Lamarckism
Lamarckism is the theory that organisms can inherit traits in their offspring that they acquired during their lifetime. It is named after the French biologist Jean-Baptiste de Lamarck (1744–1829) who developed one of the first theories of evolution in the 19th century . In contrast to what has often been stated, the inheritance of acquired properties is only one aspect of Lamarck's original theory; the term Lamarckism today therefore usually does not designate Lamarck's theory as a whole.
While the concept of inheritance of acquired traits was not controversial at first and was also found in Darwin's theory of evolution (→ Darwinism ) in 1859 , it was not until 1883 that August Weismann's further development of Darwin's theory sparked a debate between neo-Darwinists and neolamarckists. This dispute was fought out not only on a scientific, but also on a sociopolitical level until the middle of the 20th century. With the development of the synthetic theory of evolution , in which the principle of natural selection could be reconciled with genetics , the dispute was decided in favor of Darwinism.
Lamarck's theory
The theory of evolution designed by Lamarck in his best-known work Philosophy Zoologique (1809) and in the later Histoire naturelle des animaux sans vertèbres (1815-1822) was one of the first attempts at a systematic theory of evolution . More recent representations characterize Lamarck's theory as an interplay of two factors:
- undirected adaptation to external changes
- linear progress on a linear ladder of complexity
Adaptation to external changes
The background for Lamarck's theory is a combination of the geological principle of uniformity and gradualism . Lamarck assumed that all natural forces working in the present have also worked in the past. Singular events, such as in Cuvier's catastrophe theory , play no role; nature changes gradually and does not make abrupt leaps.
According to Lamarck, it is precisely these gradual changes in the environment that drive evolution: A changed environment leads to the habits of the organisms living in it also changing, which in turn results in the organisms themselves changing. According to his theory , somatic modifications caused by changed habits would be passed on to the next generations. This point in Lamarck's theory is known today as "Lamarckism" or "soft inheritance" and - in contrast to Lamarck's other views - has not been forgotten.
Today it is mostly illustrated by the example of the giraffe , which had to stretch for high leaves from trees in a dry, inhospitable environment in order to feed. As a result, the long neck developed over many generations. Lamarck used this example only as one of many; for him it did not have the central position that it has today in many presentations of his theory.
Lamarck assumed an inheritance of acquired traits, which later turned out to be incorrect. Lamarck was not yet able to distinguish between the genetic information in the cells of the body tissue, which cannot be passed on to the offspring, and the genetic information in the egg cells and sperm , which is the only one inherited. The genes had not yet been discovered at the time. Today the prevailing view is that acquired traits are not inherited, since the genetic information is only passed on to the next generation via the germ line , and that recombination and mutation are responsible for the development of new traits. The giraffe example enjoys constant popularity because it can also be used to refute Lamarck as an example of a result of a transformative selection .
Linear progress
Since the “Lamarckist” part of Lamarck's theory, in which the organisms adapt to the undirected external changes in a kind of random movement , cannot explain the increasing complexity of the organisms over time, a consistent theory of evolution requires further additions.
Lamarck's solution to this problem is to adopt a second evolutionary force. He postulates the existence of a linear taxonomic scale of complexity on which all organisms can be classified and at the top of which is man. All organisms have an instinct for perfection, through which they climb the ladder of complexity through gradual changes. This process can happen even without changes in the environment, so it is decoupled from “soft inheritance”. Lamarck does not elaborate on the mechanisms for this process, he only gives vague “movements of liquids” and “vital forces” as an explanation.
Lamarck explains the problem of why there are also lower forms of life when all organisms move up the complexity scale with a constant spontaneous generation of lower forms of life. He does not give a specific mechanism for this either.
In contrast to Darwin, Lamarck did not postulate a doctrine of descent, but rather each recent species has its own evolutionary line. The most highly evolved organisms first arose through spontaneous generation, the lower organisms later. According to Lamarck, the evolutionary line to humans is therefore the longest and therefore the oldest.
