The Robert M. Yerkes Papers provide a rich resource for anyone interested in the history of
twentieth century psychology. They comprehensively document the life and career of Robert
Mearns Yerkes, one of the foremost psychologists of the first half of the century. In addition, his
extensive correspondence and broad research and professional interests make the papers an
indispensable collection for those interested in the development of psychology in the United States.
The major portion of the Yerkes Papers were deposited at the Yale Medical Library in 1962, were
subsequently transferred to Manuscripts and Archives, and finally donated to Yale University by
deed of gift in 1980.
The Yerkes Family, especially Roberta Yerkes Blanshard, daughter of Robert Yerkes, devoted a
great deal of attention to processing and arranging the Yerkes Papers, which were originally divided
into two major segments. The first part consisted of alphabetically arranged correspondence files
for individuals and subject correspondence files. The second segment was designated the Yerkes
Supplementary File and consisted primarily of teaching papers, student papers, experiments,
publications, photographs, family materials, and diaries. These two segments have been combined
and merged to produce the present arrangement for the Robert M. Yerkes Papers. The
organizational structure established by Helen Morford, Yerkes' secretary, has essentially been
preserved and future researchers owe a great debt of gratitude to her and the family for maintaining
such a complete record of the life of Yerkes and for the hundreds of hours of labor required to
logically and rationally organize the papers.
The Yerkes Papers provide documentation for researchers interested in a wide variety of subjects
and contain correspondence to, from, and about hundreds of people. It is, therefore, only possible to
discuss some of the more significant topics addressed in the papers and list the names of just a
sample of individuals concerned with these subjects.
The Robert M. Yerkes Papers are divided into six series. Series I, PROFESSIONAL
CORRESPONDENCE, contains extensive correspondence relating to anthropoid research and such
other subjects as intelligence testing, eugenics and immigration restriction, Yerkes' other research
activities, and the growth and development of the discipline of psychology. Series II, SUBJECT
FILES, covers the same subjects and has also material on the teaching and publishing activities of
Yerkes. Series III consists primarily of notes on experiments with chimpanzees and gorillas, while
Series IV, WRITINGS, contains copies of his published books and articles. Series V is composed of
photographs, both professional and personal, and Series VI, PERSONAL PAPERS, includes a wide
variety of autobiographical and biographical material about Yerkes, family correspondence, and a
series of diaries kept by Robert M. Yerkes.
Series I is called PROFESSIONAL CORRESPONDENCE. The material is arranged alphabetically
by surname of correspondent and is contained in Boxes 1-54 of the Yerkes Papers.
Robert M. Yerkes is best known for his studies of anthropoid apes, in particular for his extensive
work on chimpanzee and gorilla behavior. As early as 1913, Yerkes understood the importance of
scientific study of anthropoid apes and the need for an anthropoid research station to properly
pursue this work. In letters written between 1913 and 1916, he discussed his hopes with such people
as Abraham Flexner, Simon Flexner, Gilbert Van Tassel Hamilton, Alfred G. Mayer, Adolph
Meyer, Raymond Pearl, Edward W. Scripps, and William H. Welch. Additional information on his
plans for the study of anthropoid apes can be found in Series II, Box 57, folders 1088-1091. Not
until 1923 and 1924, however, was he given the opportunity to study apes. Through the good
offices of William T. Hornaday, director of the New York Zoological Society, folder 2121, Yerkes
purchased Chim and Penzee, and the following year travelled to the Cuban estate of Rosalia Abreu
to study her primates. See folders 3, 6-10, and 497 and Box 172, folder 2666. These Labors
culminated in the publication of his first book on apes, Almost Human, in 1925. That same year
Yerkes had the chance to study a young female gorilla called Congo, the results of which appeared
in The Mind of a Gorilla, published in three parts between 1926 and 1928. Correspondence
concerning Congo can be found in the folders for Benjamin Burbridge, John Ringling, and Richard
