- The mortal enemies of man are not his fellows of another continent or race; they are the aspects of the physical world which limit or challenge his control, the disease germs that attack him and his domesticated plants and animals, and the insects that carry many of these germs as well as working notable direct injury. This is not the age of man, however great his superiority in size and intelligence; it is literally the age of insects.
- The Social Life of Animals (1938), Chapter VII: Some Human Implications.
- Widely dispersed knowledge concerning the important role of basic cooperative processes among living beings may lead to the acceptance of cooperation as a guiding principle both in social theory and as a basis for human behavior. Such a development when it occurs will alter the course of human history.
- Cooperation among Animals with Human Implications (1951), page 213 (cited in "The Altruism Equation", by Lee Alan Dugatkin (2006), page 58).