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Modern evolutionary synthesis

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Modern evolutionary synthesis

Charles Darwin
Gregor Mendel
Ronald Fisher
Ernst Mayr

The modern evolutionary synthesis (known as the new synthesis, the modern synthesis, the evolutionary synthesis, millennium synthesis or the neo-Darwinian synthesis) is a 20th-century synthesis of ideas from several fields of biology that provides an account of evolution which is widely accepted. [1]

The synthesis, produced between 1936 and 1947, reflects the consensus about how evolution proceeds.[2] The previous development of nineteenth century evolutionary ideas by Charles Darwin, Gregor Mendel and others and the population genetics, between 1918 and 1932, was a stimulus, as it showed that Mendelian genetics was consistent with natural selection and gradual evolution. The synthesis is still, to a large extent, the current paradigm in evolutionary biology.[3]

The modern synthesis solved difficulties and confusions caused by the specialisation and poor communication between biologists in the early years of the 20th century. At its heart was the question of whether Mendelian genetics could be reconciled with gradual evolution by means of natural selection. A second issue was whether the broad-scale changes (macroevolution) seen by palaeontologists could be explained by changes seen in local populations (microevolution).

The synthesis included evidence from biologists, trained in genetics, who studied populations in the field and in the laboratory. These studies were crucial to evolutionary theory. The synthesis drew together ideas from several branches of biology which had become separated, particularly genetics, cytology, systematics, botany, morphology, ecology and paleontology.

G. Ledyard Stebbins.


  • Summary of the modern synthesis 1
  • Developments leading up to the synthesis 2
    • 1859–1899 2.1
    • 1900–1915 2.2
    • The foundation of population genetics 2.3
  • The modern synthesis 3
  • Further advances 4
  • After the synthesis 5
    • Understanding of Earth history 5.1
    • Symbiotic origin of eukaryotic cell structures 5.2
    • Trees of life 5.3
    • Evolutionary developmental biology 5.4
    • Fossil discoveries 5.5
    • Horizontal gene transfer 5.6
  • See also 6
  • References 7
  • Bibliography 8
  • Further reading 9
  • External links 10

Summary of the modern synthesis

The modern synthesis bridged the gap between the work of experimental geneticists and naturalists, and paleontologists. It states that:[4][5][6]

  1. All evolutionary phenomena can be explained in a way consistent with known genetic mechanisms and the observational evidence of naturalists.
  2. Evolution is gradual: small genetic changes regulated by natural selection accumulate over long periods. Discontinuities amongst species (or other taxa) are explained as originating gradually through geographical separation and extinction. This theory contrasts with the saltation theory of William Bateson (1894).[7]
  3. Natural selection is by far the main mechanism of change; even slight advantages are important when continued. The object of selection is the phenotype in its surrounding environment.
  4. The role of genetic drift is equivocal. Though strongly supported initially by Dobzhansky, it was downgraded later as results from ecological genetics were obtained.
  5. Thinking in terms of populations, rather than individuals, is primary: the genetic diversity existing in natural populations is a key factor in evolution. The strength of natural selection in the wild is greater than previously expected; the effect of ecological factors such as niche occupation and the significance of barriers to gene flow are all important.
  6. In palaeontology, the ability to explain historical observations by extrapolation from microevolution to macroevolution is proposed. Historical contingency means explanations at different levels may exist. Gradualism does not mean constant rate of change.

