Chapter XIV

THE INFLUENCE OF THE ENVIRONMENT AMONG ANIMALS AND PLANTS 325

(1) Observations show that environment and heredity are
complementary one to the other. (2) Abnormal stimuli may produce
almost any result, but (3) for each species there is a normal
environment, to certain elements in which marked responses may
be made, though (4) generally speaking sessile organisms are far
more responsive to differences in the environment than are
free-living organisms. (5) Among free-living species in a state
of nature closely related to man, modifications are not of great
importance in producing variations.

CHAPTER XV

THE INFLUENCE OF THE ENVIRONMENT UPON MAN 336

(1) Among men there is no normal environment. (2) The effect of
exercise, (3) of general conditions, (4) and of climate. (5)
Huntington’s theory of optimum climatic conditions. (6) The
effect of food, altitude, &c. (7) Statistical results. (8)
Effect of disease. (9) Evidence derived from twins. (10)
Conclusion that modifications, with the exception of those
produced by disease, are not of great importance, though of more
importance than in the case of species closely allied to man.