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Evolution

Evolution is the change in the heritable characteristics of biological populations over successive generations.[1][2] It occurs when evolutionary processes such as natural selection and genetic drift act on genetic variation, resulting in certain characteristics becoming more or less common within a population over successive generations.[3] The process of evolution has given rise to biodiversity at every level of biological organisation.[4][5]

This article is about evolution in biology. For related articles, see Outline of evolution. For other uses, see Evolution (disambiguation).

The scientific theory of evolution by natural selection was conceived independently by two British naturalists, Charles Darwin and Alfred Russel Wallace, in the mid-19th century as an explanation for why organisms are adapted to their physical and biological environments. The theory was first set out in detail in Darwin's book On the Origin of Species.[6] Evolution by natural selection is established by observable facts about living organisms: (1) more offspring are often produced than can possibly survive; (2) traits vary among individuals with respect to their morphology, physiology, and behaviour; (3) different traits confer different rates of survival and reproduction (differential fitness); and (4) traits can be passed from generation to generation (heritability of fitness).[7] In successive generations, members of a population are therefore more likely to be replaced by the offspring of parents with favourable characteristics for that environment.


In the early 20th century, competing ideas of evolution were refuted and evolution was combined with Mendelian inheritance and population genetics to give rise to modern evolutionary theory.[8] In this synthesis the basis for heredity is in DNA molecules that pass information from generation to generation. The processes that change DNA in a population include natural selection, genetic drift, mutation, and gene flow.[3]


All life on Earth—including humanity—shares a last universal common ancestor (LUCA),[9][10][11] which lived approximately 3.5–3.8 billion years ago.[12] The fossil record includes a progression from early biogenic graphite[13] to microbial mat fossils[14][15][16] to fossilised multicellular organisms. Existing patterns of biodiversity have been shaped by repeated formations of new species (speciation), changes within species (anagenesis), and loss of species (extinction) throughout the evolutionary history of life on Earth.[17] Morphological and biochemical traits tend to be more similar among species that share a more recent common ancestor, which historically was used to reconstruct phylogenetic trees, although direct comparison of genetic sequences is a more common method today.[18][19]


Evolutionary biologists have continued to study various aspects of evolution by forming and testing hypotheses as well as constructing theories based on evidence from the field or laboratory and on data generated by the methods of mathematical and theoretical biology. Their discoveries have influenced not just the development of biology but also other fields including agriculture, medicine, and computer science.[20]

Variation exists within populations of organisms with respect to morphology, physiology and behaviour (phenotypic variation).

Different traits confer different rates of survival and reproduction (differential fitness).

These traits can be passed from generation to generation (heritability of fitness).

 – Notion that species can revert to primitive forms

Devolution (biology)

on In Our Time at the BBC

"Evolution"

. Washington, DC: National Academy of Sciences. Retrieved 30 May 2011.

"Evolution Resources from the National Academies"

. Berkeley, California: University of California, Berkeley. Retrieved 30 May 2011.

"Understanding Evolution: your one-stop resource for information on evolution"

. Arlington County, Virginia: National Science Foundation. Archived from the original on 19 May 2011. Retrieved 30 May 2011.

"Evolution of Evolution – 150 Years of Darwin's 'On the Origin of Species'"

. Smithsonian Institution, National Museum of Natural History. 28 January 2010. Retrieved 14 July 2018. Adobe Flash required.

"Human Evolution Timeline Interactive"

"". Salon. Retrieved 2021-08-24.

History of Evolution in the United States

on YouTube

Video (1980; Cosmos animation; 8:01): "Evolution" – Carl Sagan