Natural selection is a process by which biological populations are altered over time, as a result of the propagation of heritable traits that affect the capacity of individual organisms to survive and reproduce. It is one of several mechanisms that give rise to the evolution of biological species (other mechanisms include genetic drift and gene flow.) However, natural selection has a special significance because it is believed to be the one responsible for organisms being adapted to their environment. The theory of natural selection was proposed by Charles Darwin and Alfred Russel Wallace in 1858, though vaguer and more obscure formulations had been arrived at by earlier workers. Main article: Life There are many universal units and common processes that are fundamental to the known forms of life. ... Heritability, as used professionally in genetics, has a very precise definition. ... In biology and ecology, an organism (in Greek organon = instrument) is an assembly of molecules that influence each other in such a way that they function as a more or less stable whole and have properties of life. ... Reproduction is perhaps most commonly used in the context of biological reproduction and sex: Sexual reproduction is a biological process by which organisms create descendants through the combination of genetic material. ... Charles Darwin, father of the theory of evolution by natural selection. ... In biology, a species is a kind of organism. ... Genetic drift is a mechanism of evolution that acts in concert with natural selection to change the characteristics of species over time. ... Gene flow (also known as gene migration) is the transfer of genes from one population to another. ... A biological adaptation is an anatomical structure, physiological process or behavioral trait of an organism that has evolved over a period of time by the process of natural selection such that it increases the expected long-term reproductive success of the organism. ... Charles Darwin, about the same time as the publication of The Origin of Species. ... Alfred Russel Wallace Alfred Russel Wallace (January 8, 1823 — November 7, 1913) was a British naturalist, geographer, anthropologist and biologist. ... 1858 is a common year starting on Friday. ...

Natural selection can be subdivided into two types: (i) ecological selection, which arises from the portion of an organism's environment not related to direct sexual competition (such as the availability of food, the presence of predators, and so forth); and (ii) sexual selection, which arises from the competition for mates between individuals of the same sex. The reason for this division is that the effects of sexual selection can produce results that seem counter-intuitive from the point of view of ecological selection alone (a famous example being the tails of peacocks, which, though cumbersome, serve an important purpose in courtship displays.) Ecological selection (or environmental selection or survival selection or individual selection or asexual selection) refers to natural selection minus sexual selection, i. ... Look up Sex in Wiktionary, the free dictionary The members of many species of living things are divided into two or more categories called sexes (or loosely speaking, genders). ... This snapping turtle is trying to make a meal of a Canada goose, but the goose is too wary. ... Illustration from The Descent of Man and Selection in Relation to Sex by Charles Darwin showing the tufted coquette Lophornis ornatus, female on left, ornamented male on right. ... Peacock re-directs here; for alternate uses see Peacock (disambiguation). ... Dates romantically sharing a chili cheese dog, in a dream sequence Courtship (sometimes called dating or going steady) is the process of selecting and attracting a mate for marriage. ...

Natural selection is distinguished from artificial selection, which is the alteration of domesticated species resulting from human intervention as opposed the "natural environment". However, the mechanisms of natural and artifical selection are essentially identical, and in fact the observed effects of artifical selection were used by Darwin to illustrate how natural selection works. ... Domesticated animals, plants, and other organisms are those whose collective behavior, life cycle, or physiology has been altered as a result of their breeding and living conditions being under human control for multiple generations. ... Binomial name Homo sapiens Linnaeus, 1758 Subspecies Homo sapiens idaltu (extinct) Homo sapiens sapiens Human beings define themselves in biological, social, and spiritual terms. ...

The modern theory of natural selection is formulated in terms of genetic differences between individuals, resulting in differences in the frequency of alleles in a population over successive generations. The genetic variation on which natural selection acts are now understood to arise from random mutations. Genetics (from the Greek genno γεννώ= give birth) is the science of genes, heredity, and the variation of organisms. ... An allele is any one of a number of alternative forms of the same gene occupying a given locus (position) on a chromosome. ... The gene pool of a species or a population is the complete set of unique alleles that would be found by inspecting the genetic material of every living member of that species or population. ... Mutations are permanent, sometimes transmissible (if the change is to a germ cell) changes to the genetic material (usually DNA or RNA) of a cell. ...

Overview

The basic concept of natural selection is that conditions (or "nature") determine (or "select") how well particular traits of organisms can serve the survival and reproduction of the organism; organisms lacking these traits might die before reproducing, or be less prolific. As long as environmental conditions remain the same, or similar enough that these traits continue to be adaptive, such traits will become more common within populations. Loss of the species' ecological niche or crowding-out due to population growth can change drastically the adaptive traits required to survive - in such conditions, or in any circumstance where survival is determined by ecology more than by the secondary sexual characteristics, an ecological selection is taking place (this term is used solely to differentiate processes irrelevant to mating, and is of modern usage, having grown up with the field of ecology itself). In ecology, a niche is a term describing the relational position of a species or population in an ecosystem. ... Population growth is changing of the amount of population over time. ... Ecological selection (or environmental selection or survival selection or individual selection or asexual selection) refers to natural selection minus sexual selection, i. ... Ecology is sometimes used as an incorrect synonym for the natural environment. ...