The idea that speciation occurs after populations are reproductively isolated has been much debated. In plants, polyploidy must be included in any view of speciation. Formulations such as 'evolution consists primarily of changes in the frequencies of alleles between one generation and another' were proposed rather later. The traditional view is that evolutionary developmental biology (evo-devo) played little part in the synthesis,[8] but an account of Gavin de Beer's work by Stephen J. Gould suggests he may be an exception.[9]

Developments leading up to the synthesis


Charles Darwin's neo-Darwinism to refer to the version of evolution advocated by Alfred Russel Wallace and August Weismann with its heavy dependence on natural selection.[11] Weismann and Wallace rejected the Lamarckian idea of inheritance of acquired characteristics, something that Darwin had not ruled out.[12]

Weismann's idea was that the relationship between the hereditary material, which he called the germ plasm (German, Keimplasma), and the rest of the body (the soma) was a one-way relationship: the germ-plasm formed the body, but the body did not influence the germ-plasm, except indirectly in its participation in a population subject to natural selection. Weismann was translated into English, and though he was influential, it took many years for the full significance of his work to be appreciated.[13] Later, after the completion of the modern synthesis, the term neo-Darwinism came to be associated with its core concept: evolution, driven by natural selection acting on variation produced by genetic mutation, and genetic recombination (chromosomal crossovers).[11]


Gregor Mendel's work was re-discovered by Hugo de Vries and Carl Correns in 1900. News of this reached William Bateson in England, who reported on the paper during a presentation to the Royal Horticultural Society in May 1900.[14] It showed that the contributions of each parent retained their integrity rather than blending with the contribution of the other parent. This reinforced a division of thought, which was already present in the 1890s.[15] The two schools were:

  • Saltationism (large mutations or jumps), favored by early Mendelians who viewed hard inheritance as incompatible with natural selection[16]
  • Mendelism predicted.

The relevance of Mendelism to evolution was unclear and hotly debated, especially by Bateson, who opposed the biometric ideas of his former teacher Weldon. Many scientists believed the two theories substantially contradicted each other.[17] This debate between the biometricians and the Mendelians continued for some 20 years and was only solved by the development of population genetics.

Drosophila melanogaster, which helped establish the link between Mendelian genetics and the chromosomal theory of inheritance, demonstrated that rather than creating new species in a single step, mutations increased the genetic variation in the population.[18]

The foundation of population genetics

The first step towards the synthesis was the development of population genetics. R. A. Fisher, J. B. S. Haldane, and Sewall Wright provided critical contributions. In 1918, Fisher produced the paper "The Correlation Between Relatives on the Supposition of Mendelian Inheritance,"[19] which showed how the continuous variation measured by the biometricians could be the result of the action of many discrete genetic loci. In this and subsequent papers culminating in his 1930 book The Genetical Theory of Natural Selection,[20] Fisher was able to show how Mendelian genetics was, contrary to the thinking of many early geneticists, completely consistent with the idea of evolution driven by natural selection.[21] During the 1920s, a series of papers by Haldane applied mathematical analysis to real world examples of natural selection such as the evolution of industrial melanism in peppered moths.[21] Haldane established that natural selection could work in the real world at a faster rate than even Fisher had assumed.[22]

Sewall Wright focused on combinations of genes that interacted as complexes, and the effects of inbreeding on small relatively isolated populations, which could exhibit genetic drift. In a 1932 paper, he introduced the concept of an adaptive landscape in which phenomena such as cross breeding and genetic drift in small populations could push them away from adaptive peaks, which would in turn allow natural selection to push them towards new adaptive peaks.[21][23] Wright's model would appeal to field naturalists such as Theodosius Dobzhansky and Ernst Mayr who were becoming aware of the importance of geographical isolation in real world populations.[22] The work of Fisher, Haldane and Wright founded the discipline of population genetics. This is the precursor of the modern synthesis, which is an even broader coalition of ideas.[21][22][24] One limitation of the modern synthesis version of population genetics is that it treats one gene locus at a time, neglecting genetic linkage and resulting linkage disequilibrium between loci.

