JENNINGS, HERBERT SPENCER

(b. Tonica, Illinois, 8 April 1868; d. Santa Monica, California, 14 April 1947),

animal behavior, physiology, genetics, protozoology, zoology, philosophy of science. For the original article on Jennings see DSB, vol. 7.

Since the original DSB article was published, new light has been shed on Jennings’s approach to science, especially his epistemology and experimental method; his views on inheritance; and his political views, especially concerning eugenics.

Herbert Spencer Jennings was a leader in the experimentalization of zoological research in the United States in the first decades of the twentieth century. Beginning with his postdoctoral research on the behavior of lower organisms carried out between 1896 and 1906, and continuing with his studies of heredity and variation from 1907 through the remainder of his career, Jennings championed the use of experiment for biological study. Jennings’s methodological orientation was deeply informed by his adherence to pragmatism, as articulated primarily by the philosophers John Dewey and William James. By 1913 Jennings formulated his own philosophy of biology, termed “radically experimental analysis,” which bore many of the hallmarks of pragmatism, including a relentless commitment to action and to empiricism for the resolution of scientific problems. As a pragmatist, Jennings directed these same priorities to the social arena as well.

Jennings’s pragmatism informed all aspects of his career, from his behavioral and genetics research programs with protozoa, to his substantial philosophical writings, to his public criticisms of eugenics during the 1920s.

Jennings’s contact with pragmatism began early in his education, when he pursued two years of philosophical study with the young Dewey between 1890 and 1892, while an undergraduate at the University of Michigan. Jennings had already had considerable contact with literature and philosophy as a young child who passed much of his time reading widely from the large library of his father, George Nelson Jennings. The senior Jennings was a physician and enthusiastic evolutionist, who named his first-born son for the influential British philosopher, Herbert Spencer, while naming his second son George Darwin. The young Herbert Spencer Jennings came to reject much of the Spencerian thought that he had adopted at an early age when he was exposed to Dewey’s experimentalism. Dewey claimed that ethical behavior was grounded not in natural law, as had been held by Spencer, but in scientific method. While ultimately pursuing a course of study in zoology, culminating in earning his PhD in zoology at Harvard University in 1896, Jennings never lost interest in philosophy and its relevance for political and scientific conduct.

In his dissertation research, Jennings had been deeply interested in the experimental goals and methods but largely critical of the mechanistic orientation of the new experimental program of development mechanics, or Entwicklungsmechanik, championed by Wilhelm Roux and others. Developmental mechanics imported experimental methods from the field of physiology to zoology, which until that time was largely characterized by the observational practices of natural history. Inspired by the new experimentalism, Jennings pursued postdoctoral study in the laboratory of the German physiologist Max Verworn in Jena in 1896–97. There, Verworn introduced Jennings to many of the experimental methods of physiology as well as to the microscopic single-celled organisms, the protozoa, for experimental study. Jennings was also further immersed in the evolutionism that suffused Jena, the epicenter of German evolutionary thought. Throughout his career, Jennings, like Verworn and his Jena colleague, Ernst Haeckel, embraced the protozoa for their biological importance as organisms possessing complex physiological processes and behaviors, yet were at the same time single cells.

Relatively early in his physiological studies of the behavior of protozoa, Jennings emphasized the rudimentary psychological capabilities of the organisms. In the course of this research he characterized the essential features of the avoiding reaction in protozoa, the process by which the microscopic organism stops its forward motion, swims backwards, and then starts off in a new direction when it confronts a new external stimulus. Jennings rejected the idea that external, physicochemical forces causally directed the organism’s motions, as others such as Jacques Loeb claimed. He maintained that the avoiding reaction was driven by a mechanism internal to the organism. During a year of research at the Zoological Station in Naples, Italy, in 1903–04, however, he adopted a more radical position: Jennings now argued that the avoiding reaction in protozoa was an early manifestation of the method of “trial and error” deemed by the evolutionary psychologist C. Lloyd Morgan to be fundamental to the development of intelligence in higher organisms. This research culminated in the publication of his influential text Behavior of the Lower Organisms in 1906. During the same year Jennings accepted an appointment at the Zoological Laboratory at The Johns Hopkins University, which he directed from 1910 until he retired in 1938. (For discussion of the various academic positions held by Jennings prior to moving to Johns Hopkins, please see the original DSB article.)

Behavior of the Lower Organisms attracted considerable criticism both for its critical stance toward mechanistic biology and for its attribution of a developmental-evolutionary continuum “from the lowest organisms up to man” (p. 335) in behavioral features such as perception, choice, attention, and even consciousness. In the years that followed, Jennings dedicated considerable effort to epistemological writings informed by these earlier criticisms. Throughout his philosophical reflections he championed both a natural history-like attention to the individual organism and experiment in biology. Central to his concern was the development of a middle position in biology between vitalism on the one hand and mechanism on the other. Jennings was particularly concerned about the vitalism articulated by the German zoologist Hans Driesch, who maintained that two biological systems that are completely identical could behave differently under identical conditions. Jennings rejected Driesch’s position of experimental indeterminism, because it threatened to halt experimental inquiry in biology altogether. Arising from these concerns was Jennings’ formulation of his methodology of radically experimental analysis, whereby all biological questions are reduced to an experimental situation; in a given experimental situation, a preceding perceptual difference is sought for every existing perceptual difference.

