Synthetic theory of evolution

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The synthetic theory of evolution explains the change of species, including the blueprint transformations ( macroevolution ), since 1950. It is the consistent extension of the classical evolution theories of Charles Darwin and Alfred Russel Wallace , extended by August Weismann , through combined knowledge of genetics , population biology , Paleontology , zoology , botany and systematics . In Darwin's work The Origin of Species (1859; 6th edition 1872), these findings, which were only discovered or developed after his death, were initially due to the research of Weismann. Up until the synthesis these disciplines were separated from each other.

The synthetic theory of evolution is sometimes confused with "neo-Darwinism". The zoologist August Weismann (1834–1914) provided the concepts for Neodarwinian theory, which evolutionary biologists further developed in the 20th century. The synthetic evolution theory was first established in 1937 by Theodosius Dobzhansky and in 1942 by Ernst Mayr and Julian Huxley . The synthetic theory of biological evolution is constantly being supplemented by new research results.

Foundations of Darwin and Wallace

Darwin and Wallace's theories suggest that evolution is a slow, long-term process of changing organisms, with natural selection recognized as a critical "driver" of species transformation. The individuals of a population differ by hereditary characteristics. Through directed natural selection , those changes that adapt their carriers better to a new environment are more frequently passed on to the next generation, so that they then dominate the population.

In detail, the theories of Darwin and Wallace consist of the following observations and conclusions, which have been largely integrated into the synthetic theory:

  • All species today descend from common ancestors. Darwin and Wallace made no statements as to whether life has a single ancestor or several.
  • The theory of gradualism , that is, the smallest variations in inheritance.
  • By Thomas Malthus observation acquired to limited growth in food supply and the limited food resources and u. a. from Malthus:
  • The observation that each individual (pair) produces more offspring than can survive and that population sizes remain stable over the long term.
  • The conclusion that natural selection is the driving force for evolution. The survival of individuals in the selection process depends on the hereditary quality of their adaptation to the environment.
  • The closed from conclusion of survival of the fittest ( survival of the fittest ). The best adapted of a species survive statistically more often, they have a higher number of reproductive offspring, ie their ability to pass on their own genes to the next generation is better than that of their competitors.

The genetics after Darwin's death

Darwin was unfamiliar with Gregor Mendel's 1866 essay. It was not rediscovered until 1900. The first findings in the field of genetics , especially Mendel's rules of inheritance, revealed mechanisms for generating genetic variability. In 1892, Weismann refuted Lamarck's thesis of inheritance of acquired traits, which Darwin (but not Wallace) had accepted. Until 1927, however, there was still disagreement as to whether the characteristics described by Mendel, which Wilhelm Johannsen called Gene in 1909 , represent a physical or theoretical unit.

The American Thomas Hunt Morgan made important contributions to the establishment of genetics and thus to the foundation of synthesis . He was able to prove the structure of chromosomes in the fruit fly ( Drosophila ) and demonstrate how genes are arranged on chromosomes. Of course, he still didn't know what genes are chemically.

Population genetic basis and key statements

Evolution is defined at the population genetic level as the change in gene frequencies in a reproductive community. The frequency of the genes determines the frequency of the associated characteristic values. If a change affects the entire species , it is called anagenesis , if it is limited to a subpopulation, a subspecies is formed and, in the long term, a species formation through splitting can result ( cladogenesis ). The reproductive isolation described by Ernst Mayr is a basic requirement for cladogenesis through allopatric speciation , otherwise it is a case of sympatric speciation (common in plants, rare in animals). The synthetic theory includes a. the following statements of evolutionary biology :

  • The flow of information for evolutionary changes always goes from genes to traits , never the other way around.
  • The direction of the changes is determined by four evolution factors:
  • The emergence of evolutionary innovations, new construction plans and systematic differences above the species level (also known as macroevolution ) differs only gradually from changes at the population level (also called microevolution ); the underlying evolutionary mechanisms are the same.

