergence of biology from a bewildering chaos of facts into a cohesive science. In biology, evolution refers to all the changes that have transformed life on Earth from its earliest beginnings to the seeningly infinite diversity that characterizes it today. Darwin addressed the sweeping issues of biology: the great diversity of organisms, their origins and relationships, their similarities and differences, their geographical distribution, and their adaptations to the surrounding environment. Darwin made two points in The Origin of Species. First, he argued from the evidence that species were not specifically created in their present forms, but had evolved from ancestral species.
Second, Darwin described a mechanism for evolution, which he termed natural selection. Evolutionary change is based mainly on the interactions between populations of organisms and their environments. The Origin of Species was truly radical, for not only did it challenge prevailing scientific views, but it also shook the deepest roots of Western culture. Darwins view of life contrasted sharply with the conventional paradigm of an Earth only a few thousand years old, populated by immutable (unchanging) forms of life that had been individually made by the Creator during the single week in which he formed the entire universe. Darwins ideas subverted a world view that had been taught for centuries. THE VOYAGE OF THE BEAGLE — Darwin was 22 years old when he sailed from England with the Beagle in December 1831. The primary mission of the voyage was to chart poorly known stretches of the South American coastline. While the crew of the ship surveyed the coast, Darwin spent most of his time on shore, collecting thousands of specimens of the exotic and exceedingly diverse fauna and flora of South America. As the ship worked its way around the continent, Darwin was able to observe the various adaptations of plants and animals that inhabited such diverse environments as the Brazilian jungles, the expansive grasslands of the Argentine pampas, the desolate lands of Tierra del Fuego near Antartica, and the towering heights of the Andes Mountains.
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He realized that the fauna and flora were very distinct from the life forms of Europe. The plants and animals living in temperate regions of South America were taxonomically closer to species living in tropical regions of that continent than to species in temperate regions of Europe. Furthermore, the South American fossils that Darwin found, though clearly different from modern species, were distinctly South American in their resemblance to the living plants and animals of that continent. Darwin was perplexed by the peculiarities of the geographical distribution of species. A particularly puzzling case of geographical distribution was the fauna of the Galapagos Islands, which lie on the Equator about 900 km. west of the South American coast.
Most of the animal species on the Galapagos live nowhere else in the world, although they resemble species living on the South American mainland. Among the birds Darwin collected on the Galapagos were 14 types of finches that, although quite similar, seemed to be different species. Some were unique to individual islands, while other species were distributed on two or more islands that were close to each other. Darwin wondered about the relationships of the island finches to one another and to the finches on the mainland, which were different. By the time the Beagle sailed from the Galapagos, Darwin had read Lyells Principles of Geology. Darwin was doubting the churchs position that the Earth was static and had been created only a few thousand years ago.
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By acknowledging that the Earth was very old and constantly changing, Darwin had taken an important step toward recognizing that life on Earth had also evolved. He would soon realize that evolution was the only rational explanation for the relationships between the species he had collected, particularly those from the Galapagos Islands. At the time Darwin collected the Galapagos finches, he was not sure whether they were actually different species or merely varieties of a single species. Soon after returning to England in 1836, he learned from ornithologists (bird specialists) that the finches were indeed separate species. He began to reassess all that he had observed during the voyage of the Beagle and in 1837 began the first of several notebooks on the origin of species. Darwin began to perceive the origin of new species and adaptation as closely related processes.
A new species would arise from an ancestral form by the gradual accumulation of adaptations to a different environment. For example, if one species became fragmented into several localized populations isolated in different environment by geographical barriers, the populations would diverge more and more in appearance as each adapted to local conditions, gradually, over many generations, becoming dissimilar enough to be designated separate species. This is apparently what happened to the Galapagos finches. Among the differences between the birds are their beaks, which are adapted to the specific foods available on their home islands. Darwin anticipated that explaining how such adaptations arise was essential to understanding Bibliography 1. Biology by Neil A. Campbell C.1986