The modern synthesis

Theodosius Dobzhansky, an emigrant from the Drosophila pseudoobscura. He says pointedly: "Russia has a variety of climates from the Arctic to sub-tropical... Exclusively laboratory workers who neither possess nor wish to have any knowledge of living beings in nature were and are in a minority."[25] Not surprisingly, there were other Russian geneticists with similar ideas, though for some time their work was known to only a few in the West. His 1937 work Genetics and the Origin of Species[26] was a key step in bridging the gap between population geneticists and field naturalists. It presented the conclusions reached by Fisher, Haldane, and especially Wright in their highly mathematical papers in a form that was easily accessible to others. It also emphasized that real world populations had far more genetic variability than the early population geneticists had assumed in their models, and that genetically distinct sub-populations were important. Dobzhansky argued that natural selection worked to maintain genetic diversity as well as driving change. Dobzhansky had been influenced by his exposure in the 1920s to the work of a Russian geneticist Sergei Chetverikov who had looked at the role of recessive genes in maintaining a reservoir of genetic variability in a population before his work was shut down by the rise of Lysenkoism in the Soviet Union.[21][22]

E. B. Ford's work complemented that of Dobzhansky. It was as a result of Ford's work, as well as his own, that Dobzhansky changed the emphasis in the third edition of his famous text from drift to selection.[27] Ford was an experimental naturalist who wanted to test natural selection in nature. He virtually invented the field of research known as ecological genetics. His work on natural selection in wild populations of butterflies and moths was the first to show that predictions made by R. A. Fisher were correct. He was the first to describe and define genetic polymorphism, and to predict that human blood group polymorphisms might be maintained in the population by providing some protection against disease.[28]

Ernst Mayr's key contribution to the synthesis was Systematics and the Origin of Species, published in 1942.[29] Mayr emphasized the importance of allopatric speciation, where geographically isolated sub-populations diverge so far that reproductive isolation occurs. He was skeptical of the reality of sympatric speciation believing that geographical isolation was a prerequisite for building up intrinsic (reproductive) isolating mechanisms. Mayr also introduced the biological species concept that defined a species as a group of interbreeding or potentially interbreeding populations that were reproductively isolated from all other populations.[21][22][30] Before he left Germany for the United States in 1930, Mayr had been influenced by the work of German biologist Bernhard Rensch. In the 1920s Rensch, who like Mayr did field work in Indonesia, analyzed the geographic distribution of polytypic species and complexes of closely related species paying particular attention to how variations between different populations correlated with local environmental factors such as differences in climate. In 1947, Rensch published Neuere Probleme der Abstammungslehre. Die transspezifische Evolution (1959 English translation of 2nd edition: Evolution Above the Species Level).[31] This looked at how the same evolutionary mechanisms involved in speciation might be extended to explain the origins of the differences between the higher level taxa. His writings contributed to the rapid acceptance of the synthesis in Germany.[32][33]

George Gaylord Simpson was responsible for showing that the modern synthesis was compatible with paleontology in his book Tempo and Mode in Evolution published in 1944. Simpson's work was crucial because so many paleontologists had disagreed, in some cases vigorously, with the idea that natural selection was the main mechanism of evolution. It showed that the trends of linear progression (in for example the evolution of the horse) that earlier paleontologists had used as support for neo-Lamarckism and orthogenesis did not hold up under careful examination. Instead the fossil record was consistent with the irregular, branching, and non-directional pattern predicted by the modern synthesis.[21][22]

The botanist G. Ledyard Stebbins was another major contributor to the synthesis. His major work, Variation and Evolution in Plants, was published in 1950. It extended the synthesis to encompass botany including the important effects of hybridization and polyploidy in some kinds of plants.[21]

Further advances

John Maynard Smith
Richard Dawkins

The modern evolutionary synthesis continued to be developed and refined after the initial establishment in the 1930s and 1940s. The work of John Maynard Smith and others led to the development of a gene-centered view of evolution in the 1960s. The synthesis as it exists now has extended the scope of the Darwinian idea of natural selection to include subsequent scientific discoveries and concepts unknown to Darwin, such as DNA and genetics, which allow rigorous, in many cases mathematical, analyses of phenomena such as kin selection, altruism, and speciation.

In The Selfish Gene (1976), author Richard Dawkins asserts the gene is the only true unit of selection.[34] (Dawkins also attempts to apply evolutionary theory to non-biological entities, such as cultural memes, imagined to be subject to selective forces analogous to those affecting biological entities.)