It should be emphasized that only genes are responsible for evolutionary changes, the genes of the individuals form the basis of their selection, with the phenotype being the "target" of selection. In an abstraction step, the genes of all individuals in a population are “compared”. Different variants of the same gene in different individuals of a species are called alleles ; they are the basis for the different characteristics in the phenotype. Hereditary differences between individuals are due to different alleles, and in rare exceptional cases also to different genes. Genetics at the level of an individual organism takes a back seat to considering changes in the gene pool of the entire population (i.e., reproductive community).

The characteristic features of the synthetic theory are thus:

  • Population concept and gene centrism
  • Gradualism
  • externalistic orientation towards directed selection
  • Adaptationism
  • Population dominance

The synthetic theory versus Darwin / Wallace

The synthetic theory is considered to be monocausal compared to Darwin's teaching. While this theory of the 1940s applied the mechanism of action mutation / recombination-selection-adaptation stringently, Darwin allowed additional perspectives, even if he could only explain them insufficiently. Darwin, like Lamarck , assumed that environmental factors can affect heredity. Darwin also added a question mark to the later realization that natural selection can only work on the level of the individual. Wallace Arthur sums up the comparison between “Synthesis” and Darwin's theories as follows: “Synthesis is completely different from Darwin's wonderful book. Its pluralism was lost, natural selection won the day. ”It must be countered that it was only through the synthesis of Dobzhansky et al Scientific disciplines were added, such as B. the factors of gene drift and sexual recombination , which were not yet known during Darwin's lifetime.

Founder in the 1930s and 1940s

The researchers named here in alphabetical order made important contributions to synthetic theory from their various disciplines on the basis mentioned above (Darwin-Wallace-Weismann-Mendel). From these together the theory of the 1940s was formed, which gave its name to the epoch in 1942 with Julian Huxley's book "Evolution - The Modern Synthesis". One cannot speak of a “synthesis” consistent in terms of the theory of science, but rather of a congruent theoretical structure that complements each other in its parts. The core of this theoretical building are the selection theory of Darwin and Wallace and the mathematical-statistical framework of population genetics.

scientist origin born-died Area of ​​Expertise Contribution and main work
Theodosius Dobzhansky Soviet Union 1923Soviet Union SU / USA
United States 48United States  		1900-1975 Zoology , genetics First architect of synthesis. Population genetics of the fruit fly Drosophila ; Pre-adaptation . Major epochal work: Genetics and the Origin of Species (1937)
Ronald Aylmer Fisher United KingdomUnited Kingdom GB 1890-1962 Math , statistics Got the basics of population genetics . He put the evolution theories on a population statistical foundation. Main work: The Genetical Theory of Natural Selection (1930)
JBS Haldane United KingdomUnited Kingdom GB 1892-1964 Biochemistry , genetics , psychology Traced parts of population genetics back to Mendel's rules and showed their compatibility with Darwin. Main work: The Causes of Evolution (1932)
Thomas Hunt Morgan United States 48United States United States 1866-1945 zoology During research on Drosophila , she discovered that genes are on the chromosomes. Nobel Prize in Medicine (1933)
Julian Huxley United KingdomUnited Kingdom GB 1887-1975 Zoology , genetics Relationship between evolution theories and genetics in p. Book: Evolution: The Modern Synthesis (1942); Contributions to the philosophy of the natural sciences in s. Book Religion Without Revelation .
Ernst Mayr German EmpireGerman Empire D / USA
United States 48United States  		1904-2005 Zoology , biogeography , systematics Most famous architect of synthesis. Main work: Systematics and the Origin of Species (1942). Definition of the biological species as reproductive community; Species formation through geographical and reproductive isolation ( allopatric speciation ). More than 700 scientific publications.
Bernhard Rensch German EmpireGerman Empire D. 1900-1990 Zoology , behavioral biology , philosophy Hauptwerk: The principle of geographical racial circles and the problem of speciation (1928)
George Gaylord Simpson United States 48United States United States 1902-1984 paleontology Concept of macroevolution, the rapid change of a population that is in imbalance with its environment into a new equilibrium. Main work: Tempo and Mode in Evolution (1944). Furthermore: Statistical methods to study the intercontinental migration of early mammals.
G. Ledyard Stebbins United States 48United States United States 1906-2000 Botany , genetics Most important representative of the botany side. Main work: Variation and Evolution in Plants (1950)
Sewall Wright United States 48United States United States 1889-1988 Theoretical biology , genetics Basics of population genetics ; Gene drift and adaptive landscape. The genetic drift (small populations) as a further evolutionary factor in addition to selection and sexual recombination .