Darwin's scientific theory of the evolution of species through natural selection starts from the premise that an organism's traits vary in a non-deterministic way from parent to offspring, a process called "individuation" by Darwin. This theory does not make any specific claims as to how this process works, although more recent scientific discoveries in genetics explain several mechanisms that occur in the process of reproduction: in the case of both asexual and sexual reproduction, random mutation (including DNA transcription errors); in the case of sexual reproduction (which mixes the DNA of two parents into an offspring), gene flow and genetic drift are also important mechanisms. Competition (typically among males to impregnate females) for mates produces sexual selection - a process which Darwin considered secondary to ecological in most species. Charles Darwin, father of the theory of evolution by natural selection. ... In biology, a species is a kind of organism. ... This article is about the general notion of determinism in philosophy. ... Genetics (from the Greek genno γεννώ= give birth) is the science of genes, heredity, and the variation of organisms. ... Space-filling model of a section of DNA molecule Deoxyribonucleic acid (DNA) or deoxyribose nucleic acid is a nucleic acid that contains the genetic instructions specifying the biological development of all cellular forms of life (and many viruses). ... Transcription may be one of the following: In linguistics, transcription is the conversion of spoken words into written language. ... Gene flow (also known as gene migration) is the transfer of genes from one population to another. ... Genetic drift is a mechanism of evolution that acts in concert with natural selection to change the characteristics of species over time. ... Illustration from The Descent of Man and Selection in Relation to Sex by Charles Darwin showing the tufted coquette Lophornis ornatus, female on left, ornamented male on right. ...

Natural selection does not distinguish between ecological selection and sexual selection, as it is concerned with traits, e.g. dexterity of movement, on which both may operate simultaneously. If a particular variation makes the offspring which manifest it better suited to survival or to successful reproduction, that offspring and its descendants will be more likely to survive than those offspring without the variation. The original traits, as well as any maladaptive variations, will disappear as the offspring who carry them are replaced by their more successful relatives. Ecological selection (or environmental selection or survival selection or individual selection or asexual selection) refers to natural selection minus sexual selection, i. ... Illustration from The Descent of Man and Selection in Relation to Sex by Charles Darwin showing the tufted coquette Lophornis ornatus, female on left, ornamented male on right. ...

Therefore, certain traits are preserved due to the selective advantage they provide to their holders, allowing the individual to leave more offspring than individuals without the trait(s). Eventually, through many iterations of this process, organisms will develop more and more complex adaptive traits.

Mechanisms of natural selection

In Chapter 4 of the the The Origin of Species, Darwin wrote:

It may be said that natural selection is daily and hourly scrutinising, throughout the world, every variation, even the slightest; rejecting that which is bad, preserving and adding up all that is good; silently and insensibly working, whenever and wherever opportunity offers, at the improvement of each organic being in relation to its organic and inorganic conditions of life. We see nothing of these slow changes in progress, until the hand of time has marked the long lapses of ages, and then so imperfect is our view into long past geological ages, that we only see that the forms of life are now different from what they formerly were.

What makes one trait more likely to succeed is highly dependent on environmental factors, including the species' predators, food sources, abiotic stress, physical environment, and so on. When members of a species become separated, such as geographically, they face different environments, and tend to develop in different directions. After a long period of time, their traits will have developed along different paths to such an extent that they can no longer interbreed, at which point they are considered separate species. This is why a species will sometimes separate into multiple species, rather than simply being replaced by a newer form of the species (from this fact Darwin suggested that all species today have evolved from a common ancestor). Abiotic stress is caused in living organisms by nonliving environmental factors, such as drought, extreme temperatures, soil conditions, and high winds. ...

