EVOLUTION

Topics: Evolution, Genetics, DNA Pages: 14 (4102 words) Published: February 23, 2014
This article is about evolution in biology. For other uses, see Evolution (disambiguation). Page semi-protected
For a generally accessible and less technical introduction to the topic, see Introduction to evolution. Part of a series on
Evolutionary biology
Diagrammatic representation of the
divergence of modern taxonomic
groups from their common ancestor.
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History of evolutionary theory[show]
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Evolution is the change in the inherited characteristics of biological populations over successive generations. Evolutionary processes give rise to diversity at every level of biological organisation, including species, individual organisms and molecules such as DNA and proteins.[1]

All life on Earth is descended from a last universal ancestor that lived approximately 3.8 billion years ago. Repeated speciation and the divergence of life can be inferred from shared sets of biochemical and morphological traits, or by shared DNA sequences.[2] These homologous traits and sequences are more similar among species that share a more recent common ancestor, and can be used to reconstruct evolutionary histories, using both existing species and the fossil record. Existing patterns of biodiversity have been shaped both by speciation and by extinction.[3]

Charles Darwin was the first to formulate a scientific argument for the theory of evolution by means of natural selection. Evolution by natural selection is a process inferred from three facts about populations: 1) more offspring are produced than can possibly survive, 2) traits vary among individuals, leading to different rates of survival and reproduction, and 3) trait differences are heritable.[4] Thus, when members of a population die they are replaced by the progeny of parents better adapted to survive and reproduce in the environment in which natural selection takes place. This process creates and preserves traits that are seemingly fitted for the functional roles they perform.[5] Natural selection is the only known cause of adaptation, but not the only known cause of evolution. Other, nonadaptive causes of evolution include mutation and genetic drift.[6]

In the early 20th century, genetics was integrated with Darwin's theory of evolution by natural selection through the discipline of population genetics. The importance of natural selection as a cause of evolution was accepted into other branches of biology. Moreover, previously held notions about evolution, such as orthogenesis and "progress" became obsolete.[7] Scientists continue to study various aspects of evolution by forming and testing hypotheses, constructing scientific theories, using observational data, and performing experiments in both the field and the laboratory. Biologists agree that descent with modification is one of the most reliably established facts in science.[8] Discoveries in evolutionary biology have made a significant impact not just within the traditional branches of biology, but also in other academic disciplines (e.g., anthropology and psychology) and on society at large.[9][10]

Contents

1 History of evolutionary thought
2 Heredity
3 Variation
3.1 Mutation
3.2 Sex and recombination
3.3 Gene flow
4 Mechanisms
4.1 Natural selection
4.2 Biased mutation
4.3 Genetic drift
4.4 Genetic hitchhiking
4.5 Gene flow
5 Outcomes
5.1 Adaptation
5.2 Co-evolution
5.3 Co-operation
5.4 Speciation
5.5 Extinction
6 Evolutionary history of life
6.1 Origin of life
6.2 Common descent
6.3 Evolution of life
7 Applications
8 Social and cultural responses
9 See also...
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