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Theories to explain the apparent evolution of living things Two theories were proposed which we can now see are attempts to evade the available evidence: Catastrophism and Lamarkianism. Catastrophism suggested that species were indeed immutable (unchanging), but that they many species have been lost over the history of the Earth. Catastrophes which happened during that history at certain times eliminated large numbers of species, which appear in the fossil record to be succeeded by new species. Catastrophism suggests that this is not the case, and that instead pre-existing organisms which survived the catastrophe simply populated the world afterward The fossil record refutes this theory since it is quite clear that fossil forms from more recent layers are utterly absent from earlier layers, despite the vast amount of material available from each layer. Lamarkianism attempts a different explanation for change over time, that individual organisms adapt to their environment, and that the changes made are then passed on to their descendants. There is in fact no evidence for this theory. Neo-Lamarkianism in the Soviet Union during the 1930s essentially destroyed Soviet genetics, and helped to destroy Soviet agriculture. Darwinism Charles Darwin was a trained minister of the Church of England, who was an avid naturalist. His observations of nature during a five year voyage on H.M.S. Beagle led him to propose the theory which continues to define biological thought in the 20th century. Darwin was heavily influenced by those naturalists who had preceded him, and certainly had absorbed the ideas of the changing nature of species on earth. His contribution to biology boils down to his proposing a mechanism which could explain this evolution, not the process of evolution itself. He was also strongly influenced by the writings of Thomas Malthus who wrote that human populations tend to grow exponentially, and to outstrip the available food resources--this leads to crises in which individuals compete strongly for the limiting supply of food. Darwin generalized this theory to all populations. Darwin's insight was that variations in the hereditary traits of the members of these populations might affect their ability to compete for resources Darwin found evidence for the effects of competition driving evolution of animals in the Galapagos Islands off Ecuador. As is often the case on islands, the Galapagos have a unique population of animals and plants. Darwin argued that the availability of food would "select" for adaptive changes in populations. For example, in a population of birds presented only with very hard seeds those with the strongest bills will tend to be able to survive and reproduce best since they will be able to forage better than those with weaker bills Darwin, and later Alfred Wallace, described a theory which explained the changing nature of species. Given the Malthusian tendency to outstrip resources individuals in a population must compete for those resources. Since the individuals differ in their "form and function", and these differences can affect the ability of the individuals to compete for the resources. Adaptive traits (traits which confer a greater ability to compete) must increase in frequency over successive generations. Therefore, populations can evolve because of this natural selection the traits which characterize the population can change over time when heritable traits are responsible for differences in survival and reproduction. Darwin's and Wallace's explanation for how evolution occurred is now considered to be inaccurate. Many evolutionists, but not all, consider it likely that evolution is a much more chaotic process. Species survive mass extinctions more by luck than because of adaptive traits, under this hypothesis. The field of evolutionary theory is still in ferment, though this does not mean that biologists disbelieve the underlying reality of evolution as a process.. |
Copyright © Philip Farabaugh 2000