D. Sparks. See also Series III, EXPERIMENTS, Boxes 114-115.
Yerkes came to Yale in 1924, due largely to the efforts of Yale President James R. Angell, who was
able to provide research facilities in the recently established Institute of Psychology. The
university's support proved essential for the realization of Yerkes' dream to establish a primate
research center. With additional support from foundations, his Anthropoid Experiment Station was
established in Orange Park, Florida in 1929. It soon became known as the Yale Laboratories of
Primate Biology and after his retirement as the Yerkes Laboratories of Primate Biology. For
information about the establishment of and developments at the research station see the files for
James R. Angell, Roswell P. Angier, Harold C. Bingham, Raymond Dodge, John C. Merriam and
Herbert W. Rand. Additional material on research carried on at the laboratories can be found in the
folders For such research assistants as James H. Elder, Louis W. Gellerman, Carlyle F. Jacobsen,
Thomas L. McCulloch, Austin H. Riesen, Kenneth W. Spence and Otto L. Tinklepaugh. A great
deal of further material on the Yerkes Laboratories can be found in Series II, Boxes 107-112. Until
Yerkes' retirement in 1941, Yale served as the sponsoring institution for the Orange Park facility,
but with the appointment of Karl S. Lashley as director, sponsorship of the laboratories was jointly
shared by Harvard and Yale. See Box 109, folders 2038-2039. By the early 1950's, however, both
institutions sought to be relieved of their responsibilities for the Yerkes Laboratories. Professor
Yerkes was, of course, concerned about the future of the laboratories, a subject discussed in the
period 1951-1955 in the correspondence of such individuals as Leonard Carmichael, Donald Hebb,
Robert S. Morison, Arthur F. Perry, Jr., and Arthur J. Riopelle. See also Box 110, folders
2057-2060 for correspondence with Karl S. Lashley and Henry W. Nissen on the same subject. In
1956 title to the Yerkes Laboratories was transferred to Emory University. Eight years later they
were moved to Atlanta and rededicated on October 27, 1965 as the Yerkes Regional Primate
Research Center. See the files for Arthur J. Riopelle in Series I and Box 111, folders 2061-2063 and
Box 112, folder 2110 for information on the history of the Yerkes Laboratories after the death of
Robert M. Yerkes.
Yerkes was also known for his psychological testing of military personnel in World War I, in reality
intelligence testing. These matters, in particular Yerkes' testing work in World War I, are treated at
length in Series II, SUBJECT FILES. Some information on psychological testing in World War I,
however, can be found in the correspondence of Yerkes with Walter B. Cannon and Henry A.
Shaw. Yerkes had been interested in intelligence testing prior to World War I, having published A
Point Scale for Measuring Mental Ability with James W. Bridges and Rose S. Hardwick in 1915.
Material on intelligence testing can be found in the correspondence of such individuals as John F.
Anderson, J. W. Baird, Edwin G. Boring, James W. Bridges, Carl C. Brigham, Mabel R. Fernald,
Rose S. Hardwick, William Healy, A. A. Roback, Celio S. Rossi, Carl E. Seashore, Lewis M.
Terman, William H. Welch and Helen T. Woolley. The results of these tests, in particular the
massive and seemingly authoritative World War I ones, appeared to confirm racial and ethnic
stereotypes of the hereditary superiority of Nordic peoples over Slaves and South Europeans and
provided a strong impetus to the eugenics and immigration restriction movements. These two
subjects are discussed in the files of Charles B. Davenport, Charles W. Eliot, Samuel F. Fels, Henry
H. Goddard, Charles W. Gould, Walter Lippmann, Herbert A. Miller, Helen C. Putnam, Gino
Speranza, Victor C. Vaughan, Robert Ward (folder 961) and Leon F. Whitney.
For some twenty-five years, from 1922 to 1947, Robert M. Yerkes served as chair of the National
Research Council's Committee for Research in Problems of Sex. The greater part of the material
concerning the work of the committee can be found in Series II, Boxes 77-79, but additional
information is scattered throughout PROFESSIONAL CORRESPONDENCE, in the files for such
people as Sophie D. Aberle, Edgar Allen, Chester I. Barnard, Walter B. Cannon, George W. Corner,
Gilbert Van Tassel Hamilton, Ruth Hershberger, Alfred C. Kinsey, Frank R. Lillie, Amram
Scheinfeld, Lewis M. Terman, and Earl F. Zinn. The best known works sponsored by the
Committee are Alfred C. Kinsey's Sexual Behavior in the Human Male (1948) and Sexual Behavior in the Human Female (1953). The first controversial work is discussed in the correspondence of Yerkes with Barnard, Corner, Hamilton, Kinsey, and Terman.
