Lehrman, Daniel Sanford
LEHRMAN, DANIEL SANFORD
(b. New York, New York, 1 June 1919; d. Santa Fe, New Mexico, 30 August 1972),
comparative psychology, ethology, behavioral endocrinology, instinct.
Lehrman was a comparative psychologist who made important contributions to the study of animal behavior both as a research scientist and as a critic of theory. He pioneered the field of behavioral endocrinology. His critique of ethological instinct theory led to an exchange of views between European and American scientists that did much to shape the subsequent evolution of the study of animal behavior.
Career . Lehrman grew up in New York City, where he attended public schools, including the elite Townsend Harris High School in the Bronx. He enrolled in the City College of New York, but his undergraduate studies were interrupted when he enlisted in the U.S. Army in 1942. During World War II his linguistic skills enabled him to serve as a translator of German and a cryptographer. Returning to City College he completed his BS degree, majoring in psychology and biology, in 1946. He then took up graduate study at New York University. There he worked under the direction of Theodore C. Schneirla, a noted comparative psychologist connected with the American Museum of Natural History. During this time he also worked as an assistant psychologist at the Haskins Laboratories (1945–1947), and held a summer fellowship at the Bronx Zoo. He completed his PhD in psychology in 1954. Meanwhile, he was appointed lecturer in psychology at City College (1947–1950), and then, in 1950, assistant professor in the Psychology Department of the Newark campus of Rutgers, the State University of New Jersey. He continued to give evening classes at City College until the early 1960s, partly because this served as a recruiting ground for the research program he was developing at Rutgers. In 1957–1958 he was a visiting professor at Yale.
In 1958 Rutgers promoted him to associate professor. In the same year he applied for and was awarded a sizable U.S. government grant to establish an animal behavior research facility in Newark. Thus he founded the Institute of Animal Behavior (IAB) at Rutgers, which grew to be internationally recognized for the quality of its science. This had Lehrman’s work at its center, but comparable contributions came from the several colleagues who joined him, and the numerous graduate students who did PhD research in the institute.
Despite proposals to move the institute closer to the main Rutgers campus in New Brunswick, and similar invitations from other universities, including Harvard, Lehrman remained loyal to his first employer and elected to stay in Newark. He was rewarded by enlarged quarters in a new building when the Newark campus was relocated as part of an urban renewal development in 1969. The new institute facility, which Lehrman took a considerable part in designing, was described by one visitor as “the Taj Mahal of animal behavior” (Richard Michael, personal communication to Colin Beer).
In 1963 Lehrman was appointed associate editor of the Journal of Comparative and Physiological Psychology, which enabled him to take a major part in promoting the publication of comparative work in animal behavior. He also collaborated (with Robert Hinde and Evelyn Shaw) in founding and editing a series of volumes, Advances in the Study of Behavior, for Academic Press. Beginning in 1955, he became a major figure in the biennial International Ethological Conferences, and was involved in numerous other meetings between representatives of European ethology and American comparative psychology. In 1970 he was invited to join the Salk Institute in La Jolla, California, as a resident fellow, but declined, accepting instead the status of a visiting fellow.
Lehrman’s contributions to science were recognized by the granting of a lifetime Research Career award from the U.S. Public Health Service, election to membership of the National Academy of Sciences, and a fellowship of the American Academy of Arts and Sciences. He was also honored by the Animal Behavior Society, the American Ornithologists’ Union, and other institutions.
Biological Background . Although “Danny” Lehrman’s academic training was mainly in psychology, his first love was natural history, especially that of birds. As a schoolboy he responded to the encouragement and example of his scoutmaster by joining bird walks with local ornithologists in such places as Van Cortlandt Park and the Brooklyn Botanic Garden. He developed a passionate interest in bird life, in addition to the birder’s affliction of needing to include as many species as possible on a life list of birds seen (he was still preparing to add to the tally on the day he died). Indeed this absorption with birds sometimes interfered with his college career, as he cut classes to indulge it so often, especially during migration times, that he was temporarily suspended.
