In common parlance, "devolution", "de-evolution", or backward evolution is the notion that a species can change into a more "primitive" form. It is associated with the idea that evolution is supposed to make species more advanced, and that some modern species have lost functions or complexity and seem to be degenerate forms of their ancestors. This view is rejected by modern evolutionary theory, in which adaptation arises from natural selection of forms best suited to the environment, and so can lead to loss of features when these features are costly to maintain. Thus for cave dwelling animals, the loss of eyes arises because it is an advantage, not degeneracy.[1] In pre-evolutionary ideas of essentialism following on from Plato's Theory of Forms, species were seen as pure unchanging types. Essentialism is rejected when genetic variation within kind is understood. The concept of created kinds can lead creationists to argue that genetic mutations are "devolution" away from the created type. Evolutionists prefer population genetics and what Ernst Mayr calls "population thinking" in defining species.[2]

The idea of devolution can arise from thinking that "evolution" requires some sort of purposeful direction towards "increasing complexity". Modern evolution theory accepts the possibility of decreasing complexity, as in vestigiality, in the course of evolutionary change,[3] but earlier views that species are subject to "racial decay"or "drives to perfection" or "devolution" have been rejected.[4] Early scientific theories of transmutation of species such as Lamarckism and orthogenesis perceived species diversity as a result of a purposeful internal drive or tendency to form improved adaptations to the environment, but in the the modern evolutionary synthesis evolution through natural selection comes about when random heritable mutations happen to give a better chance of successful reproduction in the environment they arise in, while the many disadvantageous mutations are lost.

Concepts underlying ideas of devolutionEdit

Devolution presumes that there is somehow a preferred hierarchy of structure and function, and that evolution must mean "progress" to "more advanced" organisms. For example, it could be said that "feet are better than hooves" or "lungs are better than gills", so that change to the "less advanced" structure would be called "devolution". A modern biologist sees all such changes as evolution, since for the organisms possessing the changed structures, each is a useful adaptation to their circumstances. For example, hooves have advantages for running quickly on plains, which benefits horses, and feet have advantages in climbing trees, which ancestors of humans did.[3]

The concept of devolution as regress from progress relates to the ancient idea that humans are the ultimate product or goal of evolution. This belief is related to anthropocentrism, the idea that human existence is the point of all universal existence. Such thinking can lead on to the idea that species evolve because they "need to" in order to adapt to environmental changes. Biologists refer to this misconception as teleology, the idea of intrinsic finality that things are "supposed" to be and behave a certain way, and naturally tend to act that way to pursue their own good. From a biological viewpoint, when species evolve it is not a reaction to necessity, but rather that the population contains variations with traits that favour their natural selection. This view is supported by the fossil record which demonstrates that roughly ninety-nine percent of all species that ever lived are now extinct.[3]

People thinking in terms of devolution commonly assume that progress is shown by increasing complexity, but biologists studying the evolution of complexity find evidence of many examples of decreasing complexity in the record of evolution. The lower jaw in fish, reptiles and mammals has seen a decrease in complexity, if measured by the number of bones. Ancestors of modern horses had several toes on each foot; modern horses have a single hoofed toe. Modern humans may be evolving towards never having wisdom teeth, and already have lost the tail found in many other mammals - not to mention other vestigial structures, such as the vermiform appendix or the nictitating membrane.[3]

Dollo's lawEdit

Complex organs evolve in a lineage over many generations, and once lost they are unlikely to re-evolve. This observation is sometimes generalized to a hypothesis known as Dollo's law, which states that evolution is not reversible. This does not mean that similar engineering solutions cannot be found by natural selection. For instance the tail of the cetacea--whales, dolphins and porpoises which are evolved from formerly land-dwelling mammals—is an adaptation of the spinal column for propulsion in water. Unlike the tail of the mammal's marine ancestor, the Sarcopterygii, and the other teleosts, which move from side to side, the cetacean's tail moves up and down as it flexes its mammalian spine, but the function of the tail in providing propulsion is remarkably similar.