Prior to his interest in intelligence testing and anthropoid apes, Yerkes published extensively on his
research into the behavior of lower animals, including the earthworm, fiddler crab, crawfish, frog,
rat, and ring-dove. He also published one book, The Dancing Mouse, in 1907. See Series IV,
WRITINGS, for copies of published books and articles. Yerkes discussed these and other similar
research topics with such professional colleagues as J. W. Baird, Lawrence W. Cole, Wallace Craig,
Philip B. Hadley, Charles S. Minot, Raymond Pearl, R. Myron Strong, Francis B. Sumner, and John
B. Watson. The correspondence of these men and other scholars portray efforts to make psychology
an experimental science, a discipline Yerkes often called psychobiology.
Like many others of his generation, Yerkes was involved in the effort to establish psychology as a
discipline. He was active, therefore, in the American Psychological Association, served on the
editorial boards of several psychology journals, and was interested in the nature of the field of
psychology. A great deal of material on these related subjects can be found in Series II, especially
in the files for the American Psychological Association, Boxes 56-57; Editor of Journals and Series,
Boxes 61-63; and Psychological Corporation, Boxes 83-84. Additional information can be found in
the folders for such people as Walter V. Bingham, Milton J. Greenman, Francis H. Herrick, Walter
S. Hunter, E.B. Titchener, Howard C. Warren, Margaret F. Washburn, and John B. Watson. Yerkes
was also concerned with promoting the professional careers of former students, research assistants
and younger colleagues. See for examples the files for Clarence Ray Carpenter, George M.
Haslerud, and Kenneth W. Spence. As Haslerud stated in a 1945 letter, "you have not only helped
me get out of this blind alley . . . but have helped me get much more confidence in my ability." The
letters between Yerkes and Donald K. Adams and Harold C. Bingham, together with related
correspondence in the files of Edwin G. Boring and Raymond Dodge, highlight the career
difficulties of scholars in the 1920's who were not of independent means.
Researchers can also find information in Series I on Yerkes' politics. He can, perhaps, be accurately
described as a liberal Democrat, but was never strongly engaged in political activity. Information on
his political views can be gleaned from the files for Burton E. Eames, Charles W. Eliot, Raymond
F. Fosdick, Ernest R. Hilgard, Walter Lippmann, Lucius E. Marple, Franklin Delano Roosevelt,
Fillmore H. Sanford, Harlow Shapley, Harry S. Truman, Henry A. Wallace, and in letters to Drew
Pearson and John P. Peters (folder 722). Further material on this subject is in Series II in the subject
files for Causes, Box 59; and Organizations, Boxes 80-82. Yerkes knew and corresponded with
such eminent Russian scientists as Nadie Kohts, Ivan P. Pavlov, and Alexandre P. Sellheim and
travelled to the Soviet Union in 1929 in search of information about Soviet primate research. (See
also the section Experiment Stations, Box 69, folders 1188 and 1195.) Due, therefore, to
considerations of personal friendship and a wish to perhaps return to Russia, Yerkes was publicly
"sympathetic with the experiment" and equally sympathetic of "socialistic ideals." See the
correspondence of Yerkes with George S. Counts and W. Horsley Gantt. In private, however, in a
confidential June 30, 1929 letter to his brother William Augustus Yerkes, he was much more
candid, stating that to "Leave Russia is somewhat like escaping from a prison camp" and that
"grosser injustice and inhumanity would be difficult to imagine." (Box 168, folder 2639).
The collection contains useful information on a wide variety of additional subjects. Reflections
upon aging, retirement, and life in general, for example, can be discovered in the correspondence of
personal friends and colleagues who through the years became close friends. There are, perhaps, a
couple of dozen such people, including Peter Frandsen, Lucius E. Marple, Herbert W. Rand, R.
Myron Strong, and Lewis M. Terman, Insight can be gained into conditions at Boston Psychopathic
Hospital under the directorship of E.E. Southard by reading the files for Elizabeth Chapman,
Frederick Gay, and Elmer Ernest Southard. (See also the folder for Boston Psychopathic Hospital in
Series II, Box 80, folder 1532.) The dim view that Yerkes held toward the Roman Catholic Church
can be seen in correspondence with Paul Blanshard, Henry P. Van Dusen (folder 953), and Harry S.
Truman (Box 59, folder 1133). In 1952 Yerkes read and was fascinated by Herbert J. Muller's The
Uses of the Past, a heavily annotated copy of which is found in Series IV, Box 126. He discussed
the book in letters to Muller (folder 612) and old friends like Richard M. Elliott, C. Judson Herrick,
and Lewis M. Terman.
