Thomas Hunt Morgan (September 25, 1866 – December 4, 1945) was an American evolutionary biologist, geneticist, and embryologist. In 1933, he won the Nobel Prize in Physiology or Medicine for discoveries on the role of chromosomes in heredity.
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. 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.
Morgan was born in Lexington, Kentucky, to Charlton Hunt Morgan and Ellen Key Howard Morgan. Part of a line of Southern plantation and slave owners on his father's side, Morgan was a nephew of Confederate General John Hunt Morgan; his great-grandfather John Wesley Hunt had been one of the first millionaires west of the Allegheny Mountains. Through his mother, he was the great-grandson of Francis Scott Key, the author of the "Star Spangled Banner", and John Eager Howard, governor and senator from Maryland. 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. 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. 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.
Under Brooks, Morgan completed his thesis work on the embryology of sea spiders—collected during the summers of 1889 and 1890 at the Marine Biological Laboratory in Woods Hole, Massachusetts—to determine their phylogenetic relationship with other arthropods. He concluded that concerning embryology, they were more closely related to spiders than crustaceans. Based on the publication of this work, Morgan was awarded his Ph.D. from Johns Hopkins in 1890 and was also awarded the Bruce Fellowship in Research. He used the fellowship to travel to Jamaica, the Bahamas and Europe to conduct further research.
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.
In 1890, Morgan was appointed associate professor (and head of the biology department) at Johns Hopkins' sister school Bryn Mawr College, replacing his colleague Edmund Beecher Wilson. Morgan taught all morphology-related courses, while the other member of the department, Jacques Loeb, taught the physiological courses. Although Loeb stayed for only one year, it was the beginning of their lifelong friendship. Morgan lectured in biology five days a week, giving two lectures a day. He frequently included his recent research in his lectures. Although an enthusiastic teacher, he was most interested in research in the laboratory. During the first few years at Bryn Mawr, he produced descriptive studies of sea acorns, ascidian worms, and frogs. Morgan co-authored an 1894 paper on the division of the egg of Rana temporaria with Japanese Bryn Mawr student Ume Tsuda; this is considered to be the first scientific paper written in English by a Japanese woman.
In 1894 Morgan was granted a year's absence to conduct research in the laboratories of Stazione Zoologica in Naples, where Wilson had worked two years earlier. There he worked with German biologist Hans Driesch, whose research in the experimental study of development piqued Morgan's interest. Among other projects that year, Morgan completed an experimental study 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.
At the time, there was considerable scientific debate over the question of how an embryo developed. Following Wilhelm Roux's mosaic theory of development, some believed that hereditary material was divided among embryonic cells, which were predestined to form particular parts of a mature organism. Driesch and others thought that development was due to epigenetic factors, where interactions between the protoplasm and the nucleus of the egg and the environment could affect development. Morgan was in the latter camp; his work with Driesch demonstrated that blastomeres isolated from sea urchin and ctenophore eggs could develop into complete larvae, contrary to the predictions (and experimental evidence) of Roux's supporters. A related debate involved the role of 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.
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.
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.
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.