Molecular biological knowledge since 1950

Even before the epoch of molecular biology, key findings should be mentioned that confirm genetics as a central pillar of synthesis. In 1943, the Luria-Delbrück experiment empirically supported the hypothesis that mutations can be understood as random in the sense that they are not a reaction to environmental changes. In 1952, the Hershey Chase experiment showed that genetic information is encoded in DNA and not in proteins . Due to advances in knowledge in biology, but also in other branches of science, such as the development of new observation and experimental technologies ( electron microscope , gel electrophoresis ), evolutionary biology is constantly being confirmed and expanded. The most important discovery of the 1950s to support theories of evolution was the clarification of the structure of DNA by Rosalind Franklin , James Watson and Francis Crick , but also the decoding of the genetic code by Marshall Warren Nirenberg and Heinrich Matthaei from 1961 onwards. The research on DNA provided in consequently the molecular basis of genetic processes and thus the knowledge about the mechanisms of evolution at the molecular level. It was recognized that in addition to point mutation of genes, the number, arrangement and composition of the genes in the chromosomes also play a role in genetic variation. The importance of the non-coding DNA segments, the introns , is being intensively researched. One only begins to understand what influence the epigenetic levels (cell nucleus, cell, cell aggregates) have on the phenotype ( systems theory of evolution and evolutionary developmental biology ).

Criticism of the synthesis and extensions

In the 1950s, the British biologist CH Waddington called for an expansion of the synthesis based on his work on epigenetics and genetic assimilation .

Doubts about the adaptation of the species arose from the neutral theory of molecular evolution by the Japanese Motoo Kimura from the late 1960s. According to his theory, most genetic mutations are neither lethal nor beneficial to fitness. So they play no role in the adaptation of species. It follows that random events such as genetic drift play a far greater role in the evolution of genetic information than changes that are driven by selection.

In the 1980s, American paleontologists Stephen Jay Gould and Niles Eldredge argued for an expanded synthesis. This demand was justified with the idea of punctualism , an explanation of discontinuous rates of change and jumps in fossil rows, as well as the observation that great evolutionary changes are formed in the selection of species. Ultimately, natural selection works at different levels, from genes to the organism in the entire species.

From the 1990s, research results from the new discipline of evolutionary developmental biology raised voices calling for embryonic development with its change processes and mechanisms to be a core component of evolutionary theory. The most extensive work on this comes from the American Mary Jane West-Eberhard . It calls for a new framework for a unified theory of evolution that takes up development, the environment and plasticity as the causal factors of evolution.

See also extended synthesis (evolution theory) .

About the terms Darwinism and Neo-Darwinism

The term Darwinism was made popular in 1889 by Alfred Russel Wallace (1823-1913) for the theory of evolution developed by Charles Darwin. The name neo-Darwinism goes back to George Romanes (1848–1895). He used it to describe Darwin's selection theory, which Weismann freed from all Lamarckian elements.

The neutral term evolutionary theories is the view of many biologists said today by negative associations loaded word neo-Darwinism preferable (Thesis System 1900): On the one hand gives the ending -ism seems dogmatic immobility, on the other hand was the parallel development of "Darwinism" to social Darwinism , which was used to justify racism , discredited the designation Darwinism and thus also neo-Darwinism; In addition, Wallace's achievements are ignored in this terminology (→ evolutionary biology ). However, some newer currents in evolutionary biology deliberately separate themselves from the “neo-Darwinian” mainstream.