Additionally, some scientists have theorized that an adaptation which serves to make the organism more adaptable in the future will also tend to supplant its competitors even though it provides no specific advantage in the near term. Descendants of that organism will be more varied and therefore more resistant to extinction due to environmental catastrophes and extinction events. This has been proposed as one reason for the rise of mammals. While this form of selection is possible, it is more likely to play an important role in cases where selection for adaptation is continuous. For example, the Red Queen hypothesis suggests that sex might have evolved to help organisms adapt to deal with parasites. An extinction event (also extinction-level event, ELE) is a period in time when a large number of species die out. ... Orders Subclass Monotremata Monotremata Subclass Marsupialia Didelphimorphia Paucituberculata Microbiotheria Dasyuromorphia Peramelemorphia Notoryctemorphia Diprotodontia Subclass Placentalia Xenarthra Dermoptera Desmostylia Scandentia Primates Rodentia Lagomorpha Insectivora Chiroptera Pholidota Carnivora Perissodactyla Artiodactyla Cetacea Afrosoricida Macroscelidea Tubulidentata Hyracoidea Proboscidea Sirenia The mammals are the class of vertebrate animals primarily characterized by the presence of mammary... The Red Queen or Red Queens Race is an evolutionary theory explaining the advantage of sex. ... Look up Sex in Wiktionary, the free dictionary The members of many species of living things are divided into two or more categories called sexes (or loosely speaking, genders). ...

Natural selection can be expressed as the following general law (taken from the conclusion of The Origin of Species): The 1859 edition of On the Origin of Species First published in 1859, The Origin of Species (full title On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life) by British naturalist Charles Darwin is one of the pivotal...

1. IF there are organisms that reproduce, and
2. IF offspring inherit traits from their progenitor(s), and
3. IF there is variability of traits, and
4. IF the environment cannot support all members of a growing population,
5. THEN those members of the population with less-adaptive traits (determined by the environment) will die out, and
6. THEN those members with more-adaptive traits (determined by the environment) will thrive

The result is the evolution of species. In biology, a species is a kind of organism. ...

This is a continuing process—it accounts for how species change, and can account for both the extinction of one species and the creation of a new one. The formulation does not rule out selection occurring at all biological levels (e.g. gene, organism, group), and the particular process of introducing new traits does not matter.

Darwin did not maintain that natural selection was the only mechanism of evolution, however, as he pronounced in the introduction to the The Origin of Species: "I am convinced that [it] has been the most important, but not the exclusive means of modification."

History of the principle

Charles Darwin's discovery of the principle of natural selection, as his explanation for the origin of species, occurred in about 1838. Over the next twenty years, he shared it with only a very small number of acquaintances, while he amassed evidence in its favor. He first outlined his theory in two unpublished manuscripts, written in 1842 and 1844. In 1858, Alfred Russel Wallace independently discovered the principle, and wrote a letter to Darwin, explaining his hypothesis. This prompted a reading, at the Linnean Society, of tracts from both men describing the principle that year. Darwin published his detailed theory the following year, in The Origin of Species. The Linnean Society of London is the worlds premier society for the study and dissemination about taxonomy. ... The 1859 edition of On the Origin of Species First published in 1859, The Origin of Species (full title On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life) by British naturalist Charles Darwin is one of the pivotal...

Unbeknownst to both Darwin and Wallace, the principle of natural selection had been previously hypothesized by others. Pierre Louis Moreau de Maupertuis in 1745, Erasmus Darwin in 1794-1796, William Charles Wells in 1813, and Patrick Matthew in 1831 were amongst the first to grasp the idea. Maupertuis' discovery is in dispute, but has enough substantial evidence in its favor to warrant mention. Erasmus Darwin was a contemporary and colleague of Wells — not to mention the grandfather of Charles Darwin — and he expressed much of his theory of evolution in poetic verse. His formal exposition of the hypothesis lacks a structured formulation, but has enough merit to be considered a possibility. Wells' hypothesis, applied solely to explain the origin of human races, had been presented in person at the Royal Society. Matthew's hypothesis had appeared in an appendix to his book on arboriculture. Richard Owen also claimed precedence over Darwin. Edward Blyth had also proposed natural selection, as a mechanism of keeping species constant. Pierre Louis Maupertuis, here wearing lapmudes or a fur coat from his Lapland expedition. ... Erasmus Darwin Stone-cast bust of Erasmus Darwin, by William John Coffee, c 1795, (Crown Derby Modeller and world renown artist) Erasmus Darwin (December 12, 1731 – April 18, 1802) trained as a physician and wrote extensively on medicine and botany, as well as poetry. ... William Charles Wells (1757 — 1817) was Wells was born Charlestown, where? and was sent to school in Dumfries and later attended the University of Edinburgh. ... 1813 is a common year starting on Friday (link will take you to calendar). ... Patrick Matthew Patrick Matthew (20 October 1790 — 8 June 1874) was a Scottish fruit grower who had proposed the principle of natural selection as a mechanism of evolution over a quarter-century earlier than did Charles Darwin and Alfred Russel Wallace. ... 1831 was a common year starting on Saturday (see link for calendar). ... The Royal Society of London for the Improvement of Natural Knowledge, known simply as the Royal Society, is claimed to be the oldest learned society still in existence. ... Arboriculture is the selection, planting and care of individual trees, shrubs, vines, and other woody perennial plants, and the study of how they grow and respond to cultural practices and the environment. ... Sir Richard Owen and Dinornis bird skeleton Sir Richard Owen (July 20, 1804 - December 18, 1892) was an English biologist, comparative anatomist and palaeontologist. ... Edward Blyth (December 23, 1810 - December 27, 1873) was an English zoologist. ...

