Herbert Spencer Jennings (1868-1947, APS 1907) was a microbiologist, zoologist and geneticist. In his critical monograph Contributions to the Study of the Behavior of Lower Organisms (1904) Jennings challenged the theory physicochemical tropisms in animals championed by Jacques Loeb (1859-1924, APS 1899), and brought single-celled organisms into the realm of psychology. He also helped to found the field of mathematical genetics by systematically applying principles of Mendelian theory to his calculations of expectable ratios of the traits in various types of inheritance. Jennings's most important contribution to genetics was his investigation of the questions of variation and evolution that confirmed the gradual but persistent progress of the latter by the accrual of very slight alterations.

Jennings was born on April 8, 1868, the son of physician George Nelson Jennings and Olive Taft Jenks, in Tonica, Illinois. He learned to read at a very early age, by delving into his father's extensive home library. From 1874-1879 the family lived in various localities in California, before returning to Tonica, Illinois, where Jennings attended a public high school. After high school, he studied at the Illinois Normal School near Bloomington (now Illinois State University) in 1887-88, then briefly taught in rural schools near his home in Tonica. At the age of twenty-one in 1889 without a degree, Jennings served as assistant professor of botany and horticulture at the Agricultural and Mechanical College of Texas (later Texas A & M University).

In 1890 Jennings matriculated at the University of Michigan, where he studied with the young zoologist and ichthyologist Jacob Reighard. He graduated with a B.S. in 1893. After a year of graduate study at Michigan, Jennings moved on to Harvard to study with Reighard's mentor Edward Laurens Mark at the Zoological Laboratory. He received an M.A. from Harvard in 1895 and a Ph.D. in 1896. His thesis was on the embryology of a rotifer. As a graduate student, Jennings was influenced by Charles Benedict Davenport (1866-1944, APS 1907), then a Harvard instructor, to shift his interests from descriptive to experimental biology. After completing his doctorate, Jennings was awarded the Parker traveling fellowship, which allowed him during the winter of 1896-97 to study the response of the Paramecium to stimuli with pioneering researcher on protozoan behavior Max Verworn at the University of Jena. In the spring of 1897 Jennings worked at the Naples Zoological Laboratory. Returning home that summer, he held several one-year appointments as professor of botany at the Montana State Agricultural and Mechanical College (1897-98) and as instructor in zoology at Dartmouth (1898-99) to replace a professor on leave. Also in 1898 Jennings wed Mary Louise Burridge, an artist and a son born to them later that year.

In 1899 Jennings became a zoology instructor at the University of Michigan, progressing to the rank of assistant professor in 1901. Also, in 1901 he coauthored a textbook with Reighard, entitled the Anatomy of the Cat. During his summers at the University of Michigan, Jennings continued to serve under Reighard's supervision as an assistant with the Michigan lake surveys. In 1902 he was appointed program director for the U.S. Fish Commission Biological Survey of the Great Lakes.

In 1903 Jennings became assistant professor of zoology at the University of Pennsylvania and was allowed a one-year leave to return to the Naples Zoological Laboratory, funded by a grant from the Carnegie Institution. He published the results of his research the following year as Contributions to the Study of the Behavior of Lower Organisms (1904). In 1906 Jennings moved on to Johns Hopkins University to become professor of experimental zoology. Here he was assigned light teaching duties and provided with a laboratory. In 1910 he was promoted to become Henry Walters Professor of Zoology and directed the zoological laboratory until his retirement in 1938.

Even before his post-doctoral studies, Jennings pursued experimental research on the behavior of primitive animals and their reactions to stimuli. Of his many published papers, Jennings's study of "The Psychology of a Protozoan" (1899) sparked the strongest reaction. He had become greatly interested in the complex behavior of these single-celled microorganisms, which he attributed to their entire structure. These views drew fire from University of Chicago biologist Jacques Loeb, who maintained the reactions of all life forms could ultimately be explained as physical or chemical reactions [i.e. tropisms]. However, at a scientific meeting in 1900 Jennings provided experimental demonstrations to prove the validity of his theory, and obtained the agreement of Loeb.

In 1900 Jennings was one of the many biologists inspired to study genetics by the rediscovery of Gregor Mendel's work on inheritance in plants. In his laboratory at Johns Hopkins he began to study the genetics and evolution of two species of single-celled organisms, the Paramecium and Difflugia. His goal was to discover the origin of hereditary variations in organisms, whose reproduction is primarily asexual. Jennings based his research on the characteristics of individual organisms (aggregating these results statistically, rather than studying them as groups). He discovered that the progeny of the individual organisms were identical with the "parent" organisms. Further studies by Jennings's graduate students showed that the same is true of multicellular organisms, reproducing by asexual means. Systematically applying Mendelian theory to his samples, he helped to found the field of mathematical genetics by calculating the expectable ratios of traits in various types of inheritance. Jennings's greatest contriubutions to genetics related to questions of variation and evolution. From 1908 to 1916 Jennings and his students published a number of papers, discussing the constancy and variability of traits in protozoan lines of inheritance. He demonstrated that within a given species there are a number of particular strains whose traits endure for many generations. However, he also noticed the spontaneous development of very slight, but persistent variations. The net effect of his work was to modify the theory of mutations, since the alterations he observed were so slight that they suggested evolution proceeded gradually by means of very small (rather than abrupt) changes. A contemporary university publication offered a somewhat exaggerated description of Jennings as the first scientific researcher "to actually see and control the process of evolution among living things."

After Jennings's appointment as Director of Johns Hopkins zoological laboratory, he had less time to spend on his own research, but continued to supervise the work of graduate students. He also produced an important series of writings that popularized genetics and discussed the philosophical implications of the new methods and findings of experimental biology. His popular books, that included Life and Death: Heredity and Evolution in Unicellular Organisms (1920), Prometheus; or, Biology and the Advancement of Man (1925), The Biological Basis of Human Nature (1930) and The Universe and Life (1933) focused on the central finding of his lifework that biological processes are identical across the animal kingdom. In 1935 he also authored a textbook entitled Genetics.

