The second premise asserts that exercise of reason is both the key structural property of human life and the realization of the fully developed human form

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