In 1907 Jennings turned his attention from behavior to problems of heredity and variation. Following the rediscovery of Mendel’s laws in 1900, biological interest in heredity quickly blossomed as experimentation grew in prominence among academic biologists. Jennings was in the vanguard of American zoologists to publish experimental research in heredity and genetics in the first decade of the twentieth century. As researchers experimented with a variety of organisms, Jennings initiated experimental studies with the same organisms that had been central to his behavior research: the protozoa, and primarily the ciliate Paramecium. Conceptually, Jennings likewise presented his research program in heredity as a continuation of his behavioral research, focusing on the inheritance of adaptive qualities, a problem that he viewed as intimately related to the development of adaptive behaviors in an individual organism. There was methodological continuity between the two research programs as well; Jennings aimed to maintain analytical focus on the individual organism and on relationships between individual organisms in his hereditary studies. This was quite a distinctive undertaking, as the developing protocols in genetics research also demanded statistical analysis of data derived from large quantities of organisms, a methodological domain in which Jennings was also a leader.

Whereas Jennings engaged in important statistical and theoretical work in the 1910s and 1920s that lent credence to Mendelism and chromosome theory, his own experimental research program was not Mendelian. Like those of other leading zoologists attracted to the study of heredity during the period, the broader intent of Jennings’s research program was to demonstrate evolution experimentally. Furthermore, he aimed to uncover the most fundamental mechanisms of heredity and to advance a generalized conception of heredity. Unlike many, however, Jennings adopted a relatively pluralistic attitude toward the study of heredity. During this period he evenhandedly explored both selection and the inheritance of acquired characteristics as possible mechanisms of heredity and evolution. Jennings placed a great emphasis on the utility of the protozoa for such research, because their single cellularity made their exposure to environmental influences more feasible and hereditary effects in them more readily observable. Likewise, their uniparental form of reproduction made it possible to explore minute sources of heritable variation unobscured by biparental inheritance. Jennings came to view lineages of asexually reproducing protozoa as material embodiments of pure lines. Between 1909 and 1911 he facilitated discussions that helped to solidify the pure line and genotype concepts introduced by Wilhelm Johannsen.

The experience of World War I and the international political upheaval in the years that immediately followed was a transformative experience for Jennings, as it was for many scientists of his generation. Distress over growing American nativism in the postwar years and the associated rise of the eugenics movement prompted Jennings to largely abandon his experimental research program and dedicate his efforts throughout the 1920s to public criticism of eugenics. Jennings employed diverse strategies in this undertaking: He criticized fallacious reasoning and faulty assumptions underlying many eugenic arguments; in concert with social workers and educators, he countered genetic determinism by underscoring the role of environment and education in the development of human potential; and he worked to keep the field of genetics institutionally separate from the broader eugenics movement. At the end of the decade Jennings returned to experimental research with a narrowed research agenda. In a bid to generate new evidence further undercutting the eugenics movement, he reestablished a research program with Paramecium aimed at conclusively demonstrating the inheritance of environmental effects. The research planned by Jennings was largely carried out by his former student and research associate Tracy Sonneborn, and long-time research assistant Ruth Stocking Lynch. This work led to Sonneborn’s discovery of mating types in Paramecium aurelia in 1937.

Jennings served in many leadership capacities and received many honors in the course of his career. He served as president of the American Society of Zoologists (1909) and the American Society of Naturalists (1910), First Chairman of the Genetics Society of America (1922), Vice-President of Section F (Zoology) of the American Association for the Advancement of Science (1925), and member of the Council of the National Academy of Sciences (1934–1940). He served as a founding member of the editorial boards of The Journal of Experimental Zoology and Genetics and on the editorial boards of several other journals. He was a Terry Lecturer at Yale University (1933), Vanuxem Lecturer at Princeton University (1934), Eastman Visiting Professor at Oxford University (1935–1936), Leidy Lecturer at the University of Pennsylvania (1940), and Patten Lecturer at Indiana University (1943).

SUPPLEMENTARY BIBLIOGRAPHY

WORKS BY JENNINGS

Herbert Spencer Jennings Papers. Philadelphia, PA: American Philosophical Society Library. Contains extensive correspondence, notebooks, journals, manuscripts and lectures.

“Diverse Ideals and Divergent Conclusions in the Study of Behavior in Lower Organisms.” The American Journal of Psychology 21 (1910): 349–370.

“Doctrines Held as Vitalism.” The American Naturalist 47 (1913): 385–417.

“Causes and Determiners in Radically Experimental Analysis.” American Naturalist 47 (1913): 349–60.

“Heredity and Environment.” Scientific Monthly 19 (1924): 225–38.

“Diverse Doctrines of Evolution, Their Relation to the Practice of Science and of Life.” Science 65 (1927): 19–25.

OTHER SOURCES

Kingsland, Sharon. “A Man Out of Place: Herbert Spencer Jennings at Johns Hopkins, 1906–1938.” American Zoologist 27 (1987): 807–817.

Pauly, Philip J. “The Loeb-Jennings Debate and the Science of Animal Behavior.” Journal of the History of the Behavioral Sciences 17 (1981): 504–515.

Schloegel, Judith Johns. “Intimate Biology: Herbert Spencer Jennings, Tracy Sonneborn, and the Career of American Protozoan Genetics.” PhD dissertation. Bloomington: Indiana University, 2006.

———, and Henning Schmidgen. “General Physiology, Experimental Psychology and Evolutionism: Unicellular Organisms as Objects of Psychophysiological Research, 1877–1918.” Isis 93 (2002): 614–645.

Sonneborn, Tracy M. “Herbert Spencer Jennings, April 8, 1868–April 14, 1947.” Biographical Memoirs of the National Academy of Sciences 47 (1975): 143–223. A detailed biographical resource including a complete bibliography of Jennings’s publications and listings of positions, honors, and distinctions.

Judith Johns Schloegel