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Tuesday, January 10, 2017

Evolution vs adaptation

The word "evolution" was in use long before Darwin. Even though he did not use it in his book, he is associated with the word when we talk about biology. The reason may be that he indirectly defined it in the last paragraph of his book, that ends with "evolved":

It is interesting to contemplate a tangled bank, clothed with many plants of many kinds, with birds singing on the bushes, with various insects flitting about, and with worms crawling through the damp earth, and to reflect that these elaborately constructed forms, so different from each other, and dependent upon each other in so complex a manner, have all been produced by laws acting around us. These laws, taken in the largest sense, being Growth with reproduction; Inheritance which is almost implied by reproduction; Variability from the indirect and direct action of the conditions of life, and from use and disuse; a Ratio of Increase so high as to lead to a Struggle for Life, and as a consequence to Natural Selection, entailing Divergence of Character and the Extinction of less improved forms. Thus, from the war of nature, from famine and death, the most exalted object which we are capable of conceiving, namely, the production of the higher animals, directly follows. There is grandeur in this view of life, with its several powers, having been originally breathed by the Creator into a few forms or into one; and that, whilst this planet has gone circling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being evolved.

"Adaptation" has been used as a contrast to evolution to denote the changes of organisms that scientists before Darwin, such as Lamarck, described. But these are changes exclusively within a species. They used the observations of such changing as a proof of species constancy, e.g. that dogs can change into highly different races, but still the species is the same.

But from around 1940 there was created some confusion of this terminology. Persons behind "the modern synthesis" used "evolution" to denote changes of allele frequencies in a population. These processes do not involve any novelty, i.e. no speciation and no creation of features. They are therefore adaptations, and no evolution. Some of these persons may have allowed mutations, but then just as a way to fill up the reservoir of alleles. Richard Dawkins, who is basing his writing on adaptation, said in the Homage to Darwin debate with Lynn Margulis that for eukaryotes the ideal mutation rate is zero.

The confusive terminology is therefore still in use, and due to the popularity of his books, this may give rise to misconceptions that should be avoided. You may find some background information in this site.

2 comments:

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  2. I have seen the argument elsewhere that evolution vs adaptation is the same as macroevolution vs microevolution. In the original definition by the Russian entomologist Yuri Filipchenko this was probably clear. But the modern synthesis committee made the distinction unclear. Wikipedia defines macro- and microevolution as changes above and below the level of species.  It is further stated that microevolution is changes of allele frequencies within a species or population, i.e. it is the same as adaptation. But then they say that "Macroevolution and microevolution describe fundamentally identical processes on different time scales." That seems very strange, because then macroevolution should be the change of allele frequencies between species. This confusion was produced by Ernst Mayr and the other members of the committee. I will therefore not use these terms.

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