Devolution [dev-uh-loo-shuh] is the notion that a species can change into a more ‘primitive’ form over time. Devolution presumes that there is a preferred hierarchy of structure and function, and that evolution must mean ‘progress’ to ‘more advanced’ organisms. This may include the idea that some modern species that have lost functions or complexity accordingly must be degenerate forms of their ancestors.

However, according to the definition of evolution, and particularly of the modern evolutionary synthesis in which natural selection leads to evolutionary adaptation, phenomena represented as instances of devolution are in every sense evolutionary. The idea of devolution is based at least partly on the presumption that ‘evolution’ requires some sort of purposeful direction towards ‘increasing complexity.’ Modern evolutionary theory poses no such presumption and the concept of evolutionary change is independent of either any increase in complexity of organisms sharing a gene pool, or any decrease, such as in vestigiality or in loss of genes.

Earlier views that species are subject to ‘racial decay,’ ‘drives to perfection,’ or ‘devolution’ are practically meaningless in terms of current (neo-)Darwinian theory. Early scientific theories of transmutation of species such as Lamarckism (the heritability of acquired characteristics) and orthogenesis (the hypothesis that life has an innate tendency to evolve in a unilinear fashion) perceived species diversity as a result of a purposeful internal drive or tendency to form improved adaptations to the environment, but according to the modern evolutionary synthesis evolution through natural selection comes about when heritable mutations happen to give a better chance of successful reproduction in the environment they arise in, while disadvantageous mutations or disadvantageous alleles (gene groups) decrease in frequency or are lost completely.

The concept of devolution requires that there be 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 their development is ‘evolutionary’ whereas change to an inferior or ‘less advanced’ structure would be called ‘devolution.’ In reality an evolutionary biologist defines all heritable changes to relative frequencies of the genes or indeed to epigenetic states (heritable gene markers) in the gene pool as evolution. All gene pool changes that lead to increased fitness in terms of appropriate aspects of reproduction are seen as (neo-)Darwinian adaptation because, 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 offer advantages in climbing trees, which some ancestors of humans did.

The concept of devolution as regress from progress relates to the ancient ideas that either life came into being through special creation or that humans are the ultimate product or goal of evolution. The latter belief is related to anthropocentrism (human supremacy), 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, if species evolve it is not a reaction to necessity, but rather that the population contains variations with traits that favor 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.

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 hooved toe. Modern humans may be evolving towards never having wisdom teeth, and already have lost most of the tail found in many other mammals – not to mention other vestigial structures, such as the vermiform appendix or the nictitating membrane.

A more accurate conception of devolution, a version that does not involve concepts of ‘primitive’ or ‘advanced’ organisms, is based on the observation that if certain genetic changes in a particular combination (sometimes in a particular sequence as well) are precisely reversed, one should get precise reversal of the evolutionary process, yielding an atavism or ‘throwback,’ whether more or less complex than the ancestors where the process began. At a trivial level, where just one or a few mutations are involved, selection pressure in one direction can have one effect, which can be reversed by new patterns of selection when conditions change. That could be seen as reversed evolution, though the concept is of not much interest because it does not differ in any functional or effective way from any other adaptation to selection pressures. As the number of genetic changes rises however, one combinatorial effect is that it becomes vanishingly unlikely that the full course of adaptation can be reversed precisely. Also, if one of the original adaptations involved complete loss of a gene, one can neglect any probability of reversal. Accordingly, one might well expect reversal of peppered moth color changes, but not reversal of the loss of limbs in snakes.

The concept of devolution or degenerative evolution was first used by scientists in the 19th century, at this time it was believed by most biologists that evolution had some kind of direction. In 1857, French physician Bénédict Morel influenced by Lamarckism claimed that environmental factors such as taking drugs or alcohol would produce degeneration in the offspring of those individuals, and would revert those offspring to a primitive state. Morel a devout Catholic had believed that mankind had started in perfection, contrasting modern humanity to the past, Morel claimed there had been ‘Morbid deviation from an original type.’ The theory of devolution, was later advocated by some biologists. According to Luckhurst (2005): ‘Darwin soothed readers that evolution was progressive, and directed towards human perfectibility. The next generation of biologists were less confident or consoling. Using Darwin’s theory, and many rival biological accounts of development then in circulation, scientists suspected that it was just as possible to devolve, to slip back down the evolutionary scale to prior states of development.

