Thomas Hunt Morgan

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Thomas Hunt Morgan (September 25, 1866 – December 4, 1945)

evolutionary biologist, geneticist, embryologist, and science author who won the Nobel Prize in Physiology or Medicine in 1933 for discoveries elucidating the role that the chromosome plays in heredity.[3]

Morgan received his Ph.D. from Johns Hopkins University in zoology in 1890 and researched embryology during his tenure at Bryn Mawr. Following the rediscovery of Mendelian inheritance in 1900, Morgan began to study the genetic characteristics of the fruit fly Drosophila melanogaster. In his famous Fly Room at Columbia University's Schermerhorn Hall, Morgan demonstrated that genes are carried on chromosomes and are the mechanical basis of heredity. These discoveries formed the basis of the modern science of genetics.

During his distinguished career, Morgan wrote

22 books and 370 scientific papers.[2] As a result of his work, Drosophila became a major model organism in contemporary genetics. The Division of Biology which he established at the California Institute of Technology
has produced seven Nobel Prize winners.

Early life and education

Morgan was born in

Star Spangled Banner", and John Eager Howard, governor and senator from Maryland.[4]
Following the Civil War, the family fell on hard times with the temporary loss of civil and some property rights for those who aided the Confederacy. His father had difficulty finding work in politics and spent much of his time coordinating veterans' reunions.

Beginning at age 16 in the Preparatory Department, Morgan attended the State College of Kentucky (now the University of Kentucky). He focused on science; he particularly enjoyed natural history, and worked with the U.S. Geological Survey in his summers. He graduated as valedictorian in 1886 with a Bachelor of Science degree.[5] Following a summer at the Marine Biology School in Annisquam, Massachusetts, Morgan began graduate studies in zoology at the recently founded Johns Hopkins University. After two years of experimental work with morphologist William Keith Brooks and writing several publications, Morgan was eligible to receive a Master of Science from the State College of Kentucky in 1888. The college required two years of study at another institution and an examination by the college faculty. [citation needed] The college offered Morgan a full professorship; however, he chose to stay at Johns Hopkins and was awarded a relatively large fellowship to help him fund his studies.[citation needed]

Under Brooks, Morgan completed his thesis work on the embryology of

Bahamas and Europe to conduct further research.[6]

Every summer from 1910 to 1925, Morgan and his colleagues at the famous Fly Room at Columbia University moved their research program to the Marine Biological Laboratory. Aside from being an independent investigator at the MBL from 1890 to 1942, he became very involved in the governance of the institution, including serving as an MBL trustee from 1897 to 1945.[7]

Career and research

Bryn Mawr

In 1890, Morgan was appointed associate professor (and head of the biology department) at Johns Hopkins' sister school

sea acorns
, ascidian worms, and frogs.

In 1894 Morgan was granted a year's absence to conduct research in the laboratories of

ctenophore embryology. In Naples and through Loeb, he became familiar with the Entwicklungsmechanik (roughly, "developmental mechanics") school of experimental biology. It was a reaction to the vitalistic Naturphilosophie, which was extremely influential in 19th-century morphology. Morgan changed his work from traditional, largely descriptive morphology to experimental embryology that sought physical and chemical explanations for organismal development.[10]

At the time, there was considerable scientific debate over the question of how an embryo developed. Following

epigenetic and environmental factors in development; on this front Morgan showed that sea urchin eggs could be induced to divide without fertilization by adding magnesium chloride. Loeb continued this work and became well known for creating fatherless frogs using the method.[12]
[13]

When Morgan returned to Bryn Mawr in 1895, he was promoted to full professor. Morgan's main lines of experimental work involved regeneration and larval development; in each case, his goal was to distinguish internal and external causes to shed light on the Roux-Driesch debate. He wrote his first book, The Development of the Frog's Egg (1897). He began a series of studies on different organisms' ability to regenerate. He looked at grafting and regeneration in tadpoles, fish, and earthworms; in 1901 he published his research as Regeneration.

Beginning in 1900, Morgan started working on the problem of sex determination, which he had previously dismissed when Nettie Stevens discovered the impact of the Y chromosome on sex. He also continued to study the evolutionary problems that had been the focus of his earliest work.[14]

Columbia University

Morgan worked at Columbia University for 24 years, from 1904 until 1928 when he left for a position at the California Institute of Technology.