literature

Started
  • Ernst Mayr : What Evolution is. Basic Books, New York 2001. (German: Ernst Mayr: Das ist Evolution. C. Bertelsmann, Munich 2003, ISBN 3-570-12013-9 .)
  • Ulrich Kutschera : Fact Evolution. What Darwin couldn't know. 3. Edition. Deutscher Taschenbuch Verlag, Munich 2010.
  • Richard Dawkins : Summit of the Improbable - Miracles of Evolution. (Orig .: Climbing Mount Improbable ). Rowohlt, Reinbek near Hamburg 1999.
deepening
  • Jürgen Haffner : Ornithology, Evolution, and Philosophy. The Life and Science of Ernst Mayr 1904-2005. Springer-Verlag, Heidelberg / Berlin 2007.
  • Julian Huxley : Evolution - The Modern Synthesis. With a foreword by M. Pigliucci et al. G. Muller. MIT Press, Cambridge 2010.
  • Thomas Junker : The Second Darwinian Revolution. History of Synthetic Darwinism in Germany 1924 to 1950. Basilisken-Presse, Marburg 2004.
  • Ulrich Kutschera: Evolutionary Biology. 4th edition. Publishing house Eugen Ulmer, Stuttgart 2015.
Extension of the synthesis and critical attitudes
  • William Arthur: Biased Embryos and Evolution. Cambridge University Press, Cambridge 2004.
  • Sean B. Carroll : Evo-Devo - The new image of evolution. Berlin 2008. (Orig. 2006). (Endless Forms Most Beautiful)
  • Dupré, John: Darwin's Legacy. (= Taschenbuch Wissenschaft. No. 1904). Suhrkamp, ​​Frankfurt 2009.
  • Scott F. Gilbert, David Epel: Ecological Development Biology. Integrating Epigenetics, Medicine and Evolution. Sinauer Ass. USA, 2009.
  • Stephen Jay Gould : Illusion Progress The Multiple Paths of Evolution. (Orig .: Full House - The Spread Excellence from Plate to Darwin. New York 1996). Fischer TB, 1999.
  • Eva Jablonka , Marion J. Lamb, Anna Zeligowski: Evolution in four dimensions: genetic, epigenetic, behavioral, and symbolic variation in the history of life. (= Life and Mind: Philosophical Issues in Biology and Psychology ). Bradford books, Cambridge, Massachusetts (USA), MIT Press, 2014, ISBN 978-0-262-52584-8 .
  • Marc Kirschner , John C. Gerhart: The Solution to Darwin's Dilemma - How Evolution Creates Complex Life. (Orig. The Plausibility of Life. 2005). Rowohlt, 2007.
  • Ulrich Kutschera: From the scale naturae to the symbiogenetic and dynamic tree of life. In: Biology Direct. 6, 2011, pp. 1-20.
  • Sandra Mitchell: Complexities - Why we are only just beginning to understand the world. Edition Unseld, Suhrkamp, ​​Frankfurt 2008.
  • Massimo Pigliucci , Gerd B. Müller (Ed.): Evolution - The Extended Synthesis. MIT Press, Cambridge 2010.
  • David Sloan Wilson : Evolution for Everyone: How Darwin's Theory Can Change the Way We Think About Our Lives. Delacorte Press, New York 2007.
  • Mary Jane West-Eberhard : Development Plasticity and Evolution. University Press, Oxford 2003.
  • NATURE Comment: Does evolutionary theory need a rethink. In: Nature. 514, October 9, 2014.