Scope and role of natural selection

Natural selection need not apply solely to biological organisms; in theory, it applies to all systems in which entities reproduce in a way that includes both inheritance and variation. Thus, a form of natural selection can occur in the non-biological realm. Computer-based systems have shown that natural selection can be be highly effective in adapting entities to their environments. However, Stephen Wolfram, who has extensively studied such systems, has concluded that they also have shown that natural selection per se does not originate complexity, something that is often attributed to it: Stephen Wolfram (born August 29, 1959 in London) is a scientist known for his work in particle physics, cellular automata and computer algebra, and is the author of the computer program Mathematica. ...

My own work on cellular automata in the early 1980s showed that great complexity could be generated just from simple programs, without any process like natural selection. But although I and others believed that my results should be relevant to biological systems there was still a pervasive belief that the level of complexity seen in biology must somehow be uniquely associated with natural selection. In the late 1980s the study of artificial life caused several detailed computer simulations of natural selection to be done, and these simulations reproduced various known features of biological evolution. But from looking at such simulations, as well as from my own experiments done from 1980 onwards, I increasingly came to believe that almost any complexity being generated had its origin in phenomena similar to those I had seen in cellular automata—and had essentially nothing to do with natural selection. (Wolfram, p. 1001)

A cellular automaton (plural: cellular automata) is a discrete model studied in computability theory and mathematics. ... There are different senses of complexity: In information processing, complexity is a measure of the total number of properties transmitted by an object and detected by an observer. ... Artificial life, also known as alife or a-life, is the study of life through the use of human-made analogs of living systems. ...

Impact of the idea

Perhaps the most radical claim of Darwin's theory of evolution through natural selection is that "elaborately constructed forms, so different from each other, and dependent on each other in so complex a manner" have evolved out of the simplest forms of life and according to a few simple principles. It is this fundamental claim that has inspired some of Darwin's most ardent supporters--and that has provoked the most profound opposition.

In addition, many theories of Artificial selection have been proposed to suggest that economic or social fitness factors assessed by other humans or their built environments are somehow biological or inevitable - Social Darwinism. Others held that there was an evolution of societies analogous to that of species. Many theories of eugenics were created in an attempt to address these issues. Darwin's ideas, along with those of Adam Smith and Karl Marx, are considered by most historians to have had a profound influence on 19th century thought, and to have challenged the standing rationalist and religious fundamentalist schools of thought that prevailed in Europe. ... Social Darwinism is a social theory which holds that Darwins theory of evolution by natural selection affects not only the distribution of biological traits in a population, but that it affects human social institutions as well. ... Cultural evolution is the structural development (change) of a society over time. ... Eugenics is the self-direction of human evolution: Logo from the Second International Congress of Eugenics, 1921, depicting it as a tree which unites a variety of different fields. ... Adam Smith Adam Smith (Baptised June 5, 1723 – July 17, 1790) was a Scottish political economist and moral philosopher. ... Karl Marx Karl Heinrich Marx (May 5, 1818 Trier, Germany – March 14, 1883 London, UK) was an influential German philosopher, political economist, and revolutionary organizer of the International Workingmens Association, whose two books, Das Kapital and The Communist Manifesto (the latter with Friedrich Engels), laid the foundations of Marxism... Alternative meaning: Nineteenth Century (periodical) (18th century — 19th century — 20th century — more centuries) As a means of recording the passage of time, the 19th century was that century which lasted from 1801-1900 in the sense of the Gregorian calendar. ... This article is not about continental rationalism. ... Fundamentalism is a movement to maintain strict adherence to founding principles. ... A satellite composite image of Europe Europe is geologically and geographically a peninsula, forming the westernmost part of Eurasia. ...

References

• Darwin, Charles (1859). The Origin of Species (First Edition).
• Wolfram, Stephen (2002), A New Kind of Science. Wolfram Media, Inc. ISBN 1579550088

A New Kind of Science is a controversial book by Stephen Wolfram, published in 2002. ...

External links

• Introduction to evolutionary biology (has a section on natural selection in context of evolution)
• Evolution by Natural Selection - An introduction to the logic of the theory of natural selection
• Darwin's Precursors and Influences. Part 4 -- Natural selection; by John Wilkins

See also

• artificial selection
• directional selection
• disruptive selection
• ecological selection
• evolution
• Fitness
• genetic drift
• negative selection
• selection
• sexual selection
• stabilizing selection
• survival of the fittest