In 1938 his wife Mary died, shortly after Jennings's retirement from Johns Hopkins, and the following spring he accepted a position as visiting professor at the University of California at Los Angeles. There at the age of seventy he resumed his research on the Paramecium, about which he published several new papers. In 1939 he married Lulu Plant Jennings, his brother's widow.

Throughout his career Jennings held memberships and offices in many scientific societies and learned organizations. He was elected to the American Philosophical Society in 1907. He was also a member of the American Zoological Society (President, 1908-09), the Philadelphia Academy of Natural Sciences, the American Society of Naturalists (1910-11) and a fellow of the American Academy of Arts and Sciences (in 1914). Internationally, Jennings was an honorary fellow of the Royal Microscopical Society in Great Britain, a member of the Royal Society of Edinburgh, a member of the Société de Biologie de Paris and a corresponding member of the Russian Academy of Science.

In addition to his many scholarly and popular books on biology and genetics, Jennings published numerous papers in zoological and physiological journals. He was also the Associate Editor of the Journal of Experimental Zoology and Genetics and of the Biological Bulletin.

Jennings spent his final years in Los Angeles, California. He died in Santa Monica, California on April 14, 1947.

A diversified collection of great size. Includes correspondence, miscellaneous papers, diaries, manuscripts (many unpublished), notebooks, lecture notes, syllabi of courses taught by Jennings at Johns Hopkins University, scrapbooks, memorabilia, etc. Correspondents in the Jennings papers include: T. T. Chen (reserarch assistant), Samuel W. Geiser (graduate student), Arthur O. Lovejoy (colleague), Ruth Stocking Lynch (graduate student and research assistant), Samuel Ottmar Mast (graduate student and colleague), and Tracy M. Sonneborn (graduate student and colleague).

The papers 60 boxes, 30 linear feet are divided into seven series. Series I. Correspondence, 1992-1946, 16 boxes, 8 lin. ft.; Series II. Works by Jennings, 1890-1947, 15 boxes, 7.5 lin. ft.; Series III. Personal, 1886-1947, 2 boxes, 1 lin. ft.; Series IV. Graphics, 1897-1936, 1 box, 0.5 lin. ft.; Series V. Diaries and Notebooks, 1855-1942, 20 boxes, 10 lin. ft.; Series VI. Scrapbooks, 1921-1937, 7 boxes, 3.5 lin. ft.; Series VII. Photographs.

Arrangement is for the Reader Copies.

Provenance

Presented by Mrs. Vernon Lynch, Burridge Jennings, Carolyn Jennings, S. W. Geiser, and Tracy M. Sonneborn, 1947-1977. See in-house shelf for additional accession numbers and dates.

Other finding aids

The printed version of Bentley Glass' A Guide to the Genetics Collections of the American Philosophical Society contains another biography of Jennings and a further description of the Jennings Papers.

Naval History Note

The Jennings Papers contain at least one item which may be of interest to naval historians:

Navy Department Intelligence Office, 11th Naval District. Letter to Herbert S. Jennings. 1945 February 26. Asking for information on his foreign residence. 1 page.

Physiology, Biochemistry, and Biophysics Note

Scholars of physiology, biochemistry, or biophysics may find the following items of interest:

Genetics Note

This collection contains materials which relate to the history of genetics.

• Autobiographies.
• Certificates.
• Commonplace books.
• Diplomas.
• Lectures.
• Notebooks.
• Photoprints.

• Zoologists -- United States.

• Alexander, Jerome, 1876-1959
• Aydelotte, Frank, 1880-1956
• Blumer, Herbert, 1900-1987
• Brennemann, Joseph, 1872-1944
• Burbank, Luther, 1849-1926
• Calkins, Gary N. (Gary Nathan)
• Cattell, James McKeen, 1860-1944
• Chen, Tze-tuan
• Conklin, Edwin Grant, 1863-1952
• Cowdry, E. V. (Edmund Vincent), 1888-1975
• Davenport, Charles Benedict, 1866-1944
• Fisher, Irving, 1867-1947
• Geiser, Samuel Wood, 1890-1983
• Harrison, Ross G. (Ross Granville), 1870-1959
• Jennings, H. S. (Herbert Spencer), 1868-1947
• Kellogg, Vernon L. (Vernon Lyman), 1867-1937
• Korzybski, Alfred, 1879-1950
• Lillie, Frank Rattray, 1870-1947
• Mast, Samuel Ottmar, 1871-1947
• Metcalf, Maynard M. (Maynard Mayo), 1868-1940
• Metz, Carl W., 1889-1975
• Muller, H. J. (Hermann Joseph), 1890-1967
• Osterud, Hjalmar Laurits
• Pearl, Raymond, 1879-1940
• Pomeroy, Fred Elmer
• Raffel, Daniel
• Shull, George Harrison, 1874-1954
• Sonneborn, T. M. (Tracy Morton), 1905-1981
• Vavilov, N. I. (Nikolai Ivanov
• Watson, John B. (John Broadus), 1878-1958
• Whitney, Leon Fradley (1894-1973)
• Wilson, Edwin Bidwell, 1879-1964
• Yerkes, Robert Mearns, 1876-1956

• Animal behavior.
• Biology.
• Biometry.
• Correlation (Statistics)
• Emigration and immigration law -- United States.
• Eugenics.
• Evolution.
• Genetics.
• Heredity.
• Japanese language
• Natural selection.
• Paramecium -- Physiology.
• Protozoa -- Physiology.
• Vitalism.