I shall argue that the function of the reproductive capacity is not to perpetuate the kind (or species), but to allow the individual reproducer to be eternal: not eternal without qualifications, but in a way. The basic premise in the arguments which establish this conclusion distinguishes between things which are numerically eternal and those which are formally eternal. This of this latter sort must be members of an everlasting series of individuals which are one-in-form (ἕν εἴδει, in Aristotle's usage). The full understanding of these passages, therefore, requires a proper interpretation of the distinction between numerical and formal unity. with this distinction clarified, and with a better understanding of Aristotle's teleological explanations of reproduction and sex, i close by suggesting another 'function' of reproduction - eliminating forms as independent paradigms for natural substances.
Lennox, James G., "Aristotle and the Functions of Reproduction" (1982). The Society for Ancient Greek Philosophy Newsletter. 316.