During his first year at City College Lehrman began working part time at the American Museum of Natural History as a volunteer assistant to Kingsley Noble, curator in the Department of Experimental Biology (later the Department of Animal Behavior), whose work included bird studies. For instance, he was involved in a series of field experiments on what a laughing gull might treat as an egg, for which Lehrman did most of the tests. This earned him coauthorship of the resulting publication, although he was chagrined at having his interpretations of the observations ignored or overruled by the senior man. Indeed there are records suggesting that Noble consistently took advantage of the enthusiasm and enterprise of his young assistant. Nevertheless, Lehrman gained much from this involvement at the museum. He later recalled how the influences of other people there, including Frank Beach, William Etkin, Libbie Hyman, Ernst Mayr, and Ted Schneirla, turned his attention toward animal behavior and encouraged his pursuit of it. In their different ways Hyman and Schneirla introduced him to the conception of levels of organization in the animal kingdom, a viewpoint that influenced his thinking throughout the rest of his life.
It was also at the museum that Lehrman had his first close encounter with ethology, the European-based approach to the biology of behavior. In 1938 Niko Tin-bergen, one of the “fathers” of ethology, made his first trip to the United States, which included an extended visit to the museum. He and the young ornithologist met and got to know one another during bird walks in New York parks. In 1947 Tinbergen returned to New York at the invitation of the museum and Columbia University to give a series of lectures titled “The Study of Innate Behavior in Animals.” When the text of these lectures was accepted by Oxford University Press for publication as The Study of Instinct (1951), Danny Lehrman was given the task of polishing the Dutchman’s English into what remains one of the most readable texts in the animal behavior literature.
The other major figure in ethology’s founding also came to Lehrman’s notice during his “apprenticeship” at the museum. He began reading and translating Konrad Lorenz’s work, becoming so involved with it that Margaret Morse Nice, one of the luminaries of American ornithology at the time, invited him to review one of Lorenz’s major articles (“Vergleichende Verhaltensforschung,” 1939) for the journal Bird Banding. The review was published in 1941. Though critical of some points, such as Lorenz’s proneness to sweeping generalizations that ignored “the great differences in organization of the nervous system at different evolutionary levels,” Lehrman enthusiastically promoted the Lorenzian approach to the causes of behavior as “superior and more fruitful than any that can be obtained otherwise” (1941, p. 87). Lehrman even offered to lend his translation of Lorenz’s paper to anyone interested in the new orientation. There was little indication of the attack to be launched twelve years later.
Research: Interacting Causes of Bird Behavior . When Lehrman began work for his PhD under the direction of Schneirla in 1948, he naturally took up a project on birds. He settled on the breeding behavior of ring doves (Streptopelia risoria), partly because these birds were available at the museum and can be easily bred and observed in captivity. To begin with he took an amusingly wrong turn. He drew up a plan to study how incubation behavior might be meshed with changes in the brood patches. These are areas of ventral skin that become denuded of feathers and extensively vascularized in the service of conveying heat to the eggs when a bird is sitting on them. They are almost ubiquitous in birds that incubate their eggs this way, as does the ring dove. To his surprise Lehrman found his species to be an exception: there were no detectable changes in dermal state or sensitivity of the kinds he expected to be connected with a dove’s tendency to sit on eggs.
Consequently he turned to another feature that also sets pigeons and doves apart from other birds: the way they feed their young. At around the time the eggs hatch, the epithelial lining of the crop of the sitting birds begins to change texture, exuding a substance having the consistency and nourishing properties of mammalian milk. It is referred to as crop milk, and the hungry nestlings (squabs) ingest it by inserting their bills into the parent’s mouth and having the parent regurgitate. Lehrman set about investigating how the production of crop milk is induced, and the joint contributions of parent and young to the feeding process. This led to his getting involved with behavioral endocrinology, since crop milk production, like mammalian lactation, is due to secretion of the hormone prolactin from the anterior pituitary gland. Lehrman looked at how the hormone might otherwise be involved in the regurgitation feeding behavior. He found that when he injected prolactin into adult doves with previous breeding experience they responded to hungry squabs by feeding them, in contrast to control birds injected with the hormone vehicle, which ignored the squabs.
However, hormone-treated birds lacking previous breeding experience also failed to respond to the squabs. And so did experienced birds whose crops had been anesthetized. These results supported the conjecture that prolactin promotes feeding behavior in the doves by causing engorgement of the crop tissue, a condition from which the bird is relieved by regurgitation. This is initially invoked by tactile stimulation from a newly hatched squab’s thrusting its head upward against the parent’s breast. As a consequence the parent dove comes to associate the other features of a squab—its appearance and vocalization—with the relief from crop engorgement afforded by feeding it (Lehrman, 1955). This kind of story, in which hormones, stimulation, experience, and behavior are linked in dynamic and reciprocal relation, became a Lehrman leitmotif as he went on to experiment with other aspects of the ring dove breeding cycle, and apply its lessons to comparable systems in other kinds of animals.
