 In the light of the discussion so far, it ought to be clear that, as it stands, the second premise of this argument is incompatible with the evolutionary biology of species. It asserts that the exercise of reason is not only the key structural property of human life, but also the realization of the fully developed human form. No sense can be made of this latter notion in evolutionary terms. Nevertheless, a series of prominent contemporary ethicists—Alasdair MacIntyre (1999), Rosalind Hursthouse (1999), Philippa Foot (2001) and Martha Nussbaum (2006)—have all made variants of the ergon argument central to their ethical theories. As each of these authors advance some version of the second premise, it is instructive to examine the ways in which they aim to avoid the challenge from evolutionary biology.