The factors in interaction
The biodiversity observed in nature , as Lamarck had to admit, can hardly be explained by a linear scale of complexity, which can therefore only be an idealization. In reality, the linear progress of the species is to a certain extent "disturbed" by the adaptive adaptation of the species to the changing environment. There is a constant interplay between forward and sideways evolution.
An important problem in Lamarck's time, stimulated by the discovery of fossils , was the possible extinction of species. Lamarck largely denied that species can become extinct. A species thought to be extinct could either continue to exist in parts of the world that are still unknown, or it could have changed so much through adaptation that it is no longer recognized. Only the possibility that individual species could be exterminated by humans, Lamarck considered in a "prophetic" manner.
reception
Lamarck received few reactions to his theory of evolution during his lifetime. This was partly due to the fact that, in the style of past centuries, he was more a natural philosopher than a natural scientist, and his speculative nature found little appeal in post-revolutionary France, where science became increasingly empirical .
Lamarck received harsh criticism from the influential Georges Cuvier , who dismantled his theory in an obituary ( éloge ) of all things . On the one hand, Cuvier criticized Lamarck's speculative theory, which is only weakly based on empirical foundations, a point on which contemporary science historians largely agree with him. On the other hand, however, he drew - ignoring Lamarck's three causal three-step process, from a changed environment through habits to heredity - a picture of a theory in which the will or desires of organisms control evolution, which led to Lamarck being later often ascribed to vitalism .
Distorting representations like the one just mentioned, which are now classified as “caricature” or “pseudo-Lamarckism”, permanently shaped the public perception of Lamarck. He was a radical materialist and was even criticized for this by creationist representatives like William Kirby during his lifetime . Indeed, in his theory, which includes the origin of life through spontaneous generation, a creator does not play a role.
Even Charles Darwin did not think much of Lamarck. He had studied his books, but rarely mentioned them in official writings and referred to the books privately as "veritable rubbish". He couldn't quite understand the appreciation his friend Charles Lyell had for Lamarck. From today's perspective, however, it is assumed that Darwin was - directly or indirectly - more influenced by Lamarck than is traditionally ascribed to him. Darwin's Pangenesis theory also contains the idea of the “Lamarckian” inheritance of acquired properties. The principle of natural selection, which was so central to Darwin, was completely alien to Lamarck, because differences between individuals of a species played no role in his thinking.
From today's perspective, some historians of science criticize Lamarck's ahistorical portrayal in textbooks. Possibly influenced by the later debate between neo-marckists and neo-Darwinists, Lamarck is falsely portrayed as the adversary of Darwin and his theory is reduced to the example of the giraffe.
Neolamarckism
Lamarckism in today's sense, i.e. the concept of inheriting acquired traits, did not emerge until the end of the 19th century, when a serious alternative to this was proposed. The reason for this was August Weismann , who with his germplasm theory "cleaned up" Darwinism to a certain extent of all Lamarckian elements. The Weismann Barrier prevents any influence of somatic changes back on the genome. In Weismann's theory, natural selection is the only effective force; there are no “soft” inheritance mechanisms in it.
Sharp debates arose between the supporters of Weismann, who are known as “neo-Darwinists”, and the “neo-marckists”. One of the problems on the Darwinian side was to explain the regression of organs. The Lamarckists, on the other hand, found it difficult to provide experimental evidence for their theses and to reconcile their theory with Gregor Mendel's genetics, which had been rediscovered at the turn of the century .
Around 1900, Neolamarckism was therefore not the marginal phenomenon it is today, but a widely accepted position. Supporters of the inheritance of acquired traits included, among others, Edward Drinker Cope , Herbert Spencer and Ernst Haeckel . When Pierre de Coubertin resurrected the Olympic Games in 1894, he was shaped by the spirit of Neolamarckism. In his project des rebroncer la France he wanted to make the male population of France fit like the English through sport after the defeat in the Franco-Prussian War , in order to be able to defeat the German gymnasts . He assumed that fitness could be passed on and that each generation would be more productive than the previous one - if only they trained enough.