For example, further study of the role of prolactin in incubation showed that its secretion is a consequence of the initiation of sitting on eggs. This is induced by another hormone, progesterone, produced by the gonads, together with the visual stimuli from the nest and eggs. The consequent tactile stimulation leads to changes in the brain affecting the release of prolactin. This part of the process involves a vascular link, discovered by Geoffrey Harris (1955), which conveys a humoral agent from the hypothalamus to the anterior pituitary. The prolactin has the effect of sustaining incubation, as well as preparing for the next phase of the cycle by inducing crop milk production. Tracing the chain of causal command still further back, Lehrman was able to show how the gonadal development responsible for progesterone secretion depends upon the previous events of courtship, copulation, and nest building. These involve visual, auditory, and tactile stimulation, which act via the hypothalamic-pituitary link to mobilize gonad-stimulating hormone; this, in addition to gametogenesis, induces secretion of sex steroids, which feed back to the brain to produce changes in behavior and modulate pituitary output. Thus internal and external factors—stimuli, brain states, endocrine secretion, behavior—take turns as cause and effect in the complex progressive succession that is the ring dove breeding cycle (e.g., Lehrman, 1965).
Lehrman’s work on the doves bore comparison to that of his friend Robert Hinde at Cambridge University. Hinde’s studies of the breeding behavior of canaries revealed a similar pattern of reciprocal relations along with differences of detail. Likewise Lehrman’s close colleague at the IAB, Jay Rosenblatt, demonstrated in numerous ways the intertwined and detailed connections between behavioral development of the young and associated maternal behavior in rats, cats, and other mammals.
When William C. Young invited Lehrman to contribute a chapter on “Hormonal Regulation of Parental Behavior in Birds and Infrahuman Mammals” for a new edition of Sex and Internal Secretions (1961), he was very well placed to do so and readily undertook the task. In this now-classic survey Lehrman reviewed in depth and detail the extensive relevant literature in behavioral endocrinology, bringing to bear his unique combination of synthetic and analytic judgment, making connections and drawing distinctions; for the chapter continues to be consulted, in contrast to the ephemeral life of most such scientific writing, and in spite of the newer work it has in part inspired.
At the International Ethological Conference held at Cambridge University in 1959 Lehrman gave a talk indicating that he was off on a new tack. He described a method by which behavioral data recorded by an observer using a keyboard might be coded and fed into a computer for immediate data reduction and statistical analysis. Despite considerable expense of time and effort this ambitious project proved too cumbersome to be practical and never got off the ground.
This gravitation to computer technology was consistent with one of Lehrman’s predilections, but the grandiose scale of his scheme was at odds with the kind of stance he generally took toward programs of comparable scope. He was critical of learning theorists, such as Clark Hull and Edward Chace Tolman, for their assumption that learning conforms to universal laws, and hence their failure to take into account the profound differences consequent on the levels of organization that separate different kinds of animals. He also found fault with European ethology for failure to draw necessary distinctions. But this was only part of an extended critique that shook up “classical” ethology to such an extent that it underwent profound regrouping. It also made Daniel Lehrman a voice to be reckoned with in the larger world of behavioral science.
Critique of Ethology: Instinct . Lehrman was still working on his PhD when he published “A Critique of Konrad Lorenz’s Theory of Instinctive Behavior” (1953). Many people regarded it as an audacious move on the part of a young man who had yet to make his mark as a figure in the field of behavioral studies. It would have been thought even more so had he not been dissuaded from including passages of invective directed at Lorenz’s pro-Nazi, anti-Semitic wartime writings, which Lehrman had translated.
