 Together with the observation recorded earlier—that speakers do not usually seem to be able to formulate semantic rules or to cite them as reasons—some philosophers have looked for alternative ways of understanding the explanatory power of meaning determining rules, for instance in terms of evolution. Ideas here range from using evolutionary explanation as a mere analogy (as in Sellars 1954 or Searle  1995)[37]  to normative construals of the idea of a biological function in normative teleosemantics (cf., e.g., Jarvis 2012), possibly in combination with computational ideas about sub-personal rule following at the level of mental representation (cf. Jacob 2005: 200f; García-Carpintero 2012; for some critical discussion Boghossian 2008). There is a worry, though, that the basic question recurs: What distinguishes a sub-personal regularity from a performance governed by a sub-personal  rule?[38]