Reductive evolution

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Under Reductive Evolution , also Regressive Evolution or degenerative evolution called , refers to the regression of a feature in the course of phylogeny ( phylogeny ). The processes involved primarily include the loss of features. Examples would be: regression of eyes in cave animals , loss of antibiotic resistance in bacteria that are no longer exposed to them in their environment, loss of black color morphs in industrial melanism after the reduction in soot pollution in the English coalfield.

Often a more or less inoperable residue, a rudiment , remains at first . In addition, cases must be taken into account in which a trait developed in an ancestor but later lost is developed again in some descendants, i.e. the direction of development is actually (at least apparently) reversed.

Some evolutionary biologists avoid the term because they believe it leads to paradoxes. According to this view, evolution only ever takes place in one direction. The loss of traits never reverts to the original phylogenetic states of the traits, since evolution is irreversible, at least on the genetic level ( Dollo's law ). Organisms that lack a certain trait are therefore only outwardly similar to their ancestors without this trait, but have their own genetic makeup that helps determine their future evolutionary development. Many other evolutionary biologists consider the term to be justified, provided that these processes are kept in mind, i.e. that there is no actual reversal of the development over time. In this form, the term is widely used in scientific texts.

True regressive evolution, in which a trait that has disappeared, is difficult to distinguish from parallel, or convergent , evolution, in which a similar trait is acquired independently a second time with changed selection pressure . In this case, the similarity to the status of the trait in the ancestor is only external, but the genetic basis is different. Characteristics can actually reappear if the genetic makeup necessary for their formation has not been lost, but has only been suppressed by processes of gene regulation or deactivated by gene silencing . In the case of very simple point mutations as the cause, actual reverse mutations (i.e. new mutations that exactly restore the old sequence) are also possible. It is to be expected that functionless DNA sequences will be destroyed more or less quickly by selectively neutral mutations. However, this does not apply if a characteristic has been acquired through gene recruitment of a cis element or another regulatory factor . The patterns on the wings of butterflies and other insects are controlled by regulatory mechanisms that have a different, fundamental meaning elsewhere in the organism (a case of pleiotropy ). If such a characteristic is suppressed, in which such a genetic “switch” is lost, an identical, or at least very similar, development with the reacquisition of the factor is relatively plausible.

Reductive evolution occurs especially when the environmental conditions of an organism change massively, so that previously vital complex organs lose their meaning. This applies, for example, to the evolution of endoparasites that live inside their host and no longer need numerous protective and sensory organs here. Another well-studied example is eye loss in cave fish . In the case of the Mexican species Astyanax mexicanus , for example, local populations (or species) that live in surface waters and closely related local populations (or species) living in caves are known that have regressed the eyes.

Individual evidence

  1. ↑ Michael Dzwillo: Principles of Evolution. Phylogenetics and Systematics. (Teubner study books of biology). Springer Verlag, 2013. ISBN 978-3-322-96708-4 , therein Chapter 13 Regressive Evolution, page 105 ff.
  2. ^ Megan L. Porter & Keith A. Crandall (2003): Lost along the way: the significance of evolution in reverse. TREE Trends in Ecology and Evolution 18 (10): 541-547.
  3. ↑ a b Q.BC Cronk (2009): Evolution in Reverse Gear: The Molecular Basis of Loss and Reversal. Cold Spring Harbor Symposia on Quantitative Biology 74: 259-266. doi : 10.1101 / sqb.2009.74.034

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