Concept

Natural selection

Overview

Natural selection is the differential survival and reproduction of individuals due to differences in the relative fitness endowed on them by their own particular complement of observable characteristics. It is a key law or mechanism of evolution which changes the heritable traits characteristic of a population or species over generations. Charles Darwin popularised the term "natural selection", contrasting it with artificial selection, which is intentional, whereas natural selection is not.

For Darwin, natural selection was a law or principle which resulted from three different kinds of process: inheritance, including the transmission of heritable material from parent to offspring and its development (ontogeny) in the offspring; variation, which partly resulted from an organism's own agency; and the struggle for existence, which included both competition between organisms and cooperation or 'mutual aid' (particularly in 'social' plants and social animals).

Variation of traits, both genotypic and phenotypic, exists within all populations of organisms. However, some traits are more likely to facilitate survival and reproductive success. Thus, these traits are more likely to be passed on to the next generation. These traits can also become more common within a population if the environment that favours these traits remains fixed. If new traits become more favoured due to changes in a specific niche, microevolution occurs. If new traits become more favoured due to changes in the broader environment, macroevolution occurs. Sometimes, new species can arise especially if these new traits are radically different from the traits possessed by their predecessors.

The likelihood of these traits being 'selected' and passed down is determined by many factors. Some are likely to be passed down because they adapt well to their environments. Others are passed down because these traits are actively preferred by mating partners, which is known as sexual selection. Female bodies also prefer traits that confer the lowest cost to their reproductive health, which is known as fecundity selection.

Natural selection is a cornerstone of modern biology. The concept, published by Darwin and Alfred Russel Wallace in a joint presentation of papers in 1858, was elaborated in Darwin's influential 1859 book On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life. He described natural selection as analogous to artificial selection, a process by which animals and plants with traits considered desirable by human breeders are systematically favoured for reproduction. The concept of natural selection originally developed in the absence of a valid theory of heredity; at the time of Darwin's writing, science had yet to develop modern theories of genetics. The union of traditional Darwinian evolution with subsequent discoveries in classical genetics formed the modern synthesis of the mid-20th century.

New evidence has prompted 21st century evolutionary biologists to challenge the 20th century's gene-centred view of evolution, producing several extended evolutionary syntheses which bring organisms back to the heart of the theory of natural selection. Convergently, the growth of molecular genetics has led to evolutionary developmental biology, which compares the developmental processes of different organisms to infer how developmental processes evolved. While it is now recognised that genotypes can slowly change by random genetic drift, natural selection remains the primary explanation for adaptive evolution.

Overview adapted from Wikipedia (CC BY-SA 4.0; see the article history for authors).

In the original texts

Passages from public-domain books where Natural selection is discussed.

Several writers have misapprehended or objected to the term Natural Selection. Some have even imagined that natural selection induces variability, whereas it implies only the preservation of such variations as arise and are beneficial to the being under its conditions of life. No one objects to agriculturists speaking of the potent effects of man’s selection; and in this case the individual differences given by…
Charles Darwin, The Origin of Species by Means of Natural Selection
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On the other hand, we may feel sure that any variation in the least degree injurious would be rigidly destroyed. This preservation of favourable variations and the rejection of injurious variations, I call Natural Selection. Variations neither useful nor injurious would not be affected by natural selection, and would be left a fluctuating element, as perhaps we see in the species called polymorphic.
Charles Darwin, On the Origin of Species By Means of Natural Selection
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"But if natural selection is a mere phrase, vague enough and wide enough to cover any number of the physical causes concerned in ordinary generation, then the whole of Mr. Spencer's laborious argument in favour of his 'other factor' becomes an argument worse than superfluous. It is wholly fallacious in assuming that this 'factor' and 'natural selection' are at all exclusive of, or even separate from, each other. The…
Herbert Spencer, Essays
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Only in cases of variations which are specially preservative, as for example, great cunning during a relatively barbarous state, can we expect increase from natural selection alone. We cannot suppose that minor traits, exemplified among others by the æsthetic perceptions, can have been evolved by natural selection. But if there is inheritance of functionally-produced modifications of structure, evolution of such…
Herbert Spencer, The Factors of Organic Evolution
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But even this is not altogether correct, for he ventures to say of the varying species, "The part played by descent is on the contrary a very secondary activity of nature." There is heredity, then, but it is only to be reckoned as a factor of the second class. Let us be glad that heredity of which Herr Duehring has said so much that is evil and mysterious is at least let in by the back door. It is just the same with…
Friedrich Engels, Landmarks of Scientific Socialism
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Philosophers who discussed Natural selection

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Zoology

Place in the tradition

Part of Aesthetics.

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