Lehrman saw ethological instinct theory, Tinbergen’s along with Lorenz’s, as a product of the mischief of ambiguity of the term instinct. The word can have several distinct meanings, which do not logically entail one another: genetically transmitted behavior, behavior that does not depend upon experience for its development (i.e., is not acquired by learning), and motivational impulsion or blindingly compelling urge (e.g., maternal instinct), action based on impulse rather than deliberation. Lorenz (1950) had claimed that ethology owed its existence to discovery of a type of behavior, the Instinkthandlung or fixed action pattern, to which all the salient senses of “instinct” apply: it is innate both in the sense of being genetically inherited and in the sense of being independent of learning; its performance is both endogenously impelled by centrally generated energy for which it serves as outlet and goal, and endogenously patterned or controlled (in contrast to peripheral reflexes). Tinbergen’s (1951) version expanded “instinct” to the status of a whole hierarchically organized motivational system serving one of the major functional divisions, such as foraging and reproduction, which incorporated fixed action patterns as terminal components. It too was supposed to be inborn, developmentally preprogrammed, and endogenously driven.
Lehrman took issue with the central assumption of these systems, according to which innate in the sense of heredity implies innate in the sense of not learned: evidence of genetic transmission is not, ipso facto, evidence bearing on the role of experience in development. The fact that Rudolf Serkin was a superb concert pianist did not absolve his comparably gifted son Peter from having to practice. Lehrman argued that the ethological position on questions of behavioral development was usually based either on invalid extrapolation from genetic considerations, or flimsy observations or experiments, such as the Kasper Hauser procedure of raising animals in social isolation (named for a youth treated this way who was found wandering the streets of Nürnberg in 1882), which attempts to exclude from experience whatever might be thought to be relevant. Lehrman contended that insufficient consideration was given to what deprivation might have failed to exclude, pointing to cases of possible prenatal learning or an animal’s using part of its own body in lieu of what it had been kept from. Admittedly some of his examples were far fetched, but the general point that questions of development require their own study, and cannot be answered by breeding experiments, was compellingly made. Similarly he maintained that the fixity of fixed action patterns was usually more a matter of assertion than experimentally established fact.
Furthermore, Lehrman challenged the physiological plausibility of the motivational mechanisms proposed by Lorenz and Tinbergen. On the one hand the main evidence for them appeared to be the alleged features of observed behavior they were supposed to explain. Apart from some appeal to work by Charles Sherrington, Erich von Holst, and a few others with physiological credentials, the mechanisms were unsupported by independent physiological investigation, and hence could be regarded as “reifications.” On the other hand the relevant physiology was at odds with the hydraulic analogies informing the motivational models: neural excitation is not the kind of thing that can accumulate, overflow, or be “dammed up.”
Finally, as with monolithic learning theory, Lehrman deplored the undiscriminating inclusiveness of instinct theory: “reification of the concept of ‘instinct’ leads to a ‘comparative’ psychology which consists of comparing levels in terms of resemblances between them, without that careful consideration of differences in organization which is essential to an understanding of evolutionary change, and of the historical emergence of new capacities” (1953, p. 351). He was particularly bothered by the “patently shallow” (p. 353) attempts to comprehend the human case within instinct’s purview.
Although Lehrman’s critique landed like a bombshell in the precincts of ethology, the ground had been prepared for it to some extent. In 1950 there had been a meeting on ethological terminology, which had recommended against continued talk of “action specific energy” with its controversial material connotations. Especially in Britain, a younger generation of ethologists, led by Robert Hinde, had begun questioning the utility of the hydraulic models, taking a tough-minded, often statistical stance toward the grounding of concepts, in contrast to the tender-minded speculations of the founding fathers. Lehrman’s arrival on the scene thus encountered a mixture of hostility and welcome.
It did not take long for confrontation to reach the conference table. In 1954 two important meetings on the issues dividing European ethology and American comparative psychology took place, the first in Paris under the auspices of the Singer-Polignac Foundation, the second in Ithaca, New York, sponsored by the Macy Foundation. Lehrman was a key figure in both of these. The following year an American contingent, again including Lehrman, was invited to the Third International Ethological Conference in Groningen, Netherlands.
These and other such opportunities to try to come to terms did much to reduce transatlantic tension and misunderstanding. “Hard core” classical ethologists, such as Gerard Baerends and Jan van Iersel, were surprised to have their “rat runner” stereotype of the American animal psychologist confounded by a Lehrman who knew as much about wild birds as they did. By 1967, when the Ethology Conference convened in Stockholm, much of the dissension had dissipated, thanks in part to Lehrman’s consistent attendance at these meetings. Apropos the Stockholm conference, Lorenz wrote in a letter to Tinbergen: “I believe Danny Lehrman has now finally understood me, and we have both in many discussions astonishingly come to exactly the same thing” (quoted in Burkhardt, 2005, p. 405).