Others, such as Stephen Jay Gould, reject the notion that genetic entities are subject to anything other than genetic or chemical forces, (as well as the idea evolution acts on "populations" per se), reasserting the centrality of the individual organism as the true unit of selection, whose specific phenotype is directly subject to evolutionary pressures.

In 1972, the notion of gradualism in evolution was challenged by a theory of punctuated equilibrium put forward by Gould and Niles Eldredge, proposing evolutionary changes could occur in relatively rapid spurts, when selective pressures were heightened, punctuating long periods of morphological stability, as well-adapted organisms coped successfully in their respective environments.

Discovery in the 1980s of Hox genes and regulators conserved across multiple phyletic divisions began the process of addressing basic theoretical problems relating to gradualism, incremental change, and sources of novelty in evolution. Suddenly, evolutionary theorists could answer the charge that spontaneous random mutations should result overwhelmingly in deleterious changes to a fragile, monolithic genome: Mutations in homeobox regulation could safely—yet dramatically—alter morphology at a high level, without damaging coding for specific organs or tissues.

This, in turn, provided the means to model hypothetical genomic changes expressed in the phenotypes of long-extinct species, like the Late Devonian "fish with hands," Tiktaalik, discovered in 2004.

As these discoveries suggest, the synthesis continues to undergo regular review, drawing on insights offered by both new biotechnologies and new paleontological discoveries.[35]

After the synthesis

The structure of evolutionary biology.
The history and causes of evolution (center) are subject to various subdisciplines of evolutionary biology. The areas of segments give an impression of the contributions of subdisciplines to the literature of evolutionary biology.

There are a number of discoveries in earth sciences and biology which have arisen since the synthesis. Listed here are some of those topics which are relevant to the evolutionary synthesis, and which seem soundly based.

Understanding of Earth history

The Earth is the stage on which the evolutionary play is performed. Darwin studied evolution in the context of Charles Lyell's geology, but our present understanding of Earth history includes some critical advances made during the last half-century.

  • The age of the Earth has been revised upwards. It is now estimated to be approximately 4.54 billion years old, nearly one-third of the age of the universe. The Phanerozoic (current eon) only occupies the last one-ninth of this period of time.[36]
  • Understanding of the evolution of the [40][39]
  • The identification of the first generally accepted fossils of microbial life was made by geologists. These rocks have been dated as about 3.465 billion years ago.[41] [42]
  • Information about paleoclimates is increasingly available, and being used in paleontology. One example: the discovery of massive ice ages in the Proterozoic, following the great reduction of CO2 in the atmosphere. These ice ages were immensely long, and led to a crash in microflora.[43] (See also Cryogenian period and Snowball Earth.)

Conclusion: Our present knowledge of earth history strongly suggests that large-scale geophysical events influenced macroevolution and megaevolution. These terms refer to evolution above the species level, including such events as mass extinctions, adaptive radiation, and the major transitions in evolution.[47][48]

Symbiotic origin of eukaryotic cell structures

Once symbiosis was discovered in lichen and in plant roots (rhizobia in root nodules) in the 19th century, the idea arose that the process might have occurred more widely, and might be important in evolution. Heinrich Anton de Bary invented the concept of symbiosis;[49] several Russian biologists promoted the idea;[50] Edmund Beecher Wilson mentioned it in his book The Cell in Development and Heredity (1925);[51] as did Ivan Wallin in his Symbionticism and the Origin of Species (1927);[52] and there was a brief mention by Julian Huxley in 1930;[53] all in vain because sufficient evidence was lacking. Symbiosis as a major evolutionary force was not discussed at all in the evolutionary synthesis.[54]

The role of symbiosis in cell evolution was revived partly by microbial origin: mitochondria and chloroplasts definitely, cilia, flagella and centrioles possibly, and perhaps the nuclear membrane and much of the chromosome structure as well. What is now clear is that the evolution of eukaryote cells is either caused by, or at least profoundly influenced by, symbiosis with bacterial and archaean cells in the Proterozoic.

