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Natural selection

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General principlesEdit

File:Darwin's finches.jpeg





Nomenclature and usageEdit


Following Darwin's primary usage[1] the term is often used to refer to both the evolutionary consequence of blind selection and to its mechanisms.[2][3] It is sometimes helpful to explicitly distinguish between selection's mechanisms and its effects; when this distinction is important, scientists define "natural selection" specifically as "those mechanisms that contribute to the selection of individuals that reproduce", without regard to whether the basis of the selection is heritable. This is sometimes referred to as "phenotypic natural selection".[4]



Main article: Fitness (biology)

The concept of fitness is central to natural selection. Broadly, individuals which are more "fit" have better potential for survival, as in the well-known phrase "survival of the fittest". However, as with natural selection above, the precise meaning of the term is much more subtle, and Richard Dawkins manages in his later books to avoid it entirely. (He devotes a chapter of his book, The Extended Phenotype, to discussing the various senses in which the term is used). Modern evolutionary theory defines fitness not by how long an organism lives, but by how successful it is at reproducing. If an organism lives half as long as others of its species, but has twice as many offspring surviving to adulthood, its genes will become more common in the adult population of the next generation.



Types of selectionEdit



File:Life cycle of a sexually reproducing organism.svg


The fecundity of both females and males (for example, giant sperm in certain species of Drosophila)[7] can be limited via "fecundity selection". The viability of produced gametes can differ, while intragenomic conflicts such as meiotic drive between the haploid gametes can result in gametic or "genic selection". Finally, the union of some combinations of eggs and sperm might be more compatible than others; this is termed compatibility selection.

Sexual selectionEdit

Main article: Sexual selection




Examples of natural selectionEdit

File:Antibiotic resistance.svg




The widespread use and misuse of antibiotics has resulted in increased microbial resistance to antibiotics in clinical use, to the point that the methicillin-resistant Staphylococcus aureus (MRSA) has been described as a "superbug" because of the threat it poses to health and its relative invulnerability to existing drugs.[11] Response strategies typically include the use of different, stronger antibiotics; however, new strains of MRSA have recently emerged that are resistant even to these drugs.[12]


Evolution by means of natural selectionEdit

Main article: Evolution


File:Pavo cristatus albino001xx.jpg


Some mutations occur in so-called regulatory genes. Changes in these can have large effects on the phenotype of the individual because they regulate the function of many other genes. Most, but not all, mutations in regulatory genes result in non-viable zygotes. Examples of nonlethal regulatory mutations occur in HOX genes in humans, which can result in a cervical rib[17] or polydactyly, an increase in the number of fingers or toes.[18] When such mutations result in a higher fitness, natural selection will favor these phenotypes and the novel trait will spread in the population.

File:Polydactyly 01 Lhand AP.jpg



Main article: Speciation



Historical developmentEdit

Main article: History of evolutionary thought
Charles Darwin aged 51


Pre-Darwinian theoriesEdit

Several ancient philosophers expressed the idea that nature produces a huge variety of creatures, apparently randomly, and that only those creatures survive that manage to provide for themselves and reproduce successfully; well-known examples include Empedocles[21] and his intellectual successor, Lucretius,[22] while related ideas were later refined by Aristotle.[23] The struggle for existence was later described by al-Jahiz in the 9th century.[24][25] Such classical arguments were reintroduced in the 18th century by Pierre Louis Maupertuis[26] and others, including Charles Darwin's grandfather Erasmus Darwin. While these forerunners had an influence on Darwinism, they later had little influence on the trajectory of evolutionary thought after Charles Darwin.

Until the early 19th century, the prevailing view in Western societies was that differences between individuals of a species were uninteresting departures from their Platonic idealism (or typus) of created kinds. However, the theory of uniformitarianism in geology promoted the idea that simple, weak forces could act continuously over long periods of time to produce radical changes in the Earth's landscape. The success of this theory raised awareness of the vast scale of geological time and made plausible the idea that tiny, virtually imperceptible changes in successive generations could produce consequences on the scale of differences between species. Early 19th century evolutionists such as Jean Baptiste Lamarck suggested the inheritance of acquired characteristics as a mechanism for evolutionary change; adaptive traits acquired by an organism during its lifetime could be inherited by that organism's progeny, eventually causing transmutation of species.[27] This theory has come to be known as Lamarckism and was an influence on the anti-genetic ideas of the Stalinist Soviet biologist Trofim Lysenko.[28]