Use of the term by opponents of evolutionismEdit

Creationism and intelligent design sometimes discuss a concept called devolution. Examples include Mastropaulo,[5] who argues that "Change over time, 'definition one' of evolution, actually describes devolution to extinction, the exact opposite of evolution.... actual epidemiological data from human genetic disorders and fatal birth defects, identify 'natural selection,' the alleged 'primary mechanism' for evolution, as actually a mechanism for devolution to extinction, the exact opposite of evolution." and elsewhere,[6] "Evolution is the development of an organism from its chemicals or primitive state to its present state. Devolution is the sequence toward greater simplicity or disappearance or degeneration."

The term was used in the play Inherit the Wind (a parable that fictionalizes the 1925 Scopes "Monkey" Trial), when the character of Matthew Brady (representative of William Jennings Bryan) argued that "Ladies and gentleman, devolution is not a theory but a cold fact ... the ape devolved from man",[7] mocking evolutionary theory by offering an alternative he considers just as plausible. During the Scopes Trial itself, a report in The New York Times said "After flocking to view the monkeys, Dayton has decided that it was not man who evolved from the anthropoid, but the anthropoid which devolved from man; and it points now at the two chimpanzees and the "missing link" to prove the assertion".[8] The suggestion of ape degenerating from "man" had already been brought up by the early young-earth creationist George McReady Price in a work published before the trial:

Accordingly, by every just rule of comparison and analogy, we may well declare that if there is any blood relationship between man and the anthropoid apes, it is the latter which have degenerated from the former, instead of the former having developed from the latter. I do not say that this is the true solution of this enigma; but I do say that there is far more scientific evidence in favour of this hypothesis than there ever has been in favour of the long popular theory than man is a developed animal.[9]

Streamlining evolutionEdit

"Devolution", the verb "devolve" and the past participle "devolved" are all common terms in science fiction for changes over time in populations of living things that make them less complex and remove some of their former adaptations. The terminology used herein is nontechnical, but the phenomenon is a real but counter-intuitive one, more accurately known as streamlining evolution. Since the development and maintenance of a feature such as an organ or a metabolite has an opportunity cost, changes in the environment that reduce the utility of an adaptation may mean that a higher evolutionary fitness is achieved by no longer using the adaptation, thus better using resources. This requires a mutation that inactivates one or more genes, perhaps by a change to DNA methylation or a methionine codon. Streamlining evolution allows evolution to remove features no longer of much/any use, like scaffolding on a completed bridge.

However, "devolution" in practice typically refers to changes that occur from a problem no longer existing rather than superior solutions existing. For instance, of the several hundred known species of animal that live their entire lives in total darkness, most have non-functional eyes rather than no eyes. This is due, for instance, to deterioration of the optic nerve. It occurs because mutations that prevent eye formation have low probability. However, several eyeless animal species, such as the Kauai cave wolf spider, who live in total darkness, and whose ancestry mostly had eyes, do exist. Together with gene duplication, streamlining evolution makes evolution surprisingly able to produce radical changes, despite being limited to successive, slight modifications.

See alsoEdit

Notes and citationsEdit

  1. TalkOrigins Archive response to Creationist claims - Claim CB932: Evolution of degenerate forms
  2. "Evolution and Philosophy: Why are natural kinds supposed to stay fixed?". Retrieved 2010-01-18. 
  3. 3.0 3.1 3.2 3.3 Michael J. Dougherty. Is the human race evolving or devolving? Scientific American July 20, 1998.
  4. "Darwin's precursors and influences: Glossary". Retrieved 2010-01-18. 
  5. Biology vs Evolution, Joseph Mastropaolo, Ph.D., Creation Research Society Quarterly 38: 151-158, 2001
  6. Biology Eliminates Evolution and Confirms Genesis (pdf) (google cache [1])
  7. Raymond Weschler (2005). [ "Inherit the Wind (Drama) ( 1960)"] (PDF). – The English Learner Movie Guides. p. 10. Retrieved 2010-01-18. 
  8. Curator (1995). "The Scopes "Monkey Trial," or "A 1925 Media Circus"". Borndigital. Retrieved 2010-01-18. 
  9. George McReady Price, The Phantom of Organic Evolution, New York: New York: Fleming H. Revell, 1924, reprinted in Selected Works of George McCready Price, ed. Ronald L. Numbers, New York: Garland Publishing, 1995, ISBN 0-8153-1808-1. volume 7 of the series Creationism in Twentieth Century America. Chapter IX Section V, page 210-211 (pages 446-447 of reprint). Italics in original.
pt:Involução (falácia biológica)

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