The origin of the eukaryote cell by symbiosis in several stages was not part of the evolutionary synthesis. It is, at least on first sight, an example of megaevolution by big jumps. However, what symbiosis provided was a copious supply of heritable variation from microorganisms, which was fine-tuned over a long period to produce the cell structure we see today. This part of the process is consistent with evolution by natural selection.[58]

Trees of life

The ability to analyse sequence in Archean eon).[61]

This technique may be used to clarify relationships within any group of related organisms. It is now a standard procedure, and examples are published regularly. April 2008 sees the publication of a tree covering all the animal phyla, derived from sequences from 150 genes in 77 taxa.[62]

Early attempts to identify relationships between major groups were made in the 19th century by Ernst Haeckel, and by comparative anatomists such as Thomas Henry Huxley and E. Ray Lankester. Enthusiasm waned: it was often difficult to find evidence to adjudicate between different opinions. Perhaps for that reason, the evolutionary synthesis paid surprisingly little attention to this activity. It is certainly a lively field of research today.

Evolutionary developmental biology

What once was called embryology played a modest role in the evolutionary synthesis,[63] mostly about evolution by changes in developmental timing (allometry and heterochrony).[64] Man himself was, according to Louis Bolk, a typical case of evolution by retention of juvenile characteristics (neoteny). He listed many characters where "Man, in his bodily development, is a primate foetus that has become sexually mature."[65] Unfortunately, his interpretation of these ideas was non-Darwinian, but his list of characters is both interesting and convincing.[66]

Evolutionary developmental biology springs from clear proof that development is closely controlled by special genetic systems, and the hope that comparison of these systems will tell us much about the evolutionary history of different groups.[67][68] In a series of experiments with the fruit fly [76]

The term deep homology was coined to describe the common origin of genetic regulatory apparatus used to build morphologically and phylogenetically disparate animal features.[77] It applies when a complex genetic regulatory system is inherited from a common ancestor, as it is in the evolution of vertebrate and invertebrate eyes. The phenomenon is implicated in many cases of parallel evolution.[78]

A great deal of evolution may take place by changes in the control of development. This may be relevant to punctuated equilibrium theory, for in development a few changes to the control system could make a significant difference to the adult organism. An example is the giant panda, whose place in the Carnivora was long uncertain.[79] Apparently, the giant panda's evolution required the change of only a few genetic messages (5 or 6 perhaps), yet the phenotypic and lifestyle change from a standard bear is considerable.[80][81] The transition could therefore be effected relatively swiftly.

Fossil discoveries

Since the late 20th century, there have been excavations in parts of the world which had scarcely been investigated before. Also, there is fresh appreciation of fossils discovered in the 19th century, but then denied or deprecated: the classic example is the multicellular life. The interpretation of this fauna is still in flux.

Many outstanding discoveries have been made, and some of these have implications for evolutionary theory. The discovery of feathered dinosaurs and early birds from the Early Cretaceous of Liaoning Province in northeast China have convinced most paleontologists that birds did evolve from coelurosaurian theropod dinosaurs. Less well known, but perhaps of equal evolutionary significance, are the studies on early insect flight, on stem tetrapods from the Late Devonian,[82][83] and the early stages of whale evolution.[84]

Recent work has shed light on the evolution of

External links

  • "This book is based on a series of lectures delivered in January 1931 at the Prifysgol Cymru, Aberystwyth, and entitled 'A re-examination of Darwinism'."  

