THEORIES OF ORIGIN OF LIFE
The major theories accounting for the origin of life on earth are:
1.Life was created by supernatural being at particular time (special creation).
2.Life arose from non living matter on numerous occasions by a process of spontaneous generations.
3.Life has no origin (Steady State)
4. Life arrived on this planet from elsewhere (Cosmozoan).
5.Life arose according to chemical and physical laws (Biochemical Evolution).
Many of these theories and the way they explains the existing diversity of species cover similar ground but with varying emphasis. One of the major areas of controversy,even before the days of Darwin, was the relationship between scientific and theological views on the history of life.
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THE THEORY OF EVOLUTION
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THE THEORY OF EVOLUTION
In terms of living organism, it may be defined as the development of differentiated organisms from pre existing, less differentiated organism over a period of time. The French biologist Lamarck proposed, in 1809 , a hypothesis to account for a mechanism of evolution based on two conditions; the use and disuse of parts, and the inheritance of acquired characteristics .So, according to Lamarckism, as the theory came to be known ,the long neck and legs of the modern giraffe were the result of generation of short necked and short legged ancestors feeding on leaves at progressively higher level of tress. Whilst Lamarck's theory helped prepare the way for acceptance of the concept of evolution, his views on the mechanism of change were never widely accepted.
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Evolution and Natural Selection: 1
In 1859 ,Charles Darwin published the book 'THE ORIGIN OF SPECIES ,that presented a theory to explain how life's diversity came to be.
It has been suggested that without this theory nothing would make much sense in the field of modern biology. Evolution describes the process by which species come to possess genetic adaptations to their environment .Its mechanism is neutral selection. Natural selection acts through individuals by determining which individuals have the best adaptations to guarantee reproductive success. Because the state of environment is always changing temporarily, natural selection is always influencing the genetic characteristics of the population overtime. Thus,natural selection acts to adapt the population to its ever changing surrounds.
It has been suggested that without this theory nothing would make much sense in the field of modern biology. Evolution describes the process by which species come to possess genetic adaptations to their environment .Its mechanism is neutral selection. Natural selection acts through individuals by determining which individuals have the best adaptations to guarantee reproductive success. Because the state of environment is always changing temporarily, natural selection is always influencing the genetic characteristics of the population overtime. Thus,natural selection acts to adapt the population to its ever changing surrounds.
Evolutionary Change is also a change in gene frequency. The pattern of genetic variation changes from one generation to the next generation as natural selection determines which individuals are fittest. New genes enter the species gene pool by way of mutations. By selecting those organism that will become reproductively successful, natural selection controls the future frequency of a population's genes. The appearance of new mutations in a population together with the change in gene frequency results in evolution.
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