Editing Pangenesis (section)

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=== Galton's experiments on rabbits ===
Darwin's half-cousin [[Francis Galton]] conducted wide-ranging inquiries into heredity which led him to refute Charles Darwin's hypothetical theory of pangenesis. In consultation with Darwin, he set out to see if gemmules were transported in the blood. In a long series of experiments from 1869 to 1871, he transfused the blood between dissimilar breeds of rabbits, and examined the features of their offspring. He found no evidence of characters transmitted in the transfused blood.<ref>{{cite book |last=Bulmer |first=Michael G. |title=Francis Galton : pioneer of heredity and biometry |publisher=Johns Hopkins University Press |publication-place=Baltimore, Md. |date=2003 |isbn=978-0-8018-8140-4 |oclc=559350911 |pages=116–118}}</ref>

[[Francis Galton|Galton]] was troubled because he began the work in good faith, intending to prove Darwin right, and having praised pangenesis in ''Hereditary Genius'' in 1869. Cautiously, he criticized his cousin's theory, although qualifying his remarks by saying that Darwin's gemmules, which he called "pangenes", might be temporary inhabitants of the blood that his experiments had failed to pick up.{{sfn|Browne|2002|p=291–292}}

Darwin challenged the validity of Galton's experiment, giving his reasons in an article published in ''Nature'' where he wrote:<ref name=Darwin1871>{{cite journal |author=Darwin, Charles R. |author-link=Charles Darwin |date=27 April 1871 |url=http://darwin-online.org.uk/content/frameset?itemID=F1751&viewtype=side&pageseq=1 |title=Pangenesis |journal=Nature |volume=3 |issue=78 |pages=502–503 |doi=10.1038/003502a0 |bibcode=1871Natur...3..502D |doi-access=free }}</ref>

{{blockquote |Now, in the chapter on Pangenesis in my ''Variation of Animals and Plants under Domestication,'' I have not said one word about the blood, or about any fluid proper to any circulating system. It is, indeed, obvious that the presence of gemmules in the blood can form no necessary part of my hypothesis; for I refer in illustration of it to the lowest animals, such as the Protozoa, which do not possess blood or any vessels; and I refer to plants in which the fluid, when present in the vessels, cannot be considered as true blood." He goes on to admit: "Nevertheless, when I first heard of Mr. Galton's experiments, I did not sufficiently reflect on the subject, and saw not the difficulty of believing in the presence of gemmules in the blood.<ref name=Darwin1871/>}}

After the circulation of Galton's results, the perception of pangenesis quickly changed to severe skepticism if not outright disbelief.<ref name=":4"/>

=== Weismann ===
[[File:Weismann's Germ Plasm.svg |thumb |[[August Weismann]]'s [[germ plasm]] theory. The hereditary material, the germ plasm, is confined to the gonads. Somatic cells (of the body) develop afresh in each generation from the germ plasm. The implied [[Weismann barrier]] between the germ line and the soma prevents Lamarckian inheritance. |270x270px]]