Further reading

  • The book is available from The Complete Work of Charles Darwin Online. Retrieved 2015-05-25. The Chapter VII in this edition is taken up with answering critics of natural selection.  
  • Davis, D. Dwight (1964). The Giant Panda: A Morphological Study of Evolutionary Mechanisms. Fieldiana: Zoology Memoirs 3. Chicago, IL:  
  • . Embryos and Ancestors 2nd (1940) and 3rd (1958) editions under the title  
    • —— (1951). Genetics and the Origin of Species. Columbia University Biological Series (3rd revised ed.). New York: Columbia University Press.  
  • Elewa, Ashraf M. T., ed. (2008). Mass Extintion. Berlin; Heidelberg:  
    • —— (1975). Ecological Genetics (4th ed.). London; New York:  
  • delivered in December, 1939" Silliman Lectures "This book presents an elaboration of the material which was used, in less technical and less detailed form, for presentation in eight  
  • Gould, Stephen Jay (2002).  
  • Huggett, Richard J. (1997). Catastrophism: Asteroids, Comets, and other Dynamic Events in Earth History. London; New York:  
  • Huxley, Julian (2010) [Originally published 1942].  
  • Khakhina, Liya Nikolaevna (1992).  
  • . Retrieved 2015-05-25. Internet Archive on Philosophie zoologique (1809)  
  • Laubichler, Manfred D.;  
  • Margulis, Lynn (1993). Symbiosis in Cell Evolution: Microbial Communities in the Archean and Proterozoic Eons (2nd ed.). New York:  
  • Margulis, Lynn; Fester, René, eds. (1991). Symbiosis as a Source of Evolutionary Innovation: Speciation and Morphogenesis. Cambridge, MA: MIT Press. "Based on a conference held in Bellagio, Italy, June 25-30, 1989."  
  • Mayr, Ernst (1999) [First published 1942; Cambridge, MA: Columbia University Press].  
  • Mayr, Ernst (2002) [First published in the USA in 2001 by  
  • Mayr, Ernst;  
  • Raff, Rudolf A.; Kaufman, Thomas C. (1983). Embryos, Genes, and Evolution: The Developmental-Genetic Basis of Evolutionary Change. Illustrated by Elizabeth C. Raff. New York:  
    • —— (1959). Evolution Above the Species Level (English translation of 2nd edition of Neuere Probleme der Abstammungslehre (1954)). Columbia Biological Series 19. London: Methuen Publishing.  
  • Schopf, J. William; Klein, Cornelis, eds. (1992). The Proterozoic Biosphere: A Multidisciplinary Study. Cambridge, UK; New York:  
  • Smocovitis, Vassiliki Betty (1996). Unifying Biology: The Evolutionary Synthesis and Evolutionary Biology. Princeton, NJ: Princeton University Press.  
  • van Andel, Tjeerd H. (1994). New Views on an Old Planet: A History of Global Change (2nd ed.). Cambridge, UK; New York: Cambridge University Press.  
  • Yochelson, Ellis L. (1998). Charles Doolittle Walcott: Paleontologist. Kent, OH:  