In 1904, his friend, Jofi Joseph died of tuberculosis, and he felt he ought to mourn her, though E. B. Wilson—still blazing the path for his younger friend—invited Morgan to join him at Columbia University. This move freed him to focus fully on experimental work.[15]

In a typical Drosophila genetics experiment, male and female flies with known phenotypes are put in a jar to mate; females must be virgins. Eggs are laid in porridge which the larvae feed on; when the life cycle is complete, the progeny are scored for the inheritance of the trait of interest.

When Morgan took the professorship in experimental zoology, he became increasingly focused on the mechanisms of heredity and evolution. He published Evolution and Adaptation (1903); like many biologists at the time, he saw evidence for biological evolution (as in the common descent of similar species) but rejected Darwin's proposed mechanism of natural selection acting on small, constantly produced variations.

Extensive work in

Garland Allen, he was also hindered by his views on taxonomy: he thought that species were entirely artificial creations that distorted the continuously variable range of real forms, while he held a "typological" view of larger taxa and could see no way that one such group could transform into another. But while Morgan was skeptical of natural selection for many years, his theories of heredity and variation were radically transformed through his conversion to Mendelism.[16]

In 1900 three scientists,

mutation theory
with his experimental heredity work. He was initially skeptical of Mendel's laws of heredity (as well as the related chromosomal theory of sex determination), which were being considered as a possible basis for natural selection.

Sex linked inheritance of the white eyed mutation.

Following

sex-linked, (2) the trait was probably carried on one of the sex chromosomes
, and (3) other genes were probably carried on specific chromosomes as well.

Morgan's illustration of crossing over, from his 1916 A Critique of the Theory of Evolution

Morgan and his students became more successful at finding mutant flies; they counted the mutant characteristics of thousands of fruit flies and studied their inheritance. As they accumulated multiple mutants, they combined them to study more complex inheritance patterns. The observation of a miniature-wing mutant, which was also on the sex chromosome but sometimes sorted independently to the white-eye mutation, led Morgan to the idea of genetic linkage and to hypothesize the phenomenon of crossing over. He relied on the discovery of Frans Alfons Janssens, a Belgian professor at the University of Leuven, who described the phenomenon in 1909 and had called it chiasmatypy. Morgan proposed that the amount of crossing over between linked genes differs and that crossover frequency might indicate the distance separating genes on the chromosome. The later English geneticist J. B. S. Haldane suggested that the unit of measurement for linkage be called the morgan. Morgan's student Alfred Sturtevant developed the first genetic map in 1913.

chromosome theory of inheritance. The map shows the relative positions of allelic characteristics on the second Drosophila chromosome. The distance between the genes (map units) is equal to the percentage of crossing-over events that occurs between different alleles.[19]

In 1915 Morgan, Sturtevant,

H. J. Muller wrote the seminal book The Mechanism of Mendelian Heredity.[20] Geneticist Curt Stern called the book "the fundamental textbook of the new genetics"[21] and C. H. Waddington noted that "Morgan's theory of the chromosome represents a great leap of imagination comparable with Galileo or Newton".[citation needed
]

In the following years, most biologists came to accept the

W. E. Castle pointed to contrary results in other organisms, suggesting that genes interact with each other, while Richard Goldschmidt and others thought there was no compelling reason to view genes as discrete units residing on chromosomes.[22]

Because of Morgan's dramatic success with Drosophila, many other labs throughout the world took up fruit fly genetics. Columbia became the center of an informal exchange network, through which promising mutant Drosophila strains were transferred from lab to lab; Drosophila became one of the first and for some time the most widely used, model organisms.[23] Morgan's group remained highly productive, but Morgan largely withdrew from doing fly work and gave his lab members considerable freedom in designing and carrying out their own experiments.

He returned to embryology and worked to encourage the spread of genetics research to other organisms and the spread of mechanistic experimental approach (Enwicklungsmechanik) to all biological fields.[24] After 1915, he also became a strong critic of the growing eugenics movement, which adopted genetic approaches in support of racist views of "improving" humanity.[25]

Morgan's fly-room at Columbia became world-famous, and he found it easy to attract funding and visiting academics. In 1927 after 25 years at Columbia, and nearing the age of retirement, he received an offer from George Ellery Hale to establish a school of biology in California.

Caltech

1931 drawing of Thomas Hunt Morgan

In 1928 Morgan joined the faculty of the California Institute of Technology where he remained until his retirement 14 years later in 1942.

Morgan moved to California to head the Division of Biology at the

Edward L. Tatum, Linus Pauling, Frits Went, Edward B. Lewis, and Sidney W. Byance with his reputation, Morgan held numerous prestigious positions in American science organizations. From 1927 to 1931 Morgan served as the President of the National Academy of Sciences; in 1930 he was the President of the American Association for the Advancement of Science; and in 1932 he chaired the Sixth International Congress of Genetics in Ithaca, New York. In 1933 Morgan was awarded the Nobel Prize in Physiology or Medicine; he had been nominated in 1919 and 1930 for the same work. As an acknowledgment of the group nature of his discovery, he gave his prize money to Bridges, Sturtevant, and his own children. Morgan declined to attend the awards ceremony in 1933, instead attending in 1934. The 1933 rediscovery of the giant polytene chromosomes in the salivary gland of Drosophila may have influenced his choice. Until that point, the lab's results had been inferred from phenotypic results, the visible polytene chromosome enabled them to confirm their results on a physical basis. Morgan's Nobel acceptance speech entitled "The Contribution of Genetics to Physiology and Medicine" downplayed the contribution genetics could make to medicine beyond genetic counseling. In 1939 he was awarded the Copley Medal
by the Royal Society.

He received two extensions of his contract at Caltech, but eventually retired in 1942, becoming a professor and chairman emeritus. George Beadle returned to Caltech to replace Morgan as chairman of the department in 1946. Although he had retired, Morgan kept offices across the road from the Division and continued laboratory work. In his retirement, he returned to the questions of sexual differentiation, regeneration, and embryology.

Death

Morgan had throughout his life suffered from a chronic

duodenal ulcer
. In 1945, at age 79, he experienced a severe heart attack and died from a ruptured artery.

Morgan and evolution

Morgan was interested in evolution throughout his life. He wrote his thesis on the phylogeny of sea spiders (

pycnogonids) and wrote four books about evolution. In Evolution and Adaptation (1903), he argued the anti-Darwinist position that selection could never produce wholly new species by acting on slight individual differences.[26] He rejected Darwin's theory of sexual selection[27] and the Neo-Lamarckian theory of the inheritance of acquired characters.[28] Morgan was not the only scientist attacking natural selection. The period 1875–1925 has been called 'The eclipse of Darwinism'.[29]
After discovering many small stable heritable mutations in Drosophila, Morgan gradually changed his mind. The relevance of mutations for evolution is that only characters that are inherited can have an effect on evolution. Since Morgan solved the problem of heredity (1915), he was in a unique position to examine critically Darwin's theory of natural selection.

In A Critique of the Theory of Evolution (1916), Morgan discussed questions such as: "Does selection play any role in evolution? How can selection produce anything new? Is selection no more than the elimination of the unfit? Is selection a creative force?" After eliminating some misunderstandings and explaining in detail the new science of Mendelian heredity and its chromosomal basis, Morgan concludes, "the evidence shows clearly that the characters of wild animals and plants, as well as those of domesticated races, are inherited both in the wild and in domesticated forms according to the Mendel's Law". "Evolution has taken place by the incorporation into the race of those mutations that are beneficial to the life and reproduction of the organism".[30] Injurious mutations have practically no chance of becoming established.[31] Far from rejecting evolution, as the title of his 1916 book may suggest, Morgan, laid the foundation of the science of genetics. He also laid the theoretical foundation for the mechanism of evolution: natural selection. Heredity was a central plank of Darwin's theory of natural selection, but Darwin could not provide a working theory of heredity. Darwinism could not progress without a correct theory of genetics. By creating that foundation, Morgan contributed to the neo-Darwinian synthesis, despite his criticism of Darwin at the beginning of his career. Much work on the Evolutionary Synthesis remained to be done.

