ABSTRACT
The idea of cultural evolution resembling biological evolution has a long history. For example, William James (1880) published an essay drawing parallels between cultural evolution and biological evolution. More recently, Cloak (1973, 1975) has formally examined the general evolution of elementary self-replicating instructions as phenomena of both neural memory and the molecular memory of nucleic acids. His analysis uses a very broad definition of the word “instruction” that includes all neural structures that regularly respond to a characteristic cue with a characteristic behavior. By analogy to the way many computer instructions may constitute computer software, many neurally stored instructions (in Cloak's broad sense) may constitute mental software. 1 In a term that is perhaps more self-explanatory, as well as more general in some ways and more specific in other ways, I have used the term thought contagion to refer to self-propagating ideas. Inasmuch as any idea can play at least a passive role in self-propagation by merely existing in someone's brain, a more formal definition may be based on whether the idea has actually resulted in self-propagation. In its formal, broad sense, the term thought contagion therefore denotes the following: a memory item, or portion of an individual's neurally stored information, whose causation depended critically upon prior instantiation of the same memory item in one or more other individuals. 2 The study of thought contagions has numerous implications, some of which pertain to the evolution of intelligence. Specifically, it pertains to the evolution of the collective intelligence of populations and the individual intelligence of humans.
