Pangenesis

Pangenesis was Charles Darwin's hypothetical mechanism for heredity. He presented this 'provisional hypothesis' in his 1868 work The Variation of Animals and Plants under Domestication and felt that it brought 'together a multitude of facts which are at present left disconnected by any efficient cause'. The etymology of the word comes from the Greek words pan (a prefix meaning "whole", "encompassing") and genesis ("birth") or genos ("origin"). The hypothesis was eventually replaced by Mendel's laws of inheritance.

The pangenesis theory, similarly to [1]

Overview

Darwin's pangenesis theory was complex as he tried to explain the process of sexual reproduction, passing of traits and complex developmental phenomena, such as cellular regeneration.[2][3] His pangenesis theory was criticised for its Lamarckian premise that parents could pass on traits acquired in their lifetime. 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 scrawny) were not heritable.[4][5] Some Lamarckian principles, however, have not been entirely discounted and some of Darwin's pangenesis principles (in this regard) do relate to heritable aspects of phenotypic plasticity, while the status of gemmules has been firmly rejected. 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.[2][6][7]

Later elaboration

In his later work, sexual selection, he also stipulated that certain traits could be passed through organisms but would only develop depending on the sex of the organism in question.

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 in 1869 to 1871, he transfused the blood between dissimilar breeds of rabbits, and examined the features of their offspring [1]. He found no evidence of characters transmitted in the transfused blood (Bulmer 2003, pp. 116–118). Darwin challenged the validity of Galton's experiment, giving his reasons in an article published in 'Nature'[2] where he wrote: "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."

See also

References

  • Bulmer M. G. "Francis Galton: Pioneer of heredity and biometry" [3]

External links

  • The Variation of Animals and Plants Under DomesticationOn-line Facsimile Edition of from Electronic Scholarly Publishing
  • Variation under Domestication, From: Freeman, R. B. 1977. The Works of Charles Darwin: An Annotated Bibliographical Handlist. 2nd edn. Dawson: Folkstone, at DarwinOnline, with links to online versions of the 1st. edition, first and second issues, and the 2nd. edition.

References

  1. ^ Darwin, Charles (1868). The variation of animals and plants under domestication. London: John Murray.  
  2. ^ a b Geison, G. L. (1969). "Darwin and heredity: The evolution of his hypothesis of pangenesis". J Hist Med Allied Sci XXIV (4): 375–411.  
  3. ^ Jablonka, E.; Lamb, M. (2005). Evolution in four dimensions: Genetic, epigenetic, behavioural and symbolic. MIT Press.  
  4. ^  
  5. ^ Magner, Lois N. (2002). A History of the Life Sciences (Third ed.).  
  6. ^ West-Eberhard, M. J. "Toward a modern revival of Darwin's theory of evolutionary novelty". Philosophy of Science 75 (5): 899–908.  
  7. ^ Liu, Y. S.; Zhou, X. M.; Zhi, M. X.; Li, X. J.; Wan, Q. L. (2009). "Darwin's contributions to genetics". J Appl Genet 50 (3): 177–184.  
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