Awards and honors

Morgan left an important legacy in genetics. Some of Morgan's students from Columbia and Caltech went on to win their own Nobel Prizes, including

George Wells Beadle and Hermann Joseph Muller. Nobel prize winner Eric Kandel has written of Morgan, "Much as Darwin's insights into the evolution of animal species first gave coherence to nineteenth-century biology as a descriptive science, Morgan's findings about genes and their location on chromosomes helped transform biology into an experimental science."[32]

Personal life

On June 4, 1904, Morgan married

polio research. Morgan was an atheist.[35][36][37][38]

See also

References

  1. ^ a b "Thomas Morgan". Nasonline.org. Retrieved 28 April 2019.
  2. ^
    S2CID 178714833
    .
  3. ^ a b "The Nobel Prize in Physiology or Medicine 1933". Nobel Web AB. Retrieved 2010-09-14.
  4. ^ a b Sturtevant (1959), p. 283.
  5. ^ Allen (1978), pp. 11–14, 24.
  6. ^ Allen, Thomas Hunt Morgan: The Man and His Science, pp. 46–51
  7. PMID 19276218
    .
  8. S2CID 161395714
    .
  9. ^ Allen, Thomas Hunt Morgan, pp. 50–53
  10. ^ Allen, Thomas Hunt Morgan, pp. 55–59, 72–80
  11. ^ Allen, Thomas Hunt Morgan, pp. 55–59, 80–82
  12. hdl:2027/hvd.32044107304297
    .
  13. ^ Loeb, Jacques (1913). Artificial parthenogenesis and fertilization. University of Chicago Press. jacques loeb sea urchin.
  14. ^ Allen, Thomas Hunt Morgan, pp. 84–96
  15. ^ Allen, Thomas Hunt Morgan, pp. 68–70
  16. ^ Allen, Thomas Hunt Morgan: The Man and His Science, pp. 105–116
  17. ^ a b Kohler, Lords of the Fly, pp. 37–43
  18. ^ Hamilton, Vivien (2016). "The Secrets of Life: Historian Luis Campos resurrects radium's role in early genetics research". Distillations. 2 (2): 44–45. Retrieved 22 March 2018.
  19. ISBN 978-0-07-325839-3
    .
  20. ^ Morgan, Thomas Hunt; Alfred H. Sturtevant, H. J. Muller and C. B. Bridges (1915). The Mechanism of Mendelian Heredity. New York: Henry Holt.{{cite book}}: CS1 maint: multiple names: authors list (link)
  21. ISSN 0011-5266
    .
  22. ^ Allen, Thomas Hunt Morgan, pp. 208–213, 257–278. Quotation from p. 213.
  23. ^ Kohler, Lords of the Fly, chapter 5
  24. ^ Allen, Thomas Hunt Morgan, pp. 214–215, 285
  25. ^ Allen, Thomas Hunt Morgan, pp. 227–234
  26. ISBN 9780674031753
    .
  27. ^ "I think we shall be justified in rejecting it as an explanation of the secondary sexual differences amongst animals", pp. 220–221, chapter VI, Evolution and Adaptation, 1903.
  28. ^ Chapter VII of Evolution and Adaptation, 1903.
  29. ^ Bowler, Peter (2003). Evolution. The History of an Idea. University of California Press. chapter 7.
  30. ^ A Critique of the Theory of Evolution, Princeton University Press, 1916, pp. 193–194
  31. ^ A Critique of the Theory of Evolution, p. 189.
  32. ^ Kandel, Eric. 1999. "Genes, Chromosomes, and the Origins of Modern Biology", Columbia Magazine
  33. ^ "APS Member History". search.amphilsoc.org. Retrieved 2023-11-02.
  34. ^ "Thomas Hunt Morgan". American Academy of Arts & Sciences. 2023-02-09. Retrieved 2023-11-02.
  35. ISBN 9780156031790
    . The Nobel Prize-winning geneticist and stringent atheist Thomas Hunt Morgan was developing the chromosome theory of heredity by examining his swarm of mutated Drosophila (fruit flies) through a jeweler's loupe.
  36. ^ "Morgan's passion for experimentation was symptomatic of his general skepticism and his distaste for speculation. He believed only what could be proven. He was said to be an atheist, and I have always believed that he was. Everything I knew about him—his skepticism, his honesty—was consistent with disbelief in the supernatural." Norman H. Horowitz, T. H. Morgan at Caltech: A Reminiscence, Genetics, Vol. 149, 1629–1632, August 1998.
  37. ^ Judith R. Goodstein. "The Thomas Hunt Morgan Era in Biology" (PDF). Calteches.library.caltech.edu. Archived from the original (PDF) on 22 August 2016. Retrieved 28 April 2019.
  38. PMID 9691024. Archived from the original
    on 5 April 2016. Retrieved 6 February 2017.

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