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Cambrian Explosion - Research Paper Example

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Cambrian Explosion The term Cambrian refers to period in the earth’s history roughly estimated as being between 543 and 490 million years ago. The name Cambrian derives from the discovery of the first fossils from this era by British geologist Adam Sedgwick in a part of Wales called the Cambrian Hills…
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Cambrian Explosion

Download file to see previous pages... Parker defines it thus: “The Cambrian explosion is the evolutionary episode in which all animal phyla attained complex external forms.” (Parker, 2003, p. 9) The phylum is the body plan of an animal, and in the period before 543 million years ago, called the Precambrian era, there were only three distinct animal phyla, whereas at 538 million years ago, there were 38, and this phenomenal increase is what gives rise to the term “Cambrian explosion.” Some aspects of this theory are, however, disputed, and there are studies which support a much more gradual development of the 38 animal phyla over a much longer time, reaching back long before the so-called explosion period from 543 million years ago. This paper examines the key arguments in favour and against the phenomenon known as the Cambrian explosion concludes with some reflection on what the implications of the Cambrian explosion debate are for modern science. Most scholars agree that there is a step-change in the fossil record at around 543 million years ago. There are some problems, however, in assuming that this surviving record showing a sudden increase in phyla variation gives us a true and complete picture of what actually happened. As scientists discover and analyse further samples, and as new technologies emerge which allow different kinds of analysis, the picture can change dramatically. Above all, it must always be remembered that the preservation of specimens is largely a matter of chance, and there is always the possibility that key pieces of evidence have not survived, or have not yet been discovered: “While fossils provide the only tangible evidence for the origin of animals, some key early metazoan fossils are rare and many lack informative characters, making the derivation of a rigorous phylogenetic hypothesis based solely on fossil data difficult.” (Cartwright and Collins, 2007) Referring to new technologies such as comparative genomics , Cartwright and Collins conclude that “currently available genomic data supports the origin of a complex genome predating the Cambrian radiation, with the ancestral genome possessing the molecular toolkit necessary for an ‘explosion’ of body plans and complex traits.” (Cartwright and Collins, 2007) This position modifies the theory of the Cambrian explosion only slightly, since it theorizes a large number of evolutionary changes before 543 million years ago, at the molecular level, which then had the effect of causing a rapid divergence of organisms in the Cambrian explosion period. Factors external to the animals then prompt the adaptations that we see in the physical record. Some of the more popular science books propose single factors as “triggers” for the Cambrian explosion, such as changes in the way that light affected the earth which in turn prompte the evolution of sight, which had the effect of increasing pressure on organisms to avoid being seen and eaten by other organisms (Parker, 2003). The importance of the Burgess shale deposits in British Columbia, Canada is recognized as a crucial piece of evidence and has been labelled as the indicator of a “Big Bang” in animal evolution. (Carroll, 2005, p. 138) The diversity of forms is explained in terms of adaptation to changes in the environment: “Genes in the tool kit are important actors in this picture, but the tool kit itself represents only possibilities, not destiny. The drama of the Cambrian was driven by ecology on a global ...Download file to see next pagesRead More
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