Web links

Individual evidence

  1. ^ Theodosius Dobzhansky: Genetics and the Origin of Species. Columbia University Press, New York 1937.
  2. ^ Ernst Mayr: Systematics and the Origin of Species from a Viewpoint of a Zoologist. Harvard University Press, Cambridge 1942.
  3. ^ Julian Huxley: Evolution - The Modern Synthesis. The Definitive Edition, with a Foreword by Massimo Pigliucci and Gerd B. Müller. (1942). MIT Press, Cambridge 2010.
  4. ↑ a b c d Ulrich Kutschera: Evolution. In: S. Maloy, K. Hughes, (Eds.): Brenner's Encyclopedia of Genetics. Vol. 2, Elsevier, New York 1937, pp. 541-544.
  5. ↑ Charles Darwin: The Origin of Species. (1872). after d. 6th edition. Nikol-Verlag, 2008.
  6. ↑ Ulrich Kutschera: Darwin-Wallace principle of natural selection. In: Nature. Volume 453, 2008, p. 27, doi: 10.1038 / 453027b , full text (PDF) ( Memento from January 9, 2014 in the Internet Archive ).
  7. ↑ Charles Darwin: The Origin of Species. 1872, graphic p. 152f u, p. 583.
  8. ↑ Charles Darwin: The Origin of Species. 1872, chap. 2
  9. ↑ Charles Darwin: The Origin of Species. 1872, pp. 26, 28, 38, 98.
  10. ↑ Charles Darwin: The Origin of Species. 1872, chap. 4th
  11. ↑ Charles Darwin: The Origin of Species. (1872). Cape. 4. Darwin did not use the term until the 5th edition (1869). He took it over from Herbert Spencer .
  12. ↑ Charles Darwin: In his letter Darwin to Asa Gray of 1857 all elements of his theory are summarized in 1857.
  13. ↑ Gabriele Werner-Felmeyer: The caution of the turtles. University Press, Berlin 2007.
  14. ↑ Stephen J. Gould: The Panda's Thumb: Considerations on Natural History. (= Suhrkamp Taschenbuch. No. 789). Frankfurt 1989.
  15. ^ A b Massimo Pigliucci: The Proper Role of Population Genetics in Modern Evolutionary Theory. In: Biological Theory. 3, 2008, pp. 316-324.
  16. ↑ Charles Darwin: The Descent of Man. (1871). Fischer Paperback, 2009, p. 38.
  17. ↑ Charles Darwin: The Origin of Species. (1872). after d. 6th edition. Nikol-Verlag, 2008 z. B, p. 116.
  18. ^ Wallace Arthur: Biased Embryos and Evolution. University Press, Cambridge 2004, p. 34.
  19. ^ Julian Huxley: Evolution - The Modern Synthesis. New edition MIT Press, Cambridge 2010. (with foreword by M. Pigliucci and G. Müller)
  20. ^ Alan C. Love: Rethinking the Structure of Evolutionary Theory for an Extended Synthesis. In: M. Pigliucci, G. Müller (2010).
  21. ^ Werner Callebaut: The Dialectics of Dis / Unity in the Evolutionary Synthesis and its Extensions. In: M. Pigliucci, G. Müller: Evolution - The Extended Synthesis. MIT Press, Cambridge 2010, p. 450.
  22. ↑ Thomas Junker: The Second Darwinian Revolution - History of Synthetic Darwinism in Germany 1924-1950. Basilisken-Presse, Marburg 2004, p. 366.
  23. ^ Adam S. Wilkins: Waddington's Unfinished Critique of Neo-Darwinian Genetics: Then and Now . In: Biological Theory . tape 3 , no. 3 , 2008, p. 224–232 , doi : 10.1162 / biot.2008.3.3.224 .
  24. ↑ Massimo Pigliucci et al: Phenotypic plasticity and evolution by genetic assimilation . In: Journal of Experimental Biology . tape 209 , 2006, pp. 2362-2367 , doi : 10.1242 / jeb.02070 ( biologists.org ).
  25. ^ S. Huang: The molecular and mathematical basis of Waddington's epigenetic landscape: A framework for post-Darwinian biology? In: BioEssays. 34, 2011, pp. 149-157.
  26. ↑ M. Kimura: The Neutral Theory of Molecular Evolution. Cambridge University Press, 1983.
  27. ↑ Stephen Jay Gould: Is a New and General Theory of Evolution Emerging? In: Paleobiology. Vol. 6, No. 1, 1980, pp. 119-130.
  28. ↑ Stephen Jay Gould: Darwinism and the Expansion of Evolutionary Theory . In: Science . tape 216 , no. 4544 , 1982, pp. 380-387 , doi : 10.1126 / science.7041256 .
  29. ↑ A More Modern Synthesis. In: American Scientist.
  30. ↑ Geerat J Vermeij: Unfinished Synthesis: Biological Hierarchies and Modern Evolutionary Thought by Niles Eldredge . In: The Quarterly Review of Biology . tape 62 , no. 1 , 1987, pp. 79-80 , doi : 10.1086 / 415312 .
  31. ^ Mary Jane West-Eberhard: Developmental Plasticity and Evolution. Oxford University Press, 2003.
  32. ↑ Gerhard Roth: The unpredictable order. Chaos, chance and selection in nature. In: Spectrum of Science. No. 12, 1993, p. 132, (full text)