Gemmule (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. 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. The etymology of the word comes from the Greek words pan (a prefix meaning 'whole', 'encompassing') and genesis ('birth') or genos ('origin'). Pangenesis mirrored ideas originally formulated by Hippocrates and other pre-Darwinian scientists, but built off of new concepts such as cell theory, explaining cell development as beginning with gemmules which were specified to be necessary for the occurrence of new growths in an organism, both in initial development and regeneration. It also accounted for regeneration and the Lamarckian concept of the inheritance of acquired characteristics, as a body part altered by the environment would produce altered gemmules. This made Pangenesis popular among the neo-Lamarckian school of evolutionary thought. This hypothesis was made effectively obsolete after the 1900 rediscovery among biologists of Gregor Mendel's theory of the particulate nature of inheritance.The hypothesis of pangenesis is as old as the belief in the inheritance of acquired characters. 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, Maupertius, von Haller and Herbert Spencer.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. 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. 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. The etymology of the word comes from the Greek words pan (a prefix meaning 'whole', 'encompassing') and genesis ('birth') or genos ('origin'). Pangenesis mirrored ideas originally formulated by Hippocrates and other pre-Darwinian scientists, but built off of new concepts such as cell theory, explaining cell development as beginning with gemmules which were specified to be necessary for the occurrence of new growths in an organism, both in initial development and regeneration. It also accounted for regeneration and the Lamarckian concept of the inheritance of acquired characteristics, as a body part altered by the environment would produce altered gemmules. This made Pangenesis popular among the neo-Lamarckian school of evolutionary thought. This hypothesis was made effectively obsolete after the 1900 rediscovery among biologists of Gregor Mendel's theory of the particulate nature of inheritance. 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). Darwin wrote that Hippocrates' pangenesis was 'almost identical with mine—merely a change of terms—and an application of them to classes of facts necessarily unknown to the old philosopher.' Science historian Conway Zirkle wrote that: 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. He also stated that pangenesis was the only scientific explanation ever offered for this concept, developing from Hippocrates' belief that 'the semen was derived from the whole body.' In the 13th century, pangenesis was commonly accepted on the principle that semen was a refined version of food unused by the body, which eventually translated to 15th and 16th century widespread use of pangenetic principles in medical literature, especially in gynecology. Later pre-Darwinian important applications of the idea included hypotheses about the origin of the differentiation of races. A theory put forth by Pierre Louis Maupertuis in 1745 called for particles from both parents governing the attributes of the child, although some historians have called his remarks on the subject cursory and vague. In 1749, French naturalist Georges-Louis Leclerc, Comte de Buffon developed a hypothetical system of heredity much like Darwin's pangenesis, wherein 'organic molecules' were transferred to offspring during reproduction and stored in the body during development. Commenting on Buffon's views, Darwin stated, 'If Buffon had assumed that his organic molecules had been formed by each separate unit throughout the body, his view and mine would have been very closely similar.' In 1801, Erasmus Darwin advocated a hypothesis of pangenesis in the third edition of his book Zoonomia. In 1809, Jean-Baptiste Lamarck in his Philosophie Zoologique put forth evidence for the idea that characteristics acquired during the lifetime of an organism, either from effects of the environment or 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 first known writings on the topic of Lamarckian ideas as they related to inheritance are found in a notebook he opened in 1837, also entitled Zoonomia. Historian Johnathan Hodge states that the theory of pangenesis itself first appeared in Darwin's notebooks in 1841. In 1861, Irish physician Henry Freke developed a variant of pangenesis in his book Origin of Species by Means of Organic Affinity. Freke proposed that all life was developed from microscopic organic agents which he named granules, which existed as 'distinct species of organizing matter' and would develop into different biological structures. In 1864, four years before the publication of Variation, Herbert Spencer in his book Principles of Biology proposed a theory of 'physiological units' similar to Darwin's gemmules, which likewise were said to be related to specific body parts and responsible for the transmission of characteristics of those body parts to offspring. He also supported the Lamarckian idea of transmission of acquired characteristics.