Darwin's theoryEdit




Darwin thought of natural selection by analogy to how farmers select crops or livestock for breeding, which he called "artificial selection"; in his early manuscripts he referred to a 'Nature' which would do the selection. At the time, other mechanisms of evolution such as evolution by genetic drift were not yet explicitly formulated, and Darwin believed that selection was likely only part of the story: "I am convinced that [it] has been the main, but not exclusive means of modification."[36] In a letter to Charles Lyell in September 1860, Darwin regretted the use of the term "Natural Selection", preferring the term "Natural Preservation".[37] For Darwin and his contemporaries, natural selection was essentially synonymous with evolution by natural selection. After the publication of The Origin of Species, educated people generally accepted that evolution had occurred in some form. However, natural selection remained controversial as a mechanism, partly because it was perceived to be too weak to explain the range of observed characteristics of living organisms, and partly because even supporters of evolution balked at its "unguided" and non-progressive nature,[38] a response that has been characterized as the single most significant impediment to the idea's acceptance.[39] However, some thinkers enthusiastically embraced natural selection; after reading Darwin, Herbert Spencer introduced the term survival of the fittest, which became a popular summary of the theory.[40] The fifth edition of On the Origin of Species published in 1869 included Spencer's phrase as an alternative to natural selection, with credit given: "But the expression often used by Mr. Herbert Spencer, of the Survival of the Fittest, is more accurate, and is sometimes equally convenient."[41] Although the phrase is still often used by non-biologists, modern biologists avoid it because it is tautological if "fittest" is read to mean "functionally superior" and is applied to individuals rather than considered as an averaged quantity over populations.[42]

Modern evolutionary synthesisEdit

Main article: Modern evolutionary synthesis

Natural selection relies crucially on the idea of heredity, but it was developed long before the basic concepts of genetics. Although Austrian monk Gregor Mendel, the father of modern genetics, was a contemporary of Darwin's, his work would lie in obscurity until the early 20th century. Only after the integration of Darwin's theory of evolution with a complex statistical appreciation of Gregor Mendel's 're-discovered' laws of inheritance did natural selection become generally accepted by scientists. The work of Ronald Fisher (who developed the required mathematical language and the genetical theory of natural selection),[2] J.B.S. Haldane (who introduced the concept of the "cost" of natural selection),[43] Sewall Wright (who elucidated the nature of selection and adaptation),[44] Theodosius Dobzhansky (who established the idea that mutation, by creating genetic diversity, supplied the raw material for natural selection: see Genetics and the Origin of Species),[45] William Hamilton (who conceived of kin selection), Ernst Mayr (who recognised the key importance of reproductive isolation for speciation: see Systematics and the Origin of Species)[46] and many others formed the modern evolutionary synthesis. This synthesis cemented natural selection as the foundation of evolutionary theory, where it remains today.

Impact of the ideaEdit


Social and psychological theoryEdit


More recently, work among anthropologists and psychologists has led to the development of sociobiology and later evolutionary psychology, a field that attempts to explain features of human psychology in terms of adaptation to the ancestral environment. The most prominent such example, notably advanced in the early work of Noam Chomsky and later by Steven Pinker, is the hypothesis that the human brain is adapted to acquire the grammatical rules of natural language.[51] Other aspects of human behavior and social structures, from specific cultural norms such as incest avoidance to broader patterns such as gender roles, have been hypothesized to have similar origins as adaptations to the early environment in which modern humans evolved. By analogy to the action of natural selection on genes, the concept of memes - "units of cultural transmission", or culture's equivalents of genes undergoing selection and recombination - has arisen, first described in this form by Richard Dawkins[52] and subsequently expanded upon by philosophers such as Daniel Dennett as explanations for complex cultural activities, including human consciousness.[53] Extensions of the theory of natural selection to such a wide range of cultural phenomena have been distinctly controversial and are not widely accepted.[54]

Information and systems theoryEdit

In 1922, Alfred Lotka proposed that natural selection might be understood as a physical principle which could be described in terms of the use of energy by a system,[55] a concept that was later developed by Howard Odum as the maximum power principle whereby evolutionary systems with selective advantage maximise the rate of useful energy transformation. Such concepts are sometimes relevant in the study of applied thermodynamics.