  1. ^ National Academy of Sciences 1999, p. 28: "The scientific consensus around evolution is overwhelming."
  2. ^ National Academy of Sciences 1999, p. 28: "The scientific consensus around evolution is overwhelming."
  3. ^ Mayr 2002, p. 270
  4. ^ Huxley 2010
  5. ^ Mayr & Provine 1998
  6. ^ Mayr 1982, p. 567 et seq.
  7. ^ Bateson 1894
  8. ^ Smocovitis 1996, p. 192
  9. ^ Gould 1977, p. 221–222
  10. ^ Bowler 2003, pp. 236–256
  11. ^ a b Gould 2002, p. 216
  12. ^  
  13. ^ Bowler 2003, pp. 253–256
  14. ^ Ambrose, Mike. "Mendel's Peas". Norwich, UK: Germplasm Resources Unit,  
  15. ^ Bateson 1894: The division of thought was between gradualists of the Darwinian school, and saltationists such as Bateson. Mutations (as 'sports') and polymorphisms were well known long before the Mendelian recovery.
  16. ^ Larson 2004, pp. 157–166
  17. ^ Grafen & Ridley 2006, p. 69
  18. ^ Bowler 2003, pp. 271–272
  19. ^   "Paper read by J. Arthur Thomson on July 8, 1918 to the Royal Society of Edinburgh."
  20. ^ Fisher 1999
  21. ^ a b c d e f g h Larson 2004, pp. 221–243
  22. ^ a b c d e f Bowler 2003, pp. 325–339
  23. ^ Wright 1932, pp. 356–366
  24. ^ Gould 2002, pp. 503–518
  25. ^ Mayr & Provine 1998, p. 231
  26. ^ Dobzhansky 1937
  27. ^ Dobzhansky 1951
  28. ^ Ford 1964; Ford 1975
  29. ^ Mayr 1999
  30. ^ Mayr & Provine 1998, pp. 33–34
  31. ^ Rensch 1947; Rensch 1959
  32. ^  
  33. ^ Mayr & Provine 1998, pp. 298–299, 416
  34. ^ Bowler 2003, p. 361
  35. ^  
  36. ^ Dalrymple 2001, pp. 205–221
  37. ^ van Andel 1994
  38. ^ Witze, Alexandra (July 13, 2006). "Geology: The start of the world as we know it".  
  39. ^ Schopf & Klein 1992
  40. ^ Lane 2002
  41. ^ Schopf 1999
  42. ^ Yochelson 1998
  43. ^ Knoll & Holland 1995
  44. ^ Huggett 1997
  45. ^ Hallam & Wignall 1997
  46. ^ Elewa 2008
  47. ^ The terms (or their equivalents) were used as part of the synthesis by Simpson 1984 and Rensch 1947. They were also used by some non-Darwinian evolutionists such as Yuri Filipchenko and Richard Goldschmidt. Here we use the terms as part of the evolutionary synthesis: they do not imply any change in mechanism.
  48. ^ Maynard Smith & Szathmáry 1997
  49. ^ de Bary 1879
  50. ^ Khakhina 1992
  51. ^ Wilson 1925
  52. ^ Wallin 1927
  53. ^ Huxley 1929–1930, p. 505
  54. ^ Sapp 1994
  55. ^  
  56. ^ Margulis & Fester 1991
  57. ^ Margulis 1993
  58. ^ Maynard Smith & Szathmáry 1997: The origin of the eukaryote cell is one of the seven major transitions, according to these authors.
  59. ^  
  60. ^  
  61. ^ Doolittle, W. Ford (February 2000). "Uprooting the Tree of Life" (PDF).  
  62. ^ Dunn, Casey W.; Hejnol, Andreas; Matus, David Q.; et al. (April 10, 2008). "Broad phylogenetic sampling improves resolution of the animal tree of life". Nature (London: Nature Publishing Group) 452 (7188): 745–749.  
  63. ^ Laubichler & Maienschein 2007
  64. ^ de Beer 1930
  65. ^ Bolk 1926
  66. ^ Gould 1977, p. 357: Short-list of 25 characters.
  67. ^ Raff & Kaufman 1983
  68. ^ Carroll 2005
  69. ^ Lewis 1997, pp. 247–272
  70. ^ Lawrence 1992
  71. ^ Duncan, Ian (December 1987). "The Bithorax Complex".  
  72. ^  
  73. ^  
  74. ^  
  75. ^ Gehring 1998
  76. ^ Lewis 1997, p. 266
  77. ^  
  78. ^ Shubin, Neil; Tabin, Cliff; Carroll, Sean B. (February 12, 2009). "Deep homology and the origins of evolutionary novelty". Nature (London: Nature Publishing Group) 457 (7231): 818–823.  
  79. ^  
  80. ^ Davis 1964
  81. ^ Stanley 1979, p. 157
  82. ^ Clack 2002
  83. ^ "Jenny Clack's Home Page". 
  84. ^ Both whale evolution and early insect flight are discussed in Raff 1996. These discussions provide a welcome synthesis of evo-devo and paleontology.
  85. ^ a b  
  86. ^ Lamarck 1809
  87. ^ Mivart 1871
  88. ^ Darwin 1872, pp. 186–188
  89. ^  
  90. ^ Goldschmidt 1940
  91. ^ Friedman, Matt (July 10, 2008). "The evolutionary origin of flatfish asymmetry". Nature (London: Nature Publishing Group) 454 (7201): 209–212.  
  92. ^ Richardson, Aaron O.; Palmer, Jeffrey D. (January 2007). "Horizontal gene transfer in plants".  
  93. ^ a b McDaniel, Lauren D.; Young, Elizabeth; Delaney, Jennifer; et al. (October 1, 2010). "High Frequency of Horizontal Gene Transfer in the Oceans". Science (Washington, D.C.: American Association for the Advancement of Science) 330 (6000): 50.  
  94. ^ Maxmen, Amy (September 30, 2010). "Virus-like particles speed bacterial evolution". Nature News (London: Nature Publishing Group).  
  95. ^ Gladyshev, Eugene A.;  
  96. ^ Arkhipova, Irina R.; Meselson, Matthew (August 16, 2005). "Diverse DNA transposons in rotifers of the class Bdelloidea". Proc. Natl. Acad. Sci. U.S.A. (Washington, D.C.: National Academy of Sciences) 102 (33): 11781–11786.  


