Pangenesis
Pangenesis was Charles Darwin's hypothetical mechanism for heredity, in which he proposed that each part of the body continually emitted its own type of small organic particles called gemmules that aggregated in the gonads, contributing heritable information to the gametes.
[1] He presented this 'provisional hypothesis' in his 1868 work The Variation of Animals and Plants Under Domestication, intending it to fill what he perceived as a major gap in evolutionary theory at the time.
Pangenesis was similar to ideas put forth by Hippocrates, Democritus and other pre-Darwinian scientists in proposing that the whole of parental organisms participate in heredity (thus the prefix pan).
It was endorsed by Hippocrates, Democritus, Galen, Clement of Alexandria, Lactantius, St. Isidore of Seville, Bartholomeus Anglicus, St. Albert the Great, St. Thomas of Aquinas, Peter of Crescentius, Paracelsus, Jerome Cardan, Levinus Lemnius, Venette, John Ray, Buffon, Bonnet, Maupertuis, von Haller and Herbert Spencer.
[4]Zirkle demonstrated that the idea of inheritance of acquired characteristics had become fully accepted by the 16th century and remained immensely popular through to the time of Lamarck's work, at which point it began to draw more criticism due to lack of hard evidence.
[9] In 1809, Jean-Baptiste Lamarck in his Philosophie Zoologique put forth evidence for the idea that characteristics acquired during the lifetime of an organism, from either environmental or behavioural effects, may be passed on to the offspring.
Charles Darwin first had significant contact with Lamarckism during his time at the University of Edinburgh Medical School in the late 1820s, both through Robert Edmond Grant, whom he assisted in research, and in Erasmus's journals.
Darwin's pangenesis theory attempted to explain the process of sexual reproduction, inheritance of traits, and complex developmental phenomena such as cellular regeneration in a unified mechanistic structure.
Responding to Fleming Jenkin's review of On the Origin of Species, he argued that pangenesis would permit the preservation of some favourable variations in a population so that they wouldn't die out through blending.
[2] Hugo de Vries characterized his own version of pangenesis theory in his 1889 book Intracellular Pangenesis with two propositions, of which he only accepted the first: The historian of science Janet Browne points out that while Spencer and Carl von Nägeli also put forth ideas for systems of inheritance involving gemmules, their version of gemmules differed from Darwin's in that it contained "a complete microscopic blueprint for an entire creature.
[4] Browne adds that Darwin believed specifically in gemmules from each body part because they might explain how environmental effects could be passed on as characteristics to offspring.
[4] For instance, an address by Huxley spurred on substantial work by Dr. James Ross in linking ideas found in Darwin's pangenesis to the germ theory of disease.
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.
[30] Darwin challenged the validity of Galton's experiment, giving his reasons in an article published in Nature where he wrote:[31] 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.
[3] 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.
[22] 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.
[41] 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.