The principles of natural selection have inspired a variety of computational techniques, such as "soft" artificial life, that simulate selective processes and can be highly efficient in 'adapting' entities to an environment defined by a specified fitness function.[56] For example, a class of heuristic optimization algorithms known as genetic algorithms, pioneered by John Holland in the 1970s and expanded upon by David E. Goldberg,[57] identify optimal solutions by simulated reproduction and mutation of a population of solutions defined by an initial probability distribution.[58] Such algorithms are particularly useful when applied to problems whose solution landscape is very rough or has many local minima.

Genetic basis of natural selectionEdit


Genotype and PhenotypeEdit

See also: Genotype-phenotype distinction.




Directionality of selectionEdit





Selection and genetic variationEdit


Mutation selection balanceEdit


Genetic linkageEdit





See alsoEdit


  2. 2.0 2.1 Fisher RA (1930) The Genetical Theory of Natural Selection Clarendon Press, Oxford
  3. Works employing or describing this usage:
    Endler JA (1986). Natural Selection in the Wild, Princeton, New Jersey: Princeton University Press.
    Williams GC (1966). Adaptation and Natural Selection, Oxford University Press.
  4. Works employing or describing this usage:
  6. Modified from Christiansen FB (1984) The definition and measurement of fitness. In: Evolutionary ecology (ed. Shorrocks B) pp65-79. Blackwell Scientific, Oxford by adding survival selection in the reproductive phase
  8. Andersson, M (1995). Sexual Selection, Princeton, New Jersey: Princeton University Press.
  9. Eens M, Pinxten R. (2000). Sex-role reversal in vertebrates: behavioural and endocrinological accounts. Behav Processes 51(1-3):135-147. PMID 11074317
  11. MRSA Superbug News. URL accessed on 2006-05-06.
  12. Schito GC (2006). The importance of the development of antibiotic resistance in Staphylococcus aureus. Clin Microbiol Infect 12 Suppl 1: 3–8. [1]
  13. Lucy A, Guo H, Li W, Ding S (2000). "Suppression of post-transcriptional gene silencing by a plant viral protein localized in the nucleus". EMBO J 19 (7): 1672–80. PMID 10747034.
  14. Kryukov GV, Schmidt S & Sunyaev S (2005) Small fitness effect of mutations in highly conserved non-coding regions. Human Molecular Genetics 14:2221-9
  16. Eyre-Walker A, Woolfit M, Phelps T. (2006). The distribution of fitness effects of new deleterious amino acid mutations in humans. Genetics 173(2):891-900. PMID 16547091
  17. Galis F (1999) Why do almost all mammals have seven cervical vertebrae? developmental constraints, Hox genes, and cancer. J Exp Zool 285:19-26
  19. Sanyal S, Jansen HG, de Grip WJ, Nevo E, de Jong WW. (1990). The eye of the blind mole rat, Spalax ehrenbergi. Rudiment with hidden function? Invest Ophthalmol Vis Sci. 1990 31(7):1398-404. PMID 2142147
  20. Salzburger W, Baric S, Sturmbauer C. (2002). Speciation via introgressive hybridization in East African cichlids? Mol Ecol 11(3): 619–625. PMID 11918795
  21. Empedocles, On Nature, Book II 
  22. Lucretius, De rerum natura, Book V 
  23. Aristotle, Physics, Book II, Chapters 4 and 8 
  26. Maupertuis, Pierre Louis (1748). Derivation of the laws of motion and equilibrium from a metaphysical principle (Original French text). Histoire de l'academie des sciences et belle lettres de Berlin 1746: 267–294.
  27. Chevalier de Lamarck J-B, de Monet PA (1809) Philosophie Zoologique
  28. Joravsky D. (1959). Soviet Marxism and Biology before Lysenko. Journal of the History of Ideas 20(1):85-104.
  29. Darwin 1859, p. 61
  30. Darwin 1859, p. 5
  31. T. Robert Malthus. An Essay on the Principle of Population. June 29, 1999. URL accessed on 2008-11-03.
  32. Orrell, David (2007) Apollo's Arrow Toronto: HarperCollins Publishers Ltd. [2]
  33. Charles Darwin, ed. Nora Barlow. The autobiography of Charles Darwin 1809-1882. London: Collins. URL accessed on 2008-11-03.
