Lamarckism

However, Darwin's book On the Origin of Species gave credence to the idea of heritable effects of use and disuse, as Lamarck had done, and his own concept of pangenesis similarly implied soft inheritance.

Later, Mendelian genetics supplanted the notion of inheritance of acquired traits, eventually leading to the development of the modern synthesis, and the general abandonment of Lamarckism in biology.

The inheritance of acquired characters had been accepted previously by Hippocrates, Aristotle, Galen, Roger Bacon, Jerome Cardan, Levinus Lemnius, John Ray, Michael Adanson, Jo.

[10] Erasmus Darwin's Zoonomia (c. 1795) suggested that warm-blooded animals develop from "one living filament... with the power of acquiring new parts" in response to stimuli, with each round of "improvements" being inherited by successive generations.

[12] Darwin subsequently set out his concept of pangenesis in the final chapter of his book The Variation of Animals and Plants Under Domestication (1868), which gave numerous examples to demonstrate what he thought was the inheritance of acquired characteristics.

Pangenesis, which he emphasised was a hypothesis, was based on the idea that somatic cells would, in response to environmental stimulation (use and disuse), throw off 'gemmules' or 'pangenes' which travelled around the body, though not necessarily in the bloodstream.

He saw evolution as comprising four laws:[16][17] In 1830, in an aside from his evolutionary framework, Lamarck briefly mentioned two traditional ideas in his discussion of heredity, in his day considered to be generally true.

As the evolutionary biologists and historians of science Conway Zirkle, Michael Ghiselin, and Stephen Jay Gould have pointed out, these ideas were not original to Lamarck.

On the other hand it is difficult to disprove Lamarck's idea experimentally, and it seems that Weismann's experiment fails to provide the evidence to deny the Lamarckian hypothesis, since it lacks a key factor, namely the willful exertion of the animal in overcoming environmental obstacles.

"[24] He argued that "the restriction of 'Lamarckism' to this relatively small and non-distinctive corner of Lamarck's thought must be labelled as more than a misnomer, and truly a discredit to the memory of a man and his much more comprehensive system.

[27][28] Also included were paleontologists like Edward Drinker Cope and Alpheus Hyatt, who observed that the fossil record showed orderly, almost linear, patterns of development that they felt were better explained by Lamarckian mechanisms than by natural selection.

[29] With the development of the modern synthesis of the theory of evolution, and a lack of evidence for a mechanism for acquiring and passing on new characteristics, or even their heritability, Lamarckism largely fell from favour.

Unlike neo-Darwinism, neo-Lamarckism is a loose grouping of largely heterodox theories and mechanisms that emerged after Lamarck's time, rather than a coherent body of theoretical work.

The idea that living things could to some degree choose the characteristics that would be inherited allowed them to be in charge of their own destiny as opposed to the Darwinian view, which placed them at the mercy of the environment.

[31] According to the historian of science Peter J. Bowler, writing in 2003: One of the most emotionally compelling arguments used by the neo-Lamarckians of the late nineteenth century was the claim that Darwinism was a mechanistic theory which reduced living things to puppets driven by heredity.

The British anthropologist Frederic Wood Jones and the South African paleontologist Robert Broom supported a neo-Lamarckian view of human evolution.

[97] George Gaylord Simpson in his book Tempo and Mode in Evolution (1944) claimed that experiments in heredity have failed to corroborate any Lamarckian process.

He would doubtless have been greatly astonished to learn that a belief in the inheritance of acquired characters is now labeled "Lamarckian," although he would almost certainly have felt flattered if evolution itself had been so designated.

[9]Peter Medawar wrote regarding Lamarckism, "very few professional biologists believe that anything of the kind occurs—or can occur—but the notion persists for a variety of nonscientific reasons."

Medawar stated there is no known mechanism by which an adaptation acquired in an individual's lifetime can be imprinted on the genome and Lamarckian inheritance is not valid unless it excludes the possibility of natural selection, but this has not been demonstrated in any experiment.

On the other hand, tens of thousands of experiments— reported in the journals and carefully checked and rechecked by geneticists throughout the world— have established the correctness of the gene-mutation theory beyond all reasonable doubt...

[104] Studies in the field of epigenetics, genetics and somatic hypermutation[105][106] have highlighted the possible inheritance of traits acquired by the previous generation.

[135] Haig has written that there is a "visceral attraction" to Lamarckian evolution from the public and some scientists, as it posits the world with a meaning, in which organisms can shape their own evolutionary destiny.

[136] Thomas Dickens and Qazi Rahman (2012) have argued that epigenetic mechanisms such as DNA methylation and histone modification are genetically inherited under the control of natural selection and do not challenge the modern synthesis.

[137] In 2015, Khursheed Iqbal and colleagues discovered that although "endocrine disruptors exert direct epigenetic effects in the exposed fetal germ cells, these are corrected by reprogramming events in the next generation.

This reverse transcription process supposedly enabled characteristics or bodily changes acquired during a lifetime to be written back into the DNA and passed on to subsequent generations.

[141][142] The mechanism was meant to explain why homologous DNA sequences from the VDJ gene regions of parent mice were found in their germ cells and seemed to persist in the offspring for a few generations.

[106][105][143] The historian of biology Peter J. Bowler noted in 1989 that other scientists had been unable to reproduce his results, and described the scientific consensus at the time:[138] There is no feedback of information from the proteins to the DNA, and hence no route by which characteristics acquired in the body can be passed on through the genes.

... [His] mechanism did not, in fact, violate the principles of molecular biology, but most biologists were suspicious of Steele's claims, and attempts to reproduce his results have failed.

[138]Bowler commented that "[Steele's] work was bitterly criticized at the time by biologists who doubted his experimental results and rejected his hypothetical mechanism as implausible.