The dispute was ultimately not only conducted on a scientific, but also on a political level. At first, evolutionary standpoints could not be clearly assigned to ideological positions. This changed, however, at the beginning of the 1930s, when eugenic theories based on Darwin and Mendel gained in importance, especially in National Socialist Germany. Lamarckism was henceforth associated with "left", socialist positions. The National Socialists viewed it as a product of “liberal-Jewish-Bolshevik science”.
Paul Kammerer , who was himself exposed to anti-Semitic attacks by August Weismann , Fritz Lenz and Ludwig Plate , accused Weismann's supporters of demanding, with racist fanaticism, that only one race should emerge victorious from a selection process. In contrast, as a Lamarckist, he strives for an improvement in the welfare of all humanity. One of the things that made Lamarckism appealing to many people was the hope that improvements in the present can have a direct impact on the genome of future generations.
Until the 1920s, Lamarckism was one of the most important theories alongside Neo-Darwinism among Weismann's followers. However, there was no convincing experimental evidence, scandals such as the Paul Kammerer affair weakened the Lamarckist position, and finally it was possible to combine genetics with Darwinism. With the development of modern evolutionary synthesis , Lamarckism was finally scientifically obsolete.
In the Soviet Union, however, it survived for a while. The Soviet agronomist Trofim Denisovich Lyssenko advocated a modified form of Lamarckism during the reign of Joseph Stalin in the USSR and tried to prove the inheritance of acquired traits. At his instruction, considerable areas were planted with wheat, which were not climatically suitable for this. The resulting bad harvests exacerbated the poor food situation of the Russian population in a time of famine. The control of science practiced by politics is also known as Lyssenkoism . It was not until the mid-1950s (after the death of his sponsor Stalin) that Lyssenko's influence began to wane, and he was fired in 1962.
Experimental proof attempts
There have been various attempts by scientists to demonstrate Lamarckian inheritance mechanisms. An early example of this is Charles-Édouard Brown-Séquard , who attempted to show the inheritance of artificially inflicted epilepsy in guinea pigs. August Weismann also carried out experiments to show the non-existence of Lamarckism. He cut off the tails of mice in order to be able to observe fully developed tails in all subsequent generations. However, these experiments were criticized then as now, and even Weismann was aware of their inadequacy in falsifying Lamarckism. Lamarck had already emphasized the three-step process from changing nature through changing habits (e.g. use / non-use of organs) to heredity - even Lamarckists did not see wounds and external violence as influencing factors on inheritance.
More fundamental were the attempts by Paul Kammerer to prove the inheritance of acquired traits. With experiments and a. it was at times very well known in salamanders and midwife toads . However, his results could not be reproduced because only he could get the toads to reproduce in captivity. When toads manipulated with ink were finally found, Kammerer's scientific reputation was shattered and he committed suicide in 1926. It is still not clear whether Kammerer, who protested his innocence until his death, was guilty of fraud. There is now the consideration of whether Kammerer's experiments should be reevaluated on the basis of epigenetics .
The experimental evidence in favor of Lamarckism was therefore mostly weak since 1900, especially since there were mostly alternative explanations for the few results supporting Lamarckism. Moral-ideological reasons helped to keep the idea of inheritance of acquired traits alive for a long time.
A controversial thesis states that the CRISPR / Cas mechanism of inheritance of the immunity of some bacterial species against phages ( viruses ) by taking over their DNA into the bacterial genome is the first Lamarckian inheritance mechanism found.
literature
- Peter J. Bowler: Lamarckian Inheritance. In: Encyclopedia of Life Sciences . 2006
- Richard Burkhardt: The Spirit of System: Lamarck and Evolutionary Biology.