One of the first biologists to suggest devolution was Ray Lankester, he explored the possibility that evolution by natural selection may in some cases lead to devolution, an example he studied was the regressions in the life cycle of sea squirts. Lankester discussed the idea of devolution in his book ‘Degeneration: A Chapter in Darwinism’ (1880). He was a critic of progressive evolution, pointing out that higher forms existed in the past which have since degenerated into simpler forms. Lankester argued that ‘if it was possible to evolve, it was also possible to devolve, and that complex organisms could devolve into simpler forms or animals.’ Anton Dohrn also developed a theory of degenerative evolution based on his studies of vertebrates. According to Dohrn many chordates (animals with a nerve chord) are degenerated because of their environmental conditions. Dohrn claimed cyclostomes such as lampreys are degenerate fish as there is no evidence their jawless state is an ancestral feature but is the product of environmental adaptation due to parasitism. According to Dohrn if cyclotomes would devolve further then they would resemble something like an Amphioxus (lancelet).

Peter J. Bowler has written that devolution was taken seriously by proponents of orthogenesis and others in the late 19th century who at this period of time firmly believed that there was a direction in evolution. Orthogenesis was the belief that evolution travels in internally directed trends and levels. Paleontologist Alpheus Hyatt discussed the concept of devolution in his work, using the concept of ‘racial senility’ as the mechanism of devolution. Bowler defines racial senility as ‘an evolutionary retreat back to a state resembling that from which it began.’ Hyatt who studied the fossils of invertebrates believed that up to a point ammonoids (e.g. nautilus) developed by regular stages up until a specific level but would later due to unfavorable conditions descend back to a previous level, this according to Hyatt was a form of lamarckism as the degeneration was a direct response to external factors. To Hyatt after the level of degeneration the species would then become extinct, according to Hyatt there was a ‘phase of youth, a phase of maturity, a phase of senility or degeneration foreshadowing the extinction of a type.’ To Hyatt the devolution was predetermined by internal factors which organisms can neither control or reverse. This idea of all evolutionary branches eventually running out of energy and degenerating into extinction was a pessimistic view of evolution and was unpopular among many scientists of the time.

Carl H. Eigenmann an ichthyologist wrote ‘Cave vertebrates of America: a study in degenerative evolution’ (1909) in which he concluded that cave evolution was essentially degenerative. Entomologist William Morton Wheeler and Lamarckian E.W. MacBride (1866-1940) also advocated degenerative evolution. According to Macbride invertebrates were actually degenerate vertebrates, his argument was based on the idea that ‘crawling on the seabed was inherently less stimulating than swimming in open waters.’

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. 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 to that of a fish spine moving horizontally.

Johann Friedrich Blumenbach and other monogenists such as Georges-Louis Leclerc, Comte de Buffon were believers in the ‘Degeneration theory’ of racial origins the theory claims that races can degenerate into ‘primitive’ forms. Blumenbach claimed that Adam and Eve were white and that other races came about by degeneration from environmental factors such as the sun and poor diet. Buffon believed that the degeneration could be reversed if proper environmental control was taken and that all contemporary forms of man could revert to the original Caucasian race. Blumenbach claimed Negroid pigmentation arose because of the result of the heat of the tropical sun. The cold wind caused the tawny color of the Eskimos and the Chinese were fair skinned compared to the other Asian stocks because they kept mostly in towns protected from environmental factors. According to Blumenbach there are five races all belonging to a single species: Caucasian, Mongolian, Ethiopian, American and Malay. Blumenbach however stated: ‘I have allotted the first place to the Caucasian because this stock displays the most beautiful race of men.’ However, Blumenbach denied that his theory was racist, and wrote three essays claiming non-white peoples are capable of excelling in arts and sciences in reaction against racialists of his time who believed they couldn’t.

According to Christian creationists, devolution is: ‘A theory of origins based on scripture which begins with the ultimate complexity of all living things at the time of creation. This was followed by degeneration and the break down of all living things on the genetic level beginning at the Curse (Genesis 3) and continuing to this day with increased momentum.’ 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,’ 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.’

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 favor of this hypothesis than there ever has been in favor of the long popular theory that man is a developed animal.’ An early creationist to discuss devolution was ornithologist Douglas Dewar, writing about the subject of the fossil record for the carboniferous period Dewar wrote: ‘A few of the carboniferous insects were larger than any now existing; one of the dragon-flies had a wing-span of 28 inches. This suggests devolution rather than evolution!’

Young Earth creationist Ken Ham claims Adam and Eve were made into a state of perfection, with perfect DNA, no mistakes or mutations and that because of man sinning against God in Genesis of the Bible, that God cursed the ground and animals and sentenced man to die. Ham claims this is where mutations come from, and the incredible amount of genetic information that God had created at the beginning has been devolving ever since; according to Ham organisms in nature are losing genetic information. Creationists like Ham claim that mutations lead to a loss of genetic information and this is evidence for devolution. He has stated: ‘Observations confirm that mutations overwhelmingly cause a loss of information, not a net gain, as evolution requires.’

Young Earth creationist Joseph Mastropaolo, 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, ‘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.’

‘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 markers. 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.

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