Not every method of creating human-level intelligence is an extendible method. For example, the currently standard method of creating human-level intelligence is biological reproduction. But biological reproduction is not obviously extendible. If we have better sex, for example, it does not follow that our babies will be geniuses.

David Chalmers, ‘The Singularity: A Philosophical Analaysis’, Journal of Consciousness Studies, vol. 17, nos. 9-10 (2010), p. 18