- Stephen Jay Gould : The structure of evolutionary theory. Belknap Press of Harvard University Press, Cambridge, Mass. 2002, ISBN 0-674-00613-5 .
- Ernst Mayr : Lamarck Revisited. In: Journal of the History of Biology. Volume 5, No. 1, 1972, pp. 55-94
- Alpheus Spring Packard : Lamarck, The Founder Of Evolution. His Life and Work. [1]
- Eliza Slavet: Freud's Lamarckism 'and the Politics of Racial Science. In: Journal of the History of Biology. Volume 41, No. 1, 2008, pp. 37-80
Web links
Individual evidence
- ↑ August Weismann : About inheritance. Fischer, Jena 1883
- ^ Jean-Baptiste de Lamarck : Philosophy zoologique, ou, Exposition des considérations relative à l'histoire naturelle des animaux. Paris 1809 (German translation by Arnold Lang : Jena 1876)
- ↑ Jean-Baptiste de Lamarck: Histoire naturelle des animaux sans vertèbres présentant les caractères généraux et particuliers de ces animaux, leur distribution, leurs genres, et la citation des principales espèces qui s'y rapportent: précédée d'une introduction offrant la détermination des caractères essentiels de l'animal, sa distinction du végétal et des autres corps naturels: enfin, l'exposition des principes fondamentaux de la zoologie . Paris 1815-1822
- ↑ Mayr, p. 61
- ↑ Mayr
- ↑ Burkhardt
- ↑ Gould
- ^ Gould, p. 177
- ↑ Burkhardt, p. 2
- ↑ Lamarck 1809, p. 69
- ↑ Wolfgang Lefèvre "Jean Baptiste Lamarck (1744–1829") (PDF; 81 kB)
- ^ Gould, p. 189
- ↑ Mayr, p. 86
- ^ Gould, p. 172
- ↑ Mayr, S57
- ↑ Burkhardt, p. 188
- ^ Letter to Joseph Dalton Hooker. In: Darwin Correspondence Project. University of Cambridge, November 11, 1844, accessed April 24, 2019 .
- ^ Gould, p. 196
- ^ Gould, p. 194
- ↑ Mayr, p. 90
- ^ M. Ghiselin: The Imaginary Lamarck: A Look at Bogus "History" in Schoolbooks. Archived copy ( Memento of February 12, 2008 in the Internet Archive )
- ^ Gould, p. 204
- ↑ RG Rinard: Neo-Lamarckism and Technique: Hans Spemann and the Development of Experimental Embryology. In: Journal of the History of Biology. No. 21, p. 95
- ^ Arnd Krüger : Neo-Olympism between nationalism and internationalism. In: Horst Ueberhorst (Ed.): History of physical exercises. Volume 3/1, Bartels & Wernitz, Berlin 1980, pp. 522-568.
- ↑ Slavet, p 43
- ↑ Slavet, p. 39
- ↑ Slavet, p 49
- ↑ AE Gaissinovitch and Mark B. Adams: The Origins of Soviet Genetics and the Struggle with Lamarckism, 1922-1929. In: Journal of the History of Biology. Volume 13, No. 1, 1980, pp. 1, 26.
- ↑ Slavet, p 48
- ^ Bowler, p. 2
- ^ Gould, p. 201
- ↑ Alexander O. Vargas: Did Paul Kammerer Discover Epigenetic Inheritance? A Modern Look at the Controversial Midwife Toad Experiments . In: Journal of Experimental Zoology B . tape 312 , no. 7 , 2009, p. 667-671 , doi : 10.1002 / jez.b.21319 , PMID 19731234 .
- ^ Bowler, p. 3
- ↑ EV Kooni, YI Wolf: Is evolution Darwinian or / and Lamarckian? In: Biology Direct . tape 4 , 2009, p. 42 , doi : 10.1186 / 1745-6150-4-42 .