See also

Some examples of HGT in Metazoa are now known. Genes in bdelloid rotifers have been found which appear to have originated in bacteria, fungi, and plants. This suggests they arrived by horizontal gene transfer. The capture and use of exogenous (~foreign) genes may represent an important force in bdelloid evolution.[95][96] The team led by Matthew S. Meselson at Harvard University has also shown that, despite the lack of sexual reproduction, bdelloid rotifers do engage in genetic (DNA) transfer within a species or clade. The method used is not known at present.

  • Transformation, the genetic alteration of a cell resulting from the introduction, uptake and expression of foreign genetic material (DNA or RNA).
  • Transduction, the process in which bacterial DNA is moved from one bacterium to another by a bacterial virus (a bacteriophage, or 'phage').
  • Bacterial conjugation, a process in which a bacterial cell transfers genetic material to another cell by cell-to-cell contact.
  • Gene transfer agent (GTA) is a virus-like element which contains random pieces of the host chromosome. They are found in most members of the Alphaproteobacteria order Rhodobacterales.[93] They are encoded by the host genome. GTAs transfer DNA so frequently that they may have an important role in evolution.[94]
    A 2010 report found that genes for antibiotic resistance could be transferred by engineering GTAs in the laboratory.[93]

The bacterial means of HGT are:

Aaron O. Richardson and Jeffrey D. Palmer state: "Horizontal gene transfer (HGT) has played a major role in bacterial evolution and is fairly common in certain unicellular eukaryotes. However, the prevalence and importance of HGT in the evolution of multicellular eukaryotes remain unclear."[92]

Most thinking in genetics has focused on vertical transfer, but there is a growing awareness that horizontal gene transfer is a significant phenomenon. Amongst single-celled organisms it may be the dominant form of genetic transfer. Artificial horizontal gene transfer is a form of genetic engineering.

Horizontal gene transfer (HGT) (or lateral gene transfer) is any process in which an organism gets genetic material from another organism without being the offspring of that organism.

Horizontal gene transfer

A recent examination of two fossil species from the Eocene has provided the first clear picture of flatfish evolution. The discovery of stem flatfish with incomplete orbital migration refutes Goldschmidt's ideas, and demonstrates that "the assembly of the flatfish bodyplan occurred in a gradual, stepwise fashion."[91] There are no grounds for thinking that incomplete orbital migration was maladaptive, because stem forms with this condition ranged over two geological stages, and are found in localities which also yield flatfish with the full cranial asymmetry. The evolution of flatfish falls squarely within the evolutionary synthesis.[85]

[90][89] put the case forward as an example of evolution by saltation, bypassing intermediate forms.Richard Goldschmidt Many years later the geneticist [88], Darwin made a concession to the possibility of acquired traits.On the Origin of Species and in the 6th edition of [87]

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