4 MISC. PUBLICATION 86, U. S. DEPT. OF AGRICULTURE 
of environment in the evolution and life of mammals is unknown. 
The numerous significant and interesting studies in genetics and 
heredity seem to have resulted in an unwarranted emphasis on the 
power of heredity, often at the expense of environment. It is proba- 
ble that field biologists, though conceding at once the enormous im- 
oe of heredity, generally are in agreement with Jennings 
(95) p40) 
Any characteristic requires for its production both an adequate stock of 
chemicals and an environment adequate for its production through proper 
interaction of these chemicals with one another and with other things. In 
these senses all characteristics are hereditary and all are environmental, but 
no characteristic is exclusively hereditary or exclusively environmental. 
and (9, p. 57-58)— 
Heredity is stressed as all powerful; environment as almost powerless; a 
vicious fallacy, not supported by the results of investigation. 
It is clear that the study of the relation of the environment to the 
development, structure, and habits of the living form is as weil 
worthy of critical and prolonged attention as that which has been 
given to heredity in the past few decades. Results obtained from 
experiments with plants by Clements, MacDougal, Hall, Garner, 
and others are extremely suggestive of lines of activity that should 
be carried on with mammals and other animals, as well as with 
plants. For complete success such investigations are dependent not 
only on critical experimental treatment, but also on extensive and 
careful field surveys and life-history studies of the forms considered. 
Studies of environment and its influence on mammals and on ver- 
tebrates generally have no more than been begun but promise much 
for the future of biological science. Investigations in this province 
depend primarily on critical observation and analysis of hfe 
histories. 
INFLUENCES ON ENVIRONMENT 
~The environment not only influences the mammal, but the mammal 
influences its environment through its multitudinous activities, as 
in loosening soil by burrowing and in excavating dens, burying 
rocks, packing soil by tramping and trail making, collecting mate- 
rials for nests, building dams and flooding valleys, and scattering 
and planting seeds or destroying seeds and vegetation. Incorpora- 
tion in the soil of organic materials, such as skin, bones, flesh, and 
excreta, also may be included in these activities. Of course, the 
influence of one or of a few mammals ordinarily counts for little, 
but when the aggregate work of thousands and even millions of 
individuals is taken into account the effects on environment are 
without doubt, in many instances, of great importance. The soil- 
building and fertilizing, or even the soil-destroying, role of different 
burrowing and terrestrial mammals remains to be determined. 
Christy (4), Bell (2), and Grinnell (7, p. 745) have already drawn 
attention to the significant parallel between the pocket gopher of 
North America and the earthworm in England, as regards their 
work in soil formation. Studies of this and related subjects should 
be carried forward on a much broader scale than heretofore. It is 
inevitable, in the study of life habits, that effects of mammals oa 
their surroundings should assume a prominent place. 