Another way of looking at the PROFESSIONAL CORRESPONDENCE in Series I is by
identifying the kinds of people with whom he corresponded. Any division is somewhat arbitrary,
but some of the major types of correspondents are professional colleagues of Yerkes' generation,
younger psychologists, associates at Harvard and Yale, foreign scientists, personal friends, former
students and research assistants, possible benefactors and officials of private funding agencies,
chimpanzee and gorilla enthusiasts, naturalists and zoologists, and Yerkes' own professors.
Professional colleagues of the Yerkes generation, many of whom were pioneers in the field of
psychology, include James R. Angell, Walter V. Bingham, Edwin G. Boring, Carl C. Brigham, C.
Judson Herrick, Walter S. Hunter, Raymond Pearl, Lewis M. Terman, Edward L. Thorndike, E.B.
Titchener, Margaret F. Washburn, and John B. Watson. Younger professional colleagues include
such figures as Gordon W. Allport, Leonard Carmichael, Harold J. Coolidge, Jr., George W.
Corner, Richard M. Elliott and Alfred C. Kinsey. Among Professor Yerkes' associates at Harvard
University, Boston Psychopathic Hospital, Yale University, and the Yerkes Laboratories are such
people as Roswell P. Angier, Walter B. Cannon, Raymond Dodge, John F. Fulton, Arnold Gesell,
Earnest A. Hooten, Clark L. Hull, Karl S. Lashley, Walter R. Miles, Henry W. Nissen, Ralph
Barton Perry, Sidney L. Pressey, Herbert W. Rand, and E.E. Southard.
Yerkes corresponded with foreign scientists like Maurice Delorme, Julian Huxley, Wolfgang
Koehler, Nadie Kohts, Ivan P. Pavlov, Margaretha Selenka, Niko Tinbergen, and Hans Weinert,
primarily concerning primate research. Numbered among the many personal friends of the Yerkes
family are Burton E. Eames, Louisa Eyre, Peter Frandsen, T. Harry Haines, Gilbert Van Tassel
Hamilton, Lucius E. Marple, Arthur F. Perry, Jr., Ralph H. Spangler, R. Myron Strong, and Charles
F. Whiting. The series also contains the correspondence of many former student and research
assistants, including Donald K. Adams, Meredith P. Crawford, James H. Elder, Louis W.
Gellerman, Donald Hebb, Margaret Child Lewis, Vincent Nowlis, Austin H. Riesen, Kenneth W.
Spence, and Joseph G. Yoshioka. In his search for financial support for his anthropoid experiment
station, Yerkes corresponded with many officers of private foundations and with possible
benefactors, such as Chester I. Bernard, Edwin R. Embree, Abraham Flexner, Charles W. Gould,
Alan Gregg, William S. Learned, John C. Merriam, Robert S. Morison, Edward W. Scripps, and
George E. Vincent. Yerkes also corresponded with people who were enamoured with chimpanzees
and gorillas, like Benjamin Burbridge, Martin Johnson, Cathy Hayes, Keith Hayes, Mrs. Robert
Noell, and Richard D. Sparks. Sparks expressed the sentiments of all in a 1939 letter, when he
asserted, "gorillas, with me, are like liquor with an addict." A common interest in anthropoid apes
prompted Yerkes to correspond with many naturalists and zoologists, including Carl E. Akeley,
Mary L. Jobe Akeley, W.C. Allee, Frank M. Chapman, William T. Hornaday, Herbert S. Jennings,
Lorus J. Milne, William E. Ritter, and Clark Wissler.
The series contains some correspondence with Charles B. Davenport, William James, Hugo
Münsterberg, George H. Palmer, George H. Parker, and Josiah Royce, Yerkes' professors at
Harvard University. In the period before World War I, it was not uncommon for Americans to
pursue graduate studies abroad, particularly in Germany. The files contain letters written from
Germany by Charles Scott Berry, Frederick S. Breed, Harold C. Brown, Richard M. Elliott, and
John E. Rouse. As might be expected, Series I also includes correspondence on a variety of other
subjects. For example, the papers contain a 1937 letter from Yerkes to Thurman Arnold, giving his
reaction to The Folklore of Capitalism and a four page answer from the author. Scotland G.
Highland wrote Yerkes in 1945 asking about bloodsucking by war prisoners to satisfy thirst, while a
small folder for Fritz M. Urban gives an interesting account of the trials of a Czech psychologist
during Nazi occupation.
