Introduction To Evolution
What is Evolution? Evolution is the process by which all living things have developed from primitive organisms through changes occurring over billions of years, a process that includes all animals and plants. Exactly how evolution occurs is still a matter of debate, but there are many different theories and that it occurs is a scientific fact. Biologists agree that all living things come through a long history of changes shaped by physical and chemical processes that are still taking place. It is possible that all organisms can be traced back to the origin of Life from one celled organims.
The most direct proof of evolution is the science of Paleontology, or the study of life in the past through fossil remains or impressions, usually in rock. Changes occur in living organisms that serve to increase their adaptability, for survival and reproduction, in changing environments. Evolution apparently has no built-in direction purpose. A given kind of organism may evolve only when it occurs in a variety of forms differing in hereditary traits, that are passed from parent to offspring. By chance, some varieties prove to be ill adapted to their current environment and thus disappear, whereas others prove to be adaptive, and their numbers increase. The elimination of the unfit, or the "survival of the fittest," is known as Natural Selection because it is nature that discards or favors a particular being. Evolution takes place only when natural selection operates on apopulation of organisms containing diverse inheritable forms.
Pierre Louis Moreau de Maupertuis (1698-1759) was the first to propose a general theory of evolution. He said that hereditary material, consisting of particles, was transmitted from parents to offspring. His opinion of the part played by natural selection had little influence on other naturalists.
Until the mid-19th century, naturalists believed that each species was created separately, either through a supreme being or through spontaneous generation the concept that organisms arose fully developed from soil or water. The work of the Swedish naturalist Carolus Linnaeus in advancing the classifying of biological organisms focused attention on the close similarity between certain species. Speculation began as to the existence of a sort of blood relationship between these species. These questions coupled with the emerging sciences of geology and paleontology gave rise to hypotheses that the life-forms of the day evolved from earlier forms through a process of change. Extremely important was the realization that different layers of rock represented different time periods and that each layer had a distinctive set of fossils of life-forms that had lived in the past.
Jean Baptiste Lamarck was one of several theorists who proposed an evolutionary theory based on the "use and disuse" of organs. Lamarck stated that an individual acquires traits during its lifetime and that such traits are in some way put into the hereditary material and passed to the next generation. This was an attempt to explain how a species could change gradually over time. According to Lamarck, giraffes, for example, have long necks because for many generations individual giraffes stretched to reach the uppermost leaves of trees, in each generation the giraffes added some length to their necks, and they passed this on to their offspring. New organs arise from new needs and develop in the extent that they are used, disuse of organs leads to their disappearance. Later, the science of Genetics disproved Lamarck's theory, it was found that acquired traits cannot be inherited.
Thomas Robert Malthus, an English clergyman, through his work An Essay on the Principle of Population, had a great influence in directing naturalists toward a theory of natural selection. Malthus proposed that environmental factors such...
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