Via a post about the infection analogy for cultural evolution over at Language Log, Cosma Shalizi posts an excerpt from André Siegfried’s Germs and Ideas:
The spreading of germs and ideas
There is a striking parallel between the spreading of germs and the spreading of ideas or propaganda. On the one hand we are dealing with a virus which can be transported and transmitted under certain conditions which favor or limit its transportation or transmission: on the other hand with ideas, religions, and doctrines, which can be described as germs, benevolent or malevolent, according to the point of view one takes up. These germs can either remain at their source and be sterile, or emerge in the spreading of infection. The vocabulary which normally comes to mind is that of medicine. Conditions of infection, besides, will also be the same as in the domain of health. For diffusion to take place we must necessarily have a germ, a carrier, and receptive surroundings. It is then, as in the case of epidemics, a matter of contacts, made easier by the techniques of communication or delayed by obstacles arising from custom or from administration. Sociology and biology are curiously akin in this.