[[August Weismann]]'s idea, set out in his 1892 book ''Das Keimplasma: eine Theorie der Vererbung'' (The Germ Plasm: a Theory of Inheritance),<ref>{{cite book |url=http://www.deutschestextarchiv.de/book/show/weismann_keimplasma_1892 |title=Das Keimplasma: eine Theorie der Vererbung |author=Weismann, August |date=1892 |publisher=Fischer |location=Jena |trans-title=The Germ Plasm: A theory of inheritance}}</ref> was that the hereditary material, which he called the [[germ plasm]], and the rest of the body (the [[Somatic (biology)|soma]]) had a one-way relationship: the germ-plasm formed the body, but the body did not influence the germ-plasm, except indirectly in its participation in a population subject to natural selection. This distinction is commonly referred to as the [[Weismann barrier|Weismann Barrier]]. If correct, this made Darwin's pangenesis wrong and Lamarckian inheritance impossible. His experiment on mice, cutting off their tails and showing that their offspring had normal tails across multiple generations, was proposed as a proof of the non-existence of Lamarckian inheritance, although Peter Gauthier has argued that [[Weismann's experiment]] showed only that injury did not affect the germ plasm and neglected to test the effect of Lamarckian use and disuse.<ref>{{cite journal |last=Gauthier |first=Peter |date=March–May 1990 |title=Does Weismann's Experiment Constitute a Refutation of the Lamarckian Hypothesis? |journal=BIOS |volume=61 |pages=6–8 |jstor=4608123 |number=1/2}}</ref> Weismann argued strongly and dogmatically for Darwinism and against neo-Lamarckism, polarising opinions among other scientists.<ref name=":6">{{Cite book |title=Neo-Lamarckism and the evolution controversy in France, 1870-1920 |author=Persell, Stuart Michael |date=1999 |publisher=Edwin Mellen Press |isbn=978-0773482753 |location=Lewiston, NY |oclc=40193707}}</ref> This increased anti-Darwinian feeling, contributing to [[Eclipse of Darwinism|its eclipse]].<ref>{{cite book |title=Evolution: The History of an Idea |last=Bowler |first=Peter J. |publisher=[[University of California Press]] |year=2003 |isbn=978-0-520-23693-6 |edition=3rd completely rev. and expanded |location=Berkeley, CA |pages=[https://archive.org/details/evolutionhistory0000bowl_n7y8/page/253 253–256] |author-link=Peter J. Bowler |url=https://archive.org/details/evolutionhistory0000bowl_n7y8/page/253}}</ref><ref>{{cite book |title=Evolution: The History of an Idea |last=Bowler |first=Peter J. |publisher=[[University of California Press]] |year=1989 |isbn=978-0-520-06386-0 |edition=2nd revised |location=Berkeley, CA |pages=[https://archive.org/details/evolutionhistory0000bowl/page/247 247–253, 257] |author-link=Peter J. Bowler |url=https://archive.org/details/evolutionhistory0000bowl/page/247}}</ref>

=== After pangenesis ===

Darwin's pangenesis theory was widely criticised, in part for its [[Lamarckism|Lamarckian]] premise that parents could [[inheritance of acquired characters|pass on traits acquired]] in their lifetime.<ref>{{Cite journal |last1=Liu |first1=Yongsheng |last2=Li |first2=Xiuju |date=2014-09-23 |title=Has Darwin's Pangenesis Been Rediscovered? |journal=BioScience |language=en |volume=64 |issue=11 |pages=1037–1041 |doi=10.1093/biosci/biu151 |issn=0006-3568 |doi-access=free}}</ref> Conversely, the neo-Lamarckians of the time seized upon pangenesis as evidence to support their case.<ref name=":6"/> Italian Botanist Federico Delpino's objection that gemmules' ability to self-divide is contrary to their supposedly innate nature gained considerable traction; however, Darwin was dismissive of this criticism, remarking that the particulate agents of smallpox and scarlet fever seem to have such characteristics.<ref name=":5"/> Lamarckism fell from favour after [[August Weismann]]'s research in the 1880s indicated that changes from use (such as lifting weights to increase muscle mass) and disuse (such as being lazy and becoming weak) were not heritable.<ref name="ImaginaryLamarck">{{Cite book |url=http://www.textbookleague.org/ |archive-url=https://web.archive.org/web/20000115220615/http://www.textbookleague.org/ |url-status=usurped |archive-date=January 15, 2000 |title=The Textbook Letter |last=Ghiselin |first=Michael T. |publisher=The Textbook League |date=September–October 1994 |contribution=Nonsense in schoolbooks: 'The Imaginary Lamarck' |author-link=Michael Ghiselin |access-date=2008-01-23 |contribution-url=http://www.textbookleague.org/54marck.htm}}</ref><ref>{{cite book |url=https://books.google.com/books?id=YKJ6gVYbrGwC |title=A History of the Life Sciences |last=Magner |first=Lois N. |publisher=[[Marcel Dekker]], [[CRC Press]] |year=2002 |isbn=978-0-203-91100-6 |edition=Third}}</ref> However, some scientists continued to voice their support in spite of Galton's and Weismann's results: notably, in 1900 Karl Pearson wrote that pangenesis "is no more disproved by the statement that 'gemmules have not been found in the blood,' than the atomic theory is disproved by the fact that no atoms have been found in the air."<ref>{{Cite book |url=https://books.google.com/books?id=PSwRAwAAQBAJ&q=The+Grammar+of+Science&pg=PA1 |title=The Grammar of Science |last=Pearson |first=Karl |publisher=Adam and Charles Black |year=1900 |isbn=9785877362529 |location=London |pages=335 |language=en}}</ref> Finally, the rediscovery of Mendel's Laws of Inheritance in 1900 led to pangenesis being fully set aside.<ref>{{cite book |last1=de Beer |first1=Gavin |title=Charles Darwin: A Scientific Biography |date=1965 |publisher=Doubleday & Company |location=Garden City, NY |page=206}}</ref> Julian Huxley has observed that the later discovery of [[chromosome]]s and the research of [[T. H. Morgan]] also made pangenesis untenable.<ref>{{Cite book |title=Heredity East and West: Lysenko and World Science |last=Huxley |first=Julian |publisher=Henry Schuman |year=1949 |location=New York |pages=11, 141}}</ref>

