AskDefine | Define orthogenesis

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Noun

  1. A series of similar mutations in succesive generations, producing evolutionary change

Extensive Definition

Orthogenesis, orthogenetic evolution, progressive evolution or autogenesis, is the hypothesis that life has an innate tendency to move in a unilinear fashion due to some internal or external "driving force". The hypothesis is based on essentialism and cosmic teleology and proposes an intrinsic drive which slowly transforms species. George Gaylord Simpson (1953) in an attack on orthogenesis called this mechanism "the mysterious inner force". Classic proponents of orthogenesis have rejected the theory of natural selection as the organising mechanism in evolution, and theories of speciation for a rectilinear model of guided evolution acting on discrete species with "essences". The term orthogenesis was popularised by Theodor Eimer, though many of the ideas are much older (Bateson 1909).
Many sources mix this heterodox view of evolution with another - that evolution is proceeding to some long term or ultimate goal; the result are definitions that state "orthogenesis proposes that evolution moves in a unilinear fashion towards a perfect goal". While it is true that early and famous examples of orthogenesis often conflated these two ideas (e.g. Jean-Baptiste Lamarck's theory of evolution), and that these two ideas are buried just below the surface of Intelligent design, it is important to recognize that these are in fact two separate ideas that are rejected by mainstream science: the latter idea of goal-oriented evolution is better understood as a form of teleology. The distinction can be seen when we recognize that orthogenesis is inherent in the theories of German biologist Ernst Haeckel and American paleontologist Richard Swann Lull. Both scientists proposed mechanisms whereby evolution proceeded in unilinear fashion, but neither saw goals (instead they made pseudo-scientific appeals to unknown genetic driving processes). Noticing this is important, because similar flaws recurrently resurface at the fringes of science (typically taking the form of new, mysterious molecular drives that supposedly are pushing phenotypic evolution in certain directions or forcing the formation of new species).
The orthogenesis hypothesis had a significant following in the 19th century when a number of evolutionary mechanisms, such as Lamarckism, were being proposed. Jean-Baptiste Lamarck himself accepted the idea, and it had a central role in his theory of inheritance of acquired characteristics, the hypothesised mechanism of which resembled the "mysterious inner force" of orthogenesis. Other proponents of orthogenesis included Leo Berg, philosopher Henri Bergson and, for a time, the paleontologist Henry Fairfield Osborn. Orthogenesis was particularly accepted by paleontologists who saw in their fossils a directional change, and in invertebrate paleontology thought there was a gradual and constant directional change. Those who accepted orthogenesis in this way, however, did not necessarily accept that the mechanism that drove orthogenesis was teleological. In fact, Darwin himself rarely used the term "evolution" now so commonly used to describe his theory, because in Darwin's time, evolution usually was associated some sort of progressive process like orthogenesis, and this had been common usage since at least 1647.
Autogenesis is a specific version of orthogenesis which also incorporates spontaneous generation, the refuted hypothesis that each species is created by its own abiogenesis or special creation event.

Collapse of the hypothesis

The orthogenesis hypothesis began to collapse when it became clear that it could not explain the patterns found by paleontologists in the fossil record, which was non-linear with many complications. The hypothesis was generally abandoned when no mechanism could be found that would account for the process, and the theory of evolution by natural selection became the prevailing theory of evolution. The modern evolutionary synthesis, in which the genetic mechanisms of evolution were discovered, refuted the hypothesis for good. As more was understood about these mechanisms it became obvious that there was no possible naturalistic way in which the newly discovered mechanism of heredity could be far-sighted or have a memory of past trends.
The orthogenetic hypothesis, however, died hard. Even Darwin was at first not opposed to orthogenic thinking, as this quote from the 1911 Encyclopedia Britannica demonstrates:
A few hung on to the orthogenesis hypothesis as late as the 1950s by claiming that the processes of macroevolution, the long term trends in evolution, were distinct from the processes of microevolution (genetic variation and natural selection) which were by then well understood and it was known they could not behave in an orthogenetic manner. Teilhard de Chardin, a Jesuit paleontologist, in The Phenomenon of Man (a book influential among non-scientists that was published four years after his death in 1959) argued for evolution aiming for the "omega point", while putting man at the center of the universe and accounting for original sin (Dennett 1995, von Kitzing 1998). This form of orthogenesis has now also been abandoned as more about evolutionary processes has been discovered (Wilkins 1997).
The refutation of orthogenesis had some ramifications in the field of philosophy, as it refuted the idea of teleology as first postulated by Aristotle and accepted by Immanuel Kant, who had greatly influenced many scientists. Before the scientific and philosophical revolution that began with Charles Darwin's ideas, the prevailing philosophy was that the world was teleological and purposeful, and that science was the study of God's creation. The refutation of these concepts have led to a shift in what science and scientists are perceived to be.

Modern co-opted usage

Though teleological linear evolution has been refuted, it is not true that evolution never proceeds in a linear way, reinforcing characteristics, in certain lineages at times, for example, during a period of slow, sustained environmental change, but such examples are entirely consistent with the modern neo-Darwinian theory of evolution. These examples have sometimes been referred to as orthogenetic (e.g. by Jacobs et al 1995 & Woodley 2006) but are not strictly orthogenetic, and simply appear as linear and constant changes because of environmental and molecular constraints on the direction of change.

See also

References

Sources

  1. Bateson, William, 1909. Heredity and variation in modern lights, in Darwin and Modern Science (A.C. Seward ed.). Cambridge University Press. Chapter V. E-book.
  2. Dennett, Daniel, 1995. Darwin's Dangerous Idea. Simon & Schuster.
  3. Huxley, Julian, 1942. The Modern Evolutionary Synthesis, London: George Allen and Unwin.
  4. Jacobs, Susan C., Allan Larson & James M. Cheverud, 1995. Phylogenetic Relationships and Orthogenetic Evolution of Coat Color Among Tamarins (Genus Saguinus). Syst. Biol. 44(4):515--532, Abstract.
  5. Mayr, Ernst, 2002. What Evolution Is, London: Weidenfeld and Nicolson.
  6. Simpson, George G., 1957. Life Of The Past: Introduction to Paleontology. Yale University Press, p.119.
  7. Wilkins, John, 1997. What is macroevolution?. Talk Origins archive http://www.talkorigins.org/faqs/macroevolution.html (14:08 UTC, Oct 13 2004)
  8. Woodley, Michael A., 2006. The Limits of Ecology: New Perspectives from a Theoretical Borderland. Abramis Academic Press.
orthogenesis in German: Orthogenese
orthogenesis in Spanish: Ortogénesis
orthogenesis in French: Orthogenèse
orthogenesis in Japanese: 定向進化説
orthogenesis in Portuguese: Ortogénese
orthogenesis in Polish: Ortogeneza
orthogenesis in Russian: Ортогенез
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