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The Mental Life of Monkeys and Apes:
A Study of Ideational Behavior
ROBERT M. YERKES
Harvard University
BEHAVIOR MONOGRAPHS
Volume 3, Number 1, 1916
Serial Number 12
Edited by JOHN B. WATSON
The Johns Hopkins University
I. Interests, opportunity and materials
II. Observational problems and methods
III. Results of multiple-choice experiments:
1. Skirrl, Pithecus irus 2. Sobke, Pithecus rhesus 3. Julius, Pongo pygmaeus
IV. Results of supplementary tests of ideational behavior:
1. Julius, Pongo pygmaeus:
Box stacking experiment
Box and pole experiment
Draw-in experiment
Lock and key test
2. Skirrl, Pithecus irus:
Box stacking experiment
Box and pole experiment
Draw-in experiment
Hammer and nail test
Other activities
3. Sobke, Pithecus rhesus:
Box stacking experiment
Draw-in experiment
Box and pole experiment
Other activities
V. Miscellaneous observations:
1. Right- and left-handedness
2. Instinct and emotion:
Maternal instinct
Fear
Sympathy
VI. Historical and critical discussion of ideational behavior in
monkeys and apes:
1. Evidences of ideation in monkeys
2. Evidences of ideation in apes
VII. Provision for the study of the primates and especially the monkeys
and anthropoid apes
VIII. Bibliography
Two strong interests come to expression in this report: the one in thestudy of the adaptive or ideational behavior of the monkeys and theapes; and the other in adequate and permanent provision for the thoroughstudy of all aspects of the lives of these animals. The values of theseinterests and of the tasks which they have led me to undertake are sowidely recognized by biologists that I need not pause to justify ordefine them. I shall, instead, attempt to make a contribution of fact onthe score of each interest.
While recognizing that the task of prospecting for an anthropoid orprimate station may in its outcome prove incomparably more important forthe biological and sociological sciences and for human welfare than myexperimental study of ideational behavior, I give the latter first placein this report, reserving for the concluding section an account of thesituation regarding our knowledge of the monkeys, apes, and otherprimates, and a description of a plan and program for the thorough-goingand long continued study of these organisms in a permanent station orresearch institute.
In 1915, a long desired opportunity came to me to devote myselfundividedly to tasks which I have designated above as "prospecting" foran anthropoid station and experimenting with monkeys and apes. First ofall, the interruption of my academic duties