The correspondence in Series I, therefore, provides extensive documentation on the growth and
development of psychology as seen through the lives and careers of scores of scholars and
researchers and gives a great deal of information about the life, career, and interests of Robert
Mearns Yerkes. Researchers wanting to study the subjects discussed above must remember,
however, that the examples cited are by no means inclusive or exhaustive. They are listed to give
direction to scholars and provide information on some of the major subject areas covered in the
Series II, SUBJECT FILES, fills Boxes 55-113. The SUBJECT FILES consist of correspondence,
plus reports, memoranda and proposals, minutes of meetings, and other similar papers arranged
alphabetically by broad subject area in accordance with the organizational system established by
Helen S. Morford. The major subject areas are similar to those in Series I, except that the papers are
arranged by subject instead of by correspondent.
Those interested in primate research should examine the files under the subjects of Anthropoid
Research, Chimpanzees, Experiment Stations, Gorillas, Gorilla Studies, Works by Yerkes, Yerkes
Laboratories of Primate Biology, and Zoos.
The subject of intelligence testing is treated in several parts of Series II, most important being in the
section, War: World War I, Psychological Examining in the U.S. Army. Additional material is to be
found under the headings for National Research Council, Box 76, folders 1446-1448; Research:
Test materials, Box 87; and Works by Yerkes, Boxes 96 and 98-99. The subject of immigration
restriction is discussed in the files for National Research Council: Committee on Scientific
Problems of Human Migration. Yerkes served as chair of this committee from 1922 to 1925. For
material on the subject of eugenics, see Causes: Eugenics, Committees, and Organizations. Among
the several committees and organizations concerned with eugenics which Yerkes was associated
with are the American Breeders' Association, Eugenics Research Association, American Eugenics
Society, Massachusetts Society for Mental Hygiene, and the National Committee for Mental
Hygiene. Of related interest was population control. See the folders for Planned Parenthood
Federation of American and Population Association of America under the heading for
Series II also includes material useful for documenting the other research interests of Yerkes. See
the headings for Research and Works by Yerkes.
Robert M. Yerkes was one of the most distinguished psychologists of his era. It is not surprising,
therefore, to find extensive files that document his interest and stature in his field, the most
important being American Psychological Association, Committees, Conferences, Congresses, Fels
(Samuel) Research Institute, Intersociety Constitutional Convention, National Research Council,
Organizations, Psychological Corporation, and Society of Experimental Psychologists. Due to his
prominence, he also belonged to and was active in several learned societies, like the American
Academy of Arts and Sciences, American Association for the Advancement of Science, American
Philosophical Society, and the National Academy of Sciences. The section Editor of Journals and
Series is also relevant in this regard.
Information on Yerkes' politics is located in two sections of Series II - Causes and Organizations.
Information about Yerkes' institutional affiliations and teaching can also be found in Series II. See
the files under the headings for Harvard University, Johns Hopkins University, University of
Minnesota, Teaching, Ursinus College, and Yale University. The University of Minnesota and
Johns Hopkins University files are particularly interesting. By 1916, Yerkes, still an assistant
professor, felt that his career at Harvard was at a standstill and he began searching for a new
position. The University of Minnesota in the spring of 1916, which was in the process of separating
psychology from philosophy, offered Yerkes the position of chair of the new psychology
department together with the post of director of the psychological laboratory at the rank of full
professor. Yerkes declined the offer, but it was renewed in 1917 and he accepted. The war,
however, intervened and afterwards Yerkes became employed by the National Research Council.
He resigned a position that he never filled in March 1919. The next year he negotiated
unsuccessfully with Johns Hopkins University in the hope of developing psychobiological and
anthropoid research there. Not until 1924 did he find a university position that would allow him to
pursue primate studies, negotiations found in Series I in the correspondence of James R. Angell and
Roswell P. Angier.
Two other major subjects are covered in Series II. Correspondence, reports, and articles on
psychology in World War II are found in Boxes 94-96. Information on the extensive publishing
activities of Yerkes is located in the sections Periodicals, Publishers, Reprints and Reproducing,
Research, and Works by Yerkes. What is found in Series II, however, is primarily correspondence
about his research and publications, not copies of the publications. For copies of his publications,
see Series IV, WRITINGS.
