Evolution

In biology, evolution is the process by which populations of organisms acquire and pass on novel traits from generation to generation, affecting the overall makeup of the population and even leading to the emergence of new species.

History of evolutionary thought

The idea of biological evolution has existed since ancient times, notably among Hellenists such as Epicurus, but the modern theory was not established until the 18th and 19th centuries, by scientists such as Jean-Baptiste Lamarck and Charles Darwin. While transmutation of species was accepted by a sizeable number of scientists before 1859, it was the publication of Charles Darwin's The Origin of Species which provided the first cogent mechanism by which evolutionary change could occur: his theory of natural selection. Darwin was motivated to publish his work on evolution after receiving a letter from Alfred Russel Wallace, in which Wallace revealed his own discovery of natural selection. As such, Wallace is sometimes given shared credit for the theory of evolution.

Related Topics:
Epicurus - Jean-Baptiste Lamarck - Charles Darwin - 1859 - The Origin of Species - Alfred Russel Wallace

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Darwin's theory, though it succeeded in profoundly shaking scientific opinion regarding the development of life, could not explain the source of variation in traits within a species, and Darwin's proposal of a hereditary mechanism (pangenesis) was not compelling to most biologists. It was not until the late 19th and early 20th centuries that these mechanisms were established.

Related Topics:
Hereditary - Pangenesis

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When Gregor Mendel's work regarding the nature of inheritance in the late 19th century was "rediscovered" in 1900, it led to a storm of conflict between Mendelians (Charles Benedict Davenport) and biometricians (Walter Frank Raphael Weldon and Karl Pearson), who insisted that the great majority of traits important to evolution must show continuous variation that was not explainable by Mendelian analysis. Eventually, the two models were reconciled and merged, primarily through the work of the biologist and statistician R.A. Fisher. This combined approach, applying a rigorous statistical model to Mendel's theories of inheritance via genes, became known in the 1930s and 1940s as the modern evolutionary synthesis.

Related Topics:
Gregor Mendel - 19th century - 1900 - Charles Benedict Davenport - Walter Frank Raphael Weldon - Karl Pearson - R.A. Fisher - 1930s - 1940s - Modern evolutionary synthesis

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In the 1940s, following up on Griffith's experiment, Avery, McCleod and McCarty definitively identified deoxyribonucleic acid (DNA) as the "transforming principle" responsible for transmitting genetic information. In 1953, Francis Crick and James Watson published their famous paper on the structure of DNA, based on the research of Rosalind Franklin and Maurice Wilkins. These developments ignited the era of molecular biology and transformed the understanding of evolution into a molecular process: the mutation of segments of DNA (see molecular evolution).

Related Topics:
1940s - Griffith's experiment - Avery - McCleod - McCarty - Deoxyribonucleic acid (DNA) - 1953 - Francis Crick - James Watson - Rosalind Franklin - Maurice Wilkins - Molecular biology - Mutation - Molecular evolution

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George C. Williams' 1966 Adaptation and natural selection: A Critique of some Current Evolutionary Thought marked a departure from the idea of group selection towards the modern notion of the gene as the unit of selection. In the mid-1970s, Motoo Kimura formulated the neutral theory of molecular evolution, firmly establishing the importance of genetic drift as a major mechanism of evolution.

Related Topics:
George C. Williams - 1966 - 1970s - Motoo Kimura - Neutral theory of molecular evolution - Genetic drift

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Debates have continued within the field. One of the most prominent public debates was over the theory of punctuated equilibrium, proposed in 1972 by paleontologists Niles Eldredge and Stephen Jay Gould to explain the paucity of transitional forms between phyla in the fossil record.

Related Topics:
Punctuated equilibrium - 1972 - Paleontologists - Niles Eldredge - Stephen Jay Gould

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