Nevertheless, some of the old divisions had merely been pasted over, and it did not take much to make the cracks show. In 1965 Lorenz published Evolution and Modification of Behavior, which returned to the nature/nurture issue, albeit with a new twist, which relocated the dichotomy to genetic and environmental sources of “information” contributing to behavioral development. He argued that whenever behavior shows adaptive design it must be a product of naturally selected specification encoded in the genome; hence if learning is developmentally involved it must be due to an “innate schoolmarm” (p. 80). He also accused “N. Tinbergen and many other ethologists writing in English” (p. 1) of apostasy, and lumped Lehrman indiscriminately with the behaviorists.
Lehrman responded to this book in the chapter he wrote for a memorial to his mentor T. C. Schneirla. He objected to the way he and Schneirla had been represented as ignorant of biology, and to Lorenz’s tactic of defending his position on the innate/learned dichotomy by shifting the goal posts. However, his main point was that the issues were less about matters of fact than due to deep-seated ideological differences, which were abetted by conceptual and semantic confusions. He maintained that Lorenz’s obsession with questions of adaptive function had blinded him to the true nature of questions about proximate causation and individual development:
It is not necessary that all problems fit into the same conceptual framework. It is not required of any theory based on watching intact lower vertebrates that it explain the causes of war, the physiology of the nervous system, and also the mode of action of the genes; and it is not an affront to any theory to point out that there are some questions that it cannot answer because it has not asked them. (Lehrman, 1970b, pp. 47–48)
Beyond Behavior . A charismatic teacher in the classroom and forceful speaker on the podium, Lehrman sometimes took advantage of the stage to express opinions on topics of broader concern than the issues of behavioral science. Two examples will have to suffice.
Lehrman’s political sympathies tended to favor left-wing causes. Among these was feminism, to which his wife Dorothy Dinnerstein was to make a now classic contribution with her book The Mermaid and the Minotaur (1976). In September 1970, Lehrman gave a talk at a symposium in Canada on “The Application of Ethology to Human Growth and Development.” The audience included a substantial number of psychiatrists. Using birds as his main examples, but also drawing on monkey comparisons presented by previous speakers, he made the point that even closely related species can differ profoundly in their ecological and social relationships in ways affecting behavioral development. Hence it can be erroneous to generalize from one species to another without taking into account how natural selection might have differentially designed their domestic arrangements, especially when appealing to animal comparisons to support views about what is natural for the human case: from the fact that a rhesus monkey infant suffers lasting psychological impairment from a period of separation from its mother, it does not necessarily follow that woman’s place is in the home (Lehrman, 1974).
As part of the centenary celebrations of the American Museum of Natural History, Lehrman found himself sharing the limelight with Burrhus Frederic Skinner. He contrasted his own “natural history” approach to animal behavior with Skinner’s behavioral engineering, which he took to be essentially concerned with using animals to study how contingencies of reinforcement can serve as means of controlling, shaping, and predicting behavior in general, including the behavior of people. For Lehrman the study of animal behavior was something to be undertaken for its own sake, more akin to the appreciation of poetry than the pursuit of power. Of science in general he said:
In addition to (or instead of) serving a function like that of an engineer, the scientist can also serve a function like that of an artist, of a painter or poet—that is, he sees things in a way that no one has seen them before and finds a way to describe what he has seen so that other people can see it in the same way. This function is that of widening and enriching the content of human consciousness, and of increasing the depth of the contact that human beings, scientists and nonscientists as well, can have with the world around them. (Lehrman, 1971, p. 471)
On 27 August 1972, in Santa Fe, New Mexico, Danny Lehrman suffered a heart attack and died three days later. He was only fifty-three. The following year the International Ethological Conference was held in Washington, D.C. The program included a full-day plenary session in tribute to Lehrman’s work and character, the only such memorial in the history of these meetings. The man who entered the ethological scene as an antagonist left it as a hero.
WORKS BY LEHRMAN
With C. K. Noble. “Egg Recognition by the Laughing Gull.” Auk 57 (1940): 22–43.
“Comparative Behavior Studies.” Bird Banding 12 (1941): 86–87. This was a review of K. Z. Lorenz, “Vergleichende Verhaltensforschung.” Verhandlungen der deutschen zoologischen Gesellschaft, edited by C. Apstein. Zoologische Anzeiger, supp. 12. Leipzig, Germany: Akademische Verlagsgesellschaft m.b.H., 1939.
“A Critique of Konrad Lorenz’s Theory of Instinctive Behavior.” Quarterly Review of Biology 28 (1953): 337–363.
“The Physiological Basis of Parental Feeding in the Ring Dove (Streptopelia risoria).” Behaviour 4 (1955): 241–286.
“Induction of Broodiness by Participation in Courtship and Nest-Building in the Ring Dove (Streptopelia risoria).” Journal of Comparative and Physiological Psychology 51 (1958): 32–36.
“Hormonal Responses to External Stimuli in Birds.” Ibis 101 (1959): 478–496.
With P. N. Brody and R. P. Wortis. “The Presence of Mate and of Nesting Material as Stimuli for the Development of Incubation Behavior and for Gonadotropin Secretion in the Ring Dove (Streptopelia risoria).” Endocrinology 68 (1961): 507–516. “Hormonal Regulation of Parental Behavior in Birds and Infrahuman Mammals.” In Sex and Internal Secretions, 3rd ed., edited by W. C. Young. Baltimore: Williams and Wilkins, 1961.
“Interaction of Hormonal and Experiential Influences on Development of Behavior.” In Roots of Behavior, edited by E. S. Bliss. New York: Harper and Row, 1962.
With J. S. Rosenblatt. “Maternal Behavior of the Laboratory Rat.” In Maternal Behavior of Mammals, edited by H. L. Rheingold. New York: Wiley, 1963.
“On the Initiation of Incubation Behavior in Doves.” Animal Behaviour 11 (1963): 433–438.
“Control of Behavior Cycles in Reproduction.” In Social Behavior and Organization among Vertebrates, edited by W. E. Etkin. Chicago: University of Chicago Press, 1964.
“Interaction between Internal and External Environments in the Regulation of the Reproductive Cycle of the Ring Dove.” In Sex and Behavior, edited by F. A. Beach. New York: Wiley, 1965.
“Experiential Background for the Induction of Reproductive Behavior Patterns by Hormones.” In Biopsychology of Development, edited by E. Tobach, L. R. Aronson, and E. Shaw. New York: Academic Press, 1970a.
“Semantic and Conceptual Issues in the Nature-Nurturem Problem.” In Development and Evolution of Behavior, edited by L. R. Aronson, E. Tobach, D. S. Lehrman, and J. S. Rosenblatt. San Francisco: Freeman, 1970b. Lehrman’s response to Lorenz’s Evolution and Modification of Behavior.
“Behavioral Science, Engineering, and Poetry.” In The Biopsychology of Development, edited by E. Tobach, L. R. Aronson, and E. Shaw. New York: Academic Press, 1971.
“Can Psychiatrists Use Ethology?” In Ethology and Psychiatry, edited by Norman F. White. Toronto: McMaster University Press, 1974.
Beer, C. G. “Was Professor Lehrman an Ethologist?” Animal Behaviour 23 (1975): 957–964. Text of a talk given in the Lehrman Memorial Plenary Session at the 13th International Ethological Conference in Washington, DC, August 1973.
Burkhardt, Richard W. Patterns of Behavior: Konrad Lorenz, Niko Tinbergen, and the Founding of Ethology. Chicago: University of Chicago Press, 2005.
Dinnerstein, D. The Mermaid and the Minotaur: Sexual Arrangements and Human Malaise. New York: Harper and Row, 1976.
Harris, G. W. Neural Control of the Pituitary Gland. London: Edward Arnold, 1955.
Lorenz, Konrad Z. “The Comparative Method in Studying Innate Behaviour Patterns.” Symposia of the Society for Experimental Biology 4 (1950): 221–268. Lorenz’s best-known version of his instinct theory in English.
———. Evolution and Modification of Behavior. Chicago: University of Chicago Press, 1965.
Rosenblatt, J. S. “Daniel Sanford Lehrman 1919–1972.” Biographical Memoirs, vol. 66. Washington, DC: National Academy of Sciences, 1995.
Tinbergen, N. The Study of Instinct. Oxford: Clarendon Press, 1951. The classic thesis of classical ethology.
———. “On Aims and Methods of Ethology.” Zeitschrift für Tierpsychologie 20 (1963): 410–433. Famous for its statement of “the four questions of ethology” with which Lehrman was in harmony.