Theory of Evolution (II)
Lamarck argued that new organs arise from new necessities, and that existing organs change adaptively. An organ disappears if it is not used. In Lamarck's view, the weight-lifter's son should be born with muscles bigger than the usual, which modern genetic studies have proved that is incorrect. Characteristics acquired during the life of a person are not transmitted to his sons. Lamarck published his theory in 1809 in his book "Zoological Philosophy." He was also the first to distinguish between vertebrates and invertebrates.
The theory of evolution that is accepted nowadays was proposed simultaneously by Charles Darwin (1809-1882) and Alfred Russel Wallace, but it is usually credited to the former because he could have proposed it earlier had it not been by his more than twenty years of study. Although Darwin had been urged by his scientific friend to publish his findings, he refused to do so until he knew of Wallace's work, which was much less complete than his. It was then decided to present both works at a single meeting of the Linnaean Society of London in 1858.
Darwin was influenced by the English clergyman Thomas R. Malthus, who proposed that environmental factors such as famine and disease could prevent the growth of a population. Darwin realized that this could be applied to all living species, and that a heritable change in an animal could influence its offspring's outcome. His book "On the Origin of Species by Means of Natural Selection," published in 1859, presented a definition of evolution. It explained that natural selection is a process that operates spontaneously in nature. Darwin pointed out that many animal species are subject to variations, and that these variations may make some of them more fit to some ecological conditions. Their increased possibilities of surviving make their descendants more numerous, and over the passage of time they displace other less apt variations.
What Darwin never understood--and nobody knew at his time--was how variations occurred and how they were transmitted. It was left to the modern science of genetics to answer these questions. The principles of heredity--the basis of genetics--were laid by the monk Gregor Mendel in 1865, but they were not known to Darwin and, indeed, they were little known until the 20th century. Once genetics was evolved, the theory of evolution gained new impulse although some of Darwin's ideas were found to be incorrect. In addition to explaining how heredity functions, genetics has shown that variations in species occur by means of mutation and genetic recombination. The modern theory of evolution is known as the synthetic theory.
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