A familiar phenomenon in the history of science is the transference of a concept from one field of investigation to another. At present the newer concepts in use in physics are being applied in the social sciences. The classic example of this transference phenomenon is the concept of evolution; originating in the social sciences, it was taken over into biology and thence to the whole range of current thought. This paper aims at tracing the use of one idea--the struggle for (...) existence--by Malthus in 1798 in an attempt to solve a problem in economics and politics, its elaboration by Darwin sixty years later into the theory of natural selection for the purpose of solving a problem in biology, and the immediate application of the combined doctrines by Walter Bagehot in an effort to solve the problem of social change. (shrink)