Background

Herbert Spencer Jennings was born on April 8, 1868, in Tonica, Illinois, United States. He was the son of George Nelson Jennings, a physician, and the former Olive Taft Jenks.

Education

After attending local schools Jennings studied at Illinois State University. From 1890 to 1893 he attended the University of Michigan, where he met Jacob Reighard, a young zoologist, and ichthyologist. After obtaining the Bachelor of Science degree from Michigan and spending a year in a graduate study there, Jennings went on to work with Reighard’s teacher, E. L. Mark, at Harvard. There he took the Master of Arts degree in 1895 and the Ph.D. in 1896, submitting a thesis on the morphogenesis of a rotifer.

Career

In 1889-1890, through the influence of a former teacher Jennings was appointed an assistant professor of botany and horticulture at the Agricultural and Mechanical College of Texas. After finishing his doctorate Jennings held the Parker traveling fellowship, which took him to Jena in the winter of 1896-1897, where he worked with Max Verworn, a pioneer student of the behavior of protozoans. In the spring he went to the zoological station at Naples, to which he returned in 1903-1904 as one of the first scientists subsidized by the Carnegie Institution of Washington.

Upon returning to the United States, Jennings was without a position. In August 1897, he was called to the Agricultural College of Montana in Bozeman (now Montana Stale University) as professor of botany and horticulture. He spent the academic year 1898-1899 at Dartmouth as an instructor in zoology, and in 1899 he rejoined Reighard at Michigan as an instructor in zoology.

By 1901 he had advanced to assistant professor, but in 1903 he departed for an identical appointment at the University of Pennsylvania. Finally, in 1906, Jennings accepted an associate professorship of zoology at Johns Hopkins University. In 1907 the title was changed to professor of experimental zoology. He was named Henry Walters professor and director of the zoological laboratory in 1910. After his retirement in 1938, he became research associate at the University of California, Los Angeles. Although he did not have a great number of students, among them were T. M. Sonneborn, William Taliaferro, and Karl Lashley.

Jennings concentrated his attention upon only two types of microorganisms, the Rotifera and the Protozoa; but his research nevertheless mirrored the changes that were taking place in the shifting mainstream of biology. His first works were descriptive and systematic; he then turned his attention to physiology and adaptation; and finally took up the question of variation and reproduction and made major contributions to genetics.

The earliest phase of Jennings’ work is reflected in his publications for the Michigan State Board of Fish Commissioners and the U. S. Fish Commission, working under the direction, in each case, of Reighard, who saw to his employment during several summers. His descriptions and classifications of Rotifera, including new species, hold a respectable place in the systematic and morphological literature. At Harvard, C. B. Davenport helped kindle his enthusiasm for experimental methods; and Jennings’ work with the paramecium, undertaken with Verworn at Jena in 1897, began a decade of study of the behavior of the very simple organisms. This research resulted in a number of papers and, ultimately, in a book, Behavior of the Lower Organisms (1906).

Behavior of the Lower Organisms had an impact in three areas particularly. First, Jennings, unlike previous workers on the protozoa, studied the reactions of individual organisms rather than generalized or group behavior. He thus was able to raise questions about the specific processes and patterns involved when stimuli were followed by responses. Second, the book (and an earlier report of 1904) presented the first clear challenge, with experimental evidence, to the theory of physicochemical tropisms, of which Jacques Loeb was the chief exponent. Since most of the workers supporting the existence of tropistic behavior had utilized metazoic organisms, Jennings’ demonstration in even more primitive one-celled animals of phenomena that the concept of tropistic responses could not encompass was devastating to the theory, which eventually languished.

Finally, through his book, Jennings did much to bring very simple and one-celled organisms into the realm of psychology. Jennings now adapted to paramecia the use of experiment in comparative psychology, largely pioneered by E. L. Thorndike in 1898; and he asserted the identity of the basic nature of activity and reactivity in all animals, from protozoans to man. The idea was not new but Jennings’ experimental evidence was, and it appeared at the time to be conclusive.

With the completion of the book, Jennings turned away from the subject of animal adaptation and functioning. Even the course on animal behavior at Johns Hopkins was turned over to his new colleague and ally in the field, S. O. Mast. Jennings now embarked on four decades of research in the recently opened field of genetics, still utilizing the very smallest animals. Although again basing his work upon characteristics of individual organisms (aggregated statistically rather than studied in groups or swarms), he devoted himself “to what happens in the passage of generations in these creatures; to a study of the biology of races rather than of individuals, to life, death, mating, generation, heredity, variation and evolution in the Protista.”