Some of Darwin's pangenesis principles do relate to heritable aspects of [[phenotypic plasticity]], although the status of gemmules as a distinct class of organic particles has been firmly rejected. However, starting in the 1950s, many research groups in revisiting Galton's experiments found that heritable characteristics could indeed arise in rabbits and chickens following DNA injection or blood transfusion.<ref name=":3">{{Cite journal |last=Liu |first=Yongsheng |date=2008 |title=A new perspective on Darwin's Pangenesis |journal=Biological Reviews |volume=83 |issue=2 |pages=141–149 |doi=10.1111/j.1469-185x.2008.00036.x |pmid=18429766 |s2cid=39953275}}</ref> This type of research originated in the Soviet Union in the late 1940s in the work of Sopikov and others, and was later corroborated by researchers in Switzerland as it was being further developed by the Soviet scientists.<ref name=":8">{{Cite journal |last=Kosin, I. L. and Masaru Kato |date=1963 |title=A failure to induce heritable changes in four generations of the White Leghorn chicken by inter- and intra-specific blood transfusion |url=http://lysvav.narod.ru/VH/Kosin_Kato.pdf |journal=Genetics Research Cambridge |volume=4 |issue=2 |pages=221–239 |doi=10.1017/S0016672300003578 |doi-access=free}}</ref><ref name=":4"/> Notably, this work was supported in the USSR in part due to its conformation with the ideas of [[Trofim Lysenko]], who espoused a version of neo-Lamarckism as part of [[Lysenkoism]].<ref name=":8"/> Further research of this heritability of acquired characteristics developed into, in part, the modern field of [[epigenetics]]. Darwin himself had noted that "the existence of free gemmules is a gratuitous assumption"; by some accounts in modern interpretation, gemmules may be considered a prescient mix of DNA, RNA, proteins, prions, and other mobile elements that are heritable in a non-Mendelian manner at the molecular level.<ref name="Geison69"/><ref name="West=Eberhard08">{{cite journal |last1=West-Eberhard |first1=M. J. |year=2008 |title=Toward a modern revival of Darwin's theory of evolutionary novelty |jstor=10.1086/594533 |journal=Philosophy of Science |volume=75 |issue=5 |pages=899–908 |doi=10.1086/594533 |citeseerx=10.1.1.456.9407 |s2cid=3850453 }}</ref><ref name="Liu09">{{cite journal |last1=Liu |first1=Y. S. |last2=Zhou |first2=X. M. |last3=Zhi |first3=M. X. |last4=Li |first4=X. J. |last5=Wan |first5=Q. L. |year=2009 |title=Darwin's contributions to genetics |url=http://jay.up.poznan.pl/JAG/pdfy/2009_Volume_50/2009_Volume_50_3-177-184.pdf |url-status=dead |journal=J Appl Genetics |volume=50 |issue=3 |pages=177–184 |doi=10.1007/BF03195671 |pmid=19638672 |s2cid=19919317 |archive-url=https://web.archive.org/web/20120330163705/http://jay.up.poznan.pl/JAG/pdfy/2009_Volume_50/2009_Volume_50_3-177-184.pdf |archive-date=2012-03-30}}</ref> Liu points out that Darwin's ideas about gemmules replicating outside of the body are predictive of ''in vitro'' gene replication used, for instance, in [[Polymerase chain reaction|PCR]].<ref name=":4"/>