While we have come to recognize clearly the fact of extinction of animal types and their replacement by other forms of life there appears to have been less attention to the special factors concerned in such extinction, or, to put it differently we have been devoting our attention especially to the factors concerned in the production of new types, the variation and evolution of animals, rather than the factors of extinction. It is true that these may bear a close relationship and present mutual dependencies and possibly we might take them as necessary corollaries or consider factors of extinction as merely negative factors of evolution, but it seems to me worthwhile to attempt a distinct formulation of those factors especially concerned in the elimination of life forms even if for no other purpose than to emphasize those factors of progressive evolution against which they contrast.
Proceedings of the Iowa Academy of Sciences
©1901 Iowa Academy of Science, Inc.
"Factors of Extinction,"
Proceedings of the Iowa Academy of Science, 9(1), 47-52.
Available at: https://scholarworks.uni.edu/pias/vol9/iss1/8