In the course of his inquiry Jennings made numerous important contributions. As he systematically applied Mendelian theory, he helped to found mathematical genetics through his calculations of expectable ratios of traits in various types of inheritance. Of all of Jennings’ work in genetics, however, the most momentous was that in which he investigated the questions of variation and evolution.

Between 1908 and 1916 Jennings and his students published a number of papers on the constancy and variability of protozoan lines of inheritance. He was able to show that within a given species there exist a number of distinctive strains whose traits persist over many generations - essentially the kinds of variations that Darwin had discussed originally as providing the basis for the effects of natural selection. But Jennings also observed the spontaneous development of this type of variation, usually only a very slight - but a persisting - alteration. This work did much to modify the theory of mutations because the “saltations” that Jennings reported were very slight indeed and suggested that evolution must proceed gradually by very small changes.

After 1916 Jennings did much less laboratory work, instead producing a notable series of works popularizing genetics and discussing philosophical questions raised by the newer methods and discoveries in experimental biology. He discussed particularly the fundamental finding of his own lifework, that life processes are identical throughout all of the animal kingdom, for he had extended his contention from areas of reactivity to include inheritance. In the 1940s he even wrote about social phenomena among unicellular beings, a conception that grew out of the writings of W. C. Allee as well as his own renewed burst of laboratory research, an inquiry into the nature of sexuality in the paramecium.

As a youngster, Jennings had at first been interested in the humanities, and this interest appeared later in his published philosophical discussions. As early as the 1910s he had written in opposition to Driesch’s vitalism because, he asserted, he was afraid that biological experimentation that was purely scientific would be inhibited by vitalistic beliefs. He later wrote in a more positive vein about broader questions. For example, in the Terry lectures (published in 1933) on the relation between biology and religion, he affirmed the finality of death but also stressed the purposiveness of life and the compatibility of ethics with a strictly biological viewpoint.

Jennings assisted in editing a number of major journals and, through his influence within the powerful inner circles of American science, helped to develop the best traditions of experimental work in the United States.

Achievements

• Herbert Spencer Jennings was called as one of the first scientists “actually to see and control the process of evolution among living things.” The impact of Jennings upon science can be measured, at least in part, by his place in the literature. His popularizations of experimental biology were very widely read and cited; his book, Behavior of the Lower Organisms, is considered a classic of zoology and comparative psychology.
  
  Experimental methods that he introduced were still in use a generation or two later. Lines of investigation in genetics that he started or fostered were exciting and productive for at least half a century. For years he was the most conspicuous figure in new genetics developed in protozoology, complementary to but different from the classic Drosophila work. His thorough experimental procedures and clear thinking gained him respect among his colleagues that was reflected in prizes, honorary degrees, and lectureships.

Works

More photos

• book

  • Suggestions of Modern Science Concerning Education 1917
  • Contributions to the Study of the Behavior of Lower Organisms 1904
  • Genetic Variations in Relation to Evolution 1935
  • The Early Development Of Asplanchna Herrickii De Guerne 1896
  • Anatomy Of The Cat 1901
  • Life and death, heredity and evolution in unicellular organisms 1920

Views

Jennings was a eugenicist.

He contended, chiefly against Gary Calkins, that conjugation was not necessarily essential in maintaining the vitality of strains of one-celled animals, an opinion that he reversed at the end of his life.

Membership

Jennings was a Fellow of the Royal Society of Edinburgh, and member of the American Philosophical Society, the National Academy of Sciences and similar bodies.

Personality

At Johns Hopkins, Jennings was noted for his dedication to research and graduate instruction.

Connections

In 1898 Jennings married Mary Louise Burridge, who did many of the illustrations in his publications. His wife died in 1937; and in 1939 he married Lulu Plant Jennings, the widow of his brother.

Father:

George Nelson Jennings

Mother:

Olive Taft Jenks

Spouse:

Lulu Plant Jennings

late spouse:

Mary Louise Burridge

fellow student:

Jacob Reighard

mentor:

E. L. Mark

Student:

Tracy M. Sonneborn

Student:

William Taliaferro

Student:

Karl Spencer Lashley

colleague:

Charles Benedict Davenport

References

• Dictionary of Scientific Biography, Volume 7
  1973