   Griffiths (2001) distinguishes between two ways to conceive of information, causal and intentional, and then argues that under either conception, information is not restricted to DNA. Causal theories of information, based on Dretske's (1981), are related to the Shannon mathematical theory of information (1948). Dretske distinguishes between a source variable and background or channel conditions. On Griffiths' (2001) reading of Dretske's theory, a source variable, X, carries information about variable Y if the value of X is correlated with the value of Y. Griffiths describes the causal interpretation of this idea as follows: