MCGEE] UNIFORMITY OF HUMAN DEVELOPMENT 827 
of the experiential basis of mathematics was recently afforded by the 
president of the American Mathematical Society.' 
2. In all departments of definite knowledge, but especially in the sev- 
eral branches of anthropology, it is implicitly, if not explicitly, postul- 
ated that knowledge is diffused and its acquisition stimulated through 
association and interchange among individuals and peoples; indeed, 
this postulate affords the warrant, and forms the basis, for education. 
3. In anthropology as in other sciences it is necessary to recognize 
a volume or body of knowledge proper to each people, made up of the 
combined intellectual possessions of all the individuals, increasing with 
successive experiences, decreasing only through disuse or neglect, and 
in greater part perpetuated by record and tradition if not by direct 
heritage. 
4. In ethnologic research, as measurably in other lines of inquiry, 
it is desirable and fair to assume that (7) mental capacity and (4) the 
sum of knowledge, either in the individual or in the group, are in the 
long run practically equivalent. 
5. In ethnologic inquiry it is convenient to assume that the course of 
development is approximately uniform (or about as nearly similar as 
are environmental conditions) in each separate or independent group 
of men. This assumption, which was recognized first by Powell under 
the law of activital similarities, and later by Brinton under the formula 
“unity of mind,” is rapidly crystallizing in the minds of anthropolo- 
gists; it is, indeed, but a corollary of the primary postulate on which 
all science rests, namely, that knowledge grows by natural means; and 
latterly the postulate (which is but a generalization of invariable experi- 
ence), with its corollaries and applications, has been formulated as one 
of the cardinal principles of science, namely, the responsivity of mind.? 
The recognition of the foregoing principles yields a means of out- 
lining intellectual development in general, and hence of defining the 
grades, or growth-stages, of given intellectual stocks (or peoples); for 
when once the general scheme of development indicated by the several 
examples is perceived clearly, the relative positions of each of the 
examples are evident. The relations of the natural stages in intellee- 
tual development may be illustrated by comparison with the growth- 
stages of aged sequoia groves of prehistoric birth, whose beginnings 
no man recorded and no living man saw, but whose history may be 
read clearly in terms of younger groves in other counties; for the 
towering groyes of the big-tree species and the upshooting forests of 
human ideas may well be likened in individual and collective growth, 
save that the vegetal species is decadent and shrunk into scattered 

1“Eyen pure mathematics, though long held apart from the other sciences, must be founded, I 
think, in the last analysis, on observation and experiment.’’—R. S. Woodward, Science, new ser., 
vol. x111, 1901, p. 522. 
2Proc. Washington Academy of Sciences, vol. 11, 1900, pp. 1-12. 
