Neo-Darwinism After Charles Darwin published his famous theory in 1959, the general concept of evolution gained popularity relatively quickly. However, the process that he suggested was responsible for evolution, natural selection, was not as popular and was met with harsh criticism. Many of his critics thought that the concept of natural selection relied on assumptions about inheritance that could turn out to be false. This happened because Darwin was far ahead of his time and thus was forced to rely on premises about heritability that had not survived empirical tests or scientific rigor. At the time DNA had not been discovered and Darwin had no authority to turn to for an explanation of biological inheritance. Articles written by Gregor Mendel in 1865, which now form the basis for the study of genetics, were revived in 1900 and many thought that Darwin’s theory of natural selection would finally be vindicated. But a funny thing happened. Many of the scientists elaborating on Mendel’s laws of inheritance were concerted anti-Darwinians. The confusion stemmed from the difference between discrete traits and continuous traits. Some heritable traits can be controlled by a single gene (a discrete trait) and others are controlled by the interaction of multiple genes (a continuous trait). Natural selection generally acts on continuous traits, yet Mendel’s laws had not been extended to explain such traits. These “polygenic” traits were much more complicated and so Darwin was not truly vindicated until the 1920s when mathematicians R.A. Fisher, J.B.S. Haldane and Sewall Wright were able to show that continuous traits, the kind that selection acts on, are truly heritable. Their success led to a modern synthesis that combined Mendel’s laws of inheritance along with Darwin’s natural selection and is now referred to as Neo-Darwinism. Since the 1920s the fundamental tenets of Neo-Darwinism have remained intact but much has been contributed. Some of the most notable contributions came from Ernst Mayr who helped to explain how different groups of animals -which were all molded and changed by natural selection- came to become separate species. He suggested that one way that a subpopulation of animals could become separated genetically from an ancestral species is by geographical isolation. Mayr reasoned that if a subpopulation was kept from interbreeding with the species that it came from, whether by a mountain range or a river or great distance, then over time that subpopulation would change in physical appearance and genetic makeup. When different populations of the same species are separated for extended time, they can become reproductively incompatible. It is generally thought that both natural selection and speciation are responsible for the great diversity of life that we see on our planet. To read more about speciation click here. To read more about Darwin's life and work click here. Polygenic: adj. Relating to a characteristic that is determined by the interaction of several genes. Premise: noun A proposition that is used as the basis of an argument or inference. Something assumed. Speciation: noun The evolutionary formation of new biological species, usually by the division of a single species into two or more genetically distinct ones. |
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