  34. Wallace, Alfred Russel (1870) Contributions to the Theory of Natural Selection New York: Macmillan & Co. [3]
  35. Darwin 1861, p. xiii
  36. Darwin 1859, p. 6
  37. Darwin Correspondence Online Database: Darwin, C. R. to Lyell, Charles, 28 September 1860. URL accessed on 2006-05-10.
  39. Kuhn TS. [1962] (1996). The Structure of Scientific Revolution 3rd ed. University of Chicago Press: Chicago, Illinois, USA. ISBN 0-226-45808-3
  40. Pioneers of Psychology [2001 Tour - School of Education & Psychology]. URL accessed on 2007-08-29.
     Maurice E. Stucke. Better Competition Advocacy. URL accessed on 2007-08-29.
  41. Darwin 1872, p. 49.
  42. Mills SK, Beatty JH. [1979] (1994). The Propensity Interpretation of Fitness. Originally in Philosophy of Science (1979) 46: 263-286; republished in Conceptual Issues in Evolutionary Biology 2nd ed. Elliott Sober, ed. MIT Press: Cambridge, Massachusetts, USA. pp3-23. ISBN 0-262-69162-0.
  43. Haldane JBS (1932) The Causes of Evolution; Haldane JBS (1957) The cost of natural selection. J Genet 55:511-24([4].
  44. Wright S (1932) The roles of mutation, inbreeding, crossbreeding and selection in evolution Proc 6th Int Cong Genet 1:356–66
  45. Dobzhansky Th (1937) Genetics and the Origin of Species Columbia University Press, New York. (2nd ed., 1941; 3rd edn., 1951)
  46. Mayr E (1942) Systematics and the Origin of Species Columbia University Press, New York. ISBN 0-674-86250-3
  47. The New York Review of Books: Darwinian Fundamentalism (accessed May 6, 2006)
  48. Engels F (1873-86) Dialectics of Nature 3d ed. Moscow: Progress, 1964 [5]
  49. Quoted in translation in Eisenberg L (2005) Which image for Lorenz? Am J Psychiatry 162:1760 [6]
  50. e.g. Wilson, DS (2002) Darwin's Cathedral: Evolution, Religion, and the Nature of Society. University of Chicago Press, ISBN 0-226-90134-3
  51. Pinker S. [1994] (1995). The Language Instinct: How the Mind Creates Language. HarperCollins: New York, NY, USA. ISBN 0-06-097651-9
  52. Dawkins R. [1976] (1989). The Selfish Gene. Oxford University Press: New York, NY, USA, p.192. ISBN 0-19-286092-5
  53. Dennett DC. (1991). Consciousness Explained. Little, Brown, and Co: New York, NY, USA. ISBN 0-316-18066-1
  54. For example, see Rose H, Rose SPR, Jencks C. (2000). Alas, Poor Darwin: Arguments Against Evolutionary Psychology. Harmony Books. ISBN 0609605135
  55. Lotka AJ (1922a) Contribution to the energetics of evolution [PDF] Proc Natl Acad Sci USA 8:147–51
    Lotka AJ (1922b) Natural selection as a physical principle [PDF] Proc Natl Acad Sci USA 8:151–4
  56. Kauffman SA (1993) The Origin of order. Self-organization and selection in evolution. New York: Oxford University Press ISBN 0-19-507951-5
  59. Falconer DS & Mackay TFC (1996) Introduction to Quantitative Genetics Addison Wesley Longman, Harlow, Essex, UK ISBN 0-582-24302-5
  60. 60.0 60.1 Rice SH. (2004). Evolutionary Theory: Mathematical and Conceptual Foundations. Sinauer Associates: Sunderland, Massachusetts, USA. ISBN 0-87893-702-1 See esp. ch. 5 and 6 for a quantitative treatment.
  61. Hamilton WD. (1964). The genetical evolution of social behaviour I and II. Journal of Theoretical Biology 7: 1-16 and 17-52. PMID 5875341 PMID 5875340
  62. Trivers RL. (1971). The evolution of reciprocal altruism. Q Rev Biol 46: 35-57.

Further readingEdit

  • Historical
    • Kohm M (2004) A Reason for Everything: Natural Selection and the English Imagination. London: Faber and Faber. ISBN 0-571-22392-3. For review, see [8] van Wyhe J (2005) Human Nature Review 5:1-4

External linksEdit

Basic topics in evolutionary biology(edit)
Processes of evolution: evidence - macroevolution - microevolution - speciation
Modes: anagenesis - catagenesis - cladogenesis
Topics in population genetics(edit)
Selection: natural | sexual | artificial | ecological
Founders: Ronald Fisher | J.B.S. Haldane | Sewall Wright
List of evolutionary biology topics
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