Series III, EXPERIMENTS, is contained in Boxes 114-120 of the Robert M. Yerkes Papers. It
consists of notebooks of observations on chimpanzees and the gorilla Congo, notes on experiments
with chimpanzees, and a laboratory log covering the period 1925-1942. These materials are housed
in Boxes 114-117 and 120. A variety of other materials is found from the end of Box 117 through
Box 119, including announcements for Yale's Institute of Psychology, pro-seminar syllabi, and
several bound typescripts. One of the bound typescripts is The Biojonnismith, a publication
"containing short tales for the juvenile mind," edited and produced by Yerkes, R. Myron Strong,
Helen Makepeace, C.A. Holbrook, and Ada Watterson at Woods Hole in 1900-1901. The other
bound typescripts date from the first decade of the twentieth century and consist of pseudonymous
manuscripts written under the names C.J. Blix and Romby.
Series IV consists of WRITINGS and is divided into two sections. The first section, Books, is
housed in Boxes 121-127 and the second section, Papers, is in Boxes 127-130. WRITINGS contain
copies of books, articles, and reviews of Robert M. and Ada Watterson Yerkes, plus a handful of
related materials by others. Books has copies of such major publications as The Dancing Mouse
(1907), A Point Scale of Measuring Mental Ability (1915) with James W. Bridges and Rose S.
Hardwick, Psychological Examining in the United States Arm (1921), Almost Human (1925), The Mind of a Gorilla (1926-1928), and The Great Apes (1929). Also included is John Dewey's Psychology, third revised edition 1893, about which Yerkes states, "this little books gave me my introduction to psychology as science," The Uses of the Past (1952) by Herbert J. Muller, and several other items. The section on Papers has nine bound volumes of articles and reviews by Robert M. Yerkes and Ada Watterson Yerkes published between 1899 and 1956, plus a binder
containing publications too large to be included in the bound papers, publications about Yerkes
including biographical memoirs, and items printed after his death. Each bound volume contains an
index to all items included within the volume. A complete listing to all the publications of Robert
M. and Ada Watterson Yerkes is found in Box 130, folder 2235.
The Robert M. Yerkes Papers contains fifteen boxes of photographs and these make up Series V.
PHOTOGRAPHS. Boxes 131-136 house professional photographs and they consist primarily of
albums of chimpanzee and gorilla pictures plus book illustrations and World War I photos. Personal
photographs are contained in Boxes 137-145 and also largely consist of albums. Most of the
pictures were taken by Ada Watterson Yerkes and Roberts Yerkes Blanshard, virtually all pictures
are clearly identified, and the albums contain contents listings.
The final series, PERSONAL PAPERS, fills Boxes 146-177. The material is arranged under broad
headings, the most important being Autobiographical, Biographical, Family, Family: Relatives, and
The Autobiographical section, located in Box 146, folders 2311-2319, contains a typescript of
Robert M. Yerkes "Testament," a document that is both an autobiography and a statement of his
belief in the efficacy of science. A microfilm copy of the "Testament" is available as HM Film 133.
The Biographical section, Boxes 146-157, contains biographical memoirs and obituaries,
reminiscences, school memorabilia, college and graduate school materials, honorary degrees,
address books, a report on the 1976 Yerkes Centennial Conference, and a variety of similar
materials. Under the heading for Family, Boxes 159-165, one finds correspondence, biographical
material, writings, research notes, and miscellanea on Ada Watterson Yerkes; correspondence of
son David Norton Yerkes and his wife and daughter; letters of Robert M. Yerkes to his wife Ada,
son David, and daughter Roberta; and correspondence of Roberta Watterson Yerkes Blanshard.
Family: Relatives, Boxes 165-168, contains letters to and from Carrell, Diebitsch, Hughes, Krusen,
Mearns, Norton, Watterson, and Yerkes relatives together with letters of members of the immediate
family of Robert N. Yerkes, his parents Susanna Addis Carrell and Silas Marshall Yerkes and
younger brothers Miles and William Augustus Yerkes. The final section, Diaries, is housed in
Boxes 169-177. Robert M. Yerkes began keeping a diary in 1893, a practice he faithfully continued
to 1906. The collection contains five diaries covering some of the years between 1908 and 1920 and
a final series of diaries covering the period 1940-1954. In addition there are lists of and annotations
for books read between 1891 and 1893, a daily record of his anthropoid research at the Abreu
plantation in 1924, a log and notes from his 1929 European and African journey, five diaries of Ada
Watterson Yerkes, a date book, and record of household accounts for the period 1905-1912.
