ABSTRACT
Ifwe ask 'What does a cat have sharp, curved claws for?' and answer simply 'To catch mice with', this does not imply a profession of any mythical teleology, but the plain statement that catching mice is the function whose survival value, by the process of natural selection, has bred cats with this particular form of claw. Unless selection is
at work, the question 'What for?' cannot receive an answer with any real meaning. (Konrad Lorenz 1966, 9)
The English word 'function' has many different senses. Two of these seem particularly prominent in the biosciences (Godfrey-Smith 1994; Griffiths 1994):
Selected function---e.g., a sequence of nucleotides GA U has the selected function of coding for aspartic acid if one reason that sequence evolved by natural selection was because it had the effect of inserting that amino acid into some polypeptide in ancestral organisms.
