Morgan, Thomas Hunt (1866–1945)

Citation metadata

Date: 2007
Encyclopedia of World Scientists, Rev. ed.
Publisher: Facts On File
Series: Facts on File Science Library
Document Type: Biography
Pages: 1
Content Level: (Level 5)

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About this Person
Born: September 25, 1866 in Lexington, Kentucky, United States
Died: December 04, 1945 in Pasadena, California, United States
Nationality: American
Other Names: The Twentieth Century Mendel
Full Text: 
Page 525

Morgan, Thomas Hunt (1866–1945)

American

Geneticist, Embryologist

Thomas Hunt Morgan's experiments on fruit flies led to important discoveries in what was then the fledgling science of genetics. Morgan established the chromosome theory of heredity and proved that genes (the basic units of heredity) are located in a linear array on chromosomes. Through his research on a mutant variety of fruit fly he also discovered sex-linked genes, and with his research team he devised the first chromosome map. His understanding of chromosome mutations allowed him to offer a genetic explanation for CHARLES ROBERT DARWIN's theory of natural selection. The students he influenced at both Columbia University and California Institute of Technology (Caltech) included many future pioneers in the field of genetics.

Morgan was born in Lexington, Kentucky, on September 25, 1866, to a prominent family. His father, Charlton Hunt Morgan, had been the American consul in Italy during the 1860s, where he had assisted Giuseppe Garibaldi in his movement to unify Italy. His uncle, John Hunt Morgan, had been a general in the Confederate Army, and his maternal great-grandfather was Francis Scott Key, the composer of the American national anthem.

Morgan graduated summa cum laude from the State College of Kentucky (now the University of Kentucky) in 1880 with a B.S. in zoology, then pursued graduate studies in embryology and morphology at the Johns Hopkins University in Baltimore, Maryland. Under the tutelage of W. K. Brooks, Morgan investigated the embryology of sea spiders in an attempt to classify them as either arachnids or crustaceans. He completed his doctoral work and was awarded a Ph.D. in 1890. He remained at Hopkins for an additional year on a Bruce Fellowship.

From 1891 until 1904 Morgan taught at Bryn Mawr College, outside Philadelphia. During his tenure there he applied experimental methods to embryology. His research concerning sea urchin eggs piqued his interest about the hereditary information carried by each cell and the chemical or physical processes that controlled the inheritance of this information. In 1903 he published Evolution and Adaptation, which posited that mutation (a concept first proposed by HUGO MARIE DE VRIES) introduced variation, an essential aspect of evolutionary theory, to a population.

In 1904 Morgan accepted a position as head of experimental zoology at Columbia University, where he investigated how an organism's sex was determined. The topic was hotly contested, as some scientists cited environmental factors as the cause of sex determination, and others concluded that inheritance was the key. In 1908 Morgan began to breed Drosophila melanogaster (the fruit fly) for laboratory work. The flies were ideal for research because their breeding cycle was a mere three days. In 1910 Morgan showed that the X chromosome was involved with sex inheritance. That same year he postulated that certain genes were connected to the X chromosome and were thus sex-linked. He reached this conclusion by studying a mutant variety of fly—one with white eyes instead of the typical red. After mating these white-eyed males with their red-eyed sisters, Hopkins found that all the offspring had red eyes. However, when he mated these red-eyed offspring, they in turn produced some white-eyed offspring. All of the white-eyed offspring were male, indicating that the genes for eye color were connected to sex-specific chromosomes. By 1911 he had identified five sex-linked genes. Over the next 11 years he devised a map indicating the relative positions of 2,000 genes on the fruit fly chromosomes.

Morgan left Columbia in 1927 to create a biology department at Caltech, in Pasadena, California. Instead of focusing solely on his fruit fly work, he strove to explore larger questions of development and evolution. He remained at Caltech until his death in 1945.

His research garnered many honors. In 1933 Morgan won the Nobel Prize in physiology or medicine. His treatise supplying genetic explanations for Darwin's theories, A Critique of the Theory of Evolution, received the Darwin Medal in 1924, and in 1939 Morgan was awarded the Copley Medal of the Royal Society. His findings expanded the field of genetics and helped influence the next wave of genetic research.

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Gale Document Number: GALE|CX4065100637