Researchers can find information in Series VI on the research and professional interests of Professor
Yerkes. Those interested in the subject of anthropoid research should examine family
correspondence, particularly letters from Robert M. Yerkes to his wife, Boxes 163-164; letters to
other family members; the "Testament," Box 146; writings and notes of Ada Watterson Yerkes,
Box 161; and his 1924 notes taken at the plantation of Madame Rosalia Abreu, Box 172, folder
2666. Yerkes' World War I military experiences in psychological testing can likewise be traced
through the "Testament," correspondence with his wife, and his 1917-1918 war journal, Box 171,
PERSONAL PAPERS contain a great deal of material documenting the educational growth of
Robert M. Yerkes at West Chester State Normal School, Ursinus College, and Harvard University.
The diaries of Yerkes, Boxes 169-170, are especially useful in this context. The documentation for
his years at Ursinus College and Harvard University, Boxes 147-155, is particularly rich. Yerkes'
Ursinus College years, 1893-1897, are represented by course grades, papers, notebooks, essays and
exercises, exams, and a variety of printed materials. For further information on his devotion to
Ursinus, see the small section for Ursinus College in Series II, Box 91, folders 1739-1742. The
Harvard University material, 1897-1902, includes bills, grades, exams, fellowships, etc. plus an
extensive collection of philosophy, psychology, and zoology notebooks and papers. The diaries and
the Woods Hole files, Boxes 155-156, folders 2436-2344, provide a useful record of his early
The Real Estate section and correspondence in the Family sections have material on the Franklin,
New Hampshire farm owned by Yerkes. Purchased in 1911, the farm served as a family retreat and
site for early chimpanzee research. Additional information about the Franklin property is scattered
throughout Series I. See, for example, the files for Walter B. Cannon, Burton E. Eames, Louisa
Eyre, and Lee Russell.
The sections devoted to Family and Family: Relatives are housed in Boxes 159-168. They consist
primarily of correspondence and all of it to, from, and about Yerkes and Watterson relatives, except
for four folders of correspondence of Ada Watterson Yerkes with friends, one of whom, Elizabeth
Cutter Morrow, was the mother of Anne Morrow Lindbergh. Although the collection contains a
great deal of correspondence between Robert and Ada Yerkes, Boxes 159 and 163-164, few letters
date from the period before their September 1905 marriage. Most of these letters were destroyed by
The family correspondence and diaries, supplemented by the "Testament," give information about a
wide variety of domestic topics. The letters between husband and wife reveal the deep feelings of
love and respect they had for each other and also the sense that their marriage was a true
partnership. Ada Watterson Yerkes authored or coauthored ten articles, four of which concerned
primates, and also coauthored The Great Apes: A Study of Anthropoid Life (1929). Yerkes enjoyed
warm relationships with his children, two brothers, many cousins, uncles and aunts, and his mother,
who died of cancer in 1913, but he was not close to his father, Silas M. Yerkes. Father and son
disagreed on the relative importance of education and farm work, a situation made more difficult by
financial problems caused by a fire that destroyed the Yerkes farm in 1893. From these same
sources researchers can also find useful material about farm life and rural conditions in Bucks
County, Pennsylvania at the end of the nineteenth century and about youthful activities and college
life. After retirement Yerkes became increasingly interested in family history and delighted in
recalling the events of his youth, thus readers interested in these subjects should examine the "round
robin" letters to his brothers Miles and William Augustus Yerkes in Boxes 167-168. See also Box
147, folders 2329-2334 for additional material on life in Bucks County in the late nineteenth
The final Oversize section contains a sound recording of vocalization of baby gorillas, a microfilm
copy of correspondence between Yerkes and E.B. Titchener found at Cornell University, one trunk
of World War I era psychological testing materials, and a roll of charts on psychological examining
in World War I.
Those seeking additional background information on Robert M. Yerkes should consult his
Testament, Box 146, folders 2311-2317 and Memoirs, Box 146, folder 2323. The biographical memoirs written by Edwin G. Boring for the Year Book of the American Philosophical Society,1956 and Ernest R. Hilgard for the National Academy of Sciences in 1965 are particularly good.
The latter essay has a twenty-four page biographical sketch, chronology, and bibliography of the
publications of Robert M. Yerkes.