In a footnote on p. 197 Sen writes, "A half-jocular, half-serious objection to the criteria of fairness of Rawls and others runs like this: Why confine oneself in the [original] position of other human beings only: why not other animals also? Is the biological line so sharply drawn? What this line of attack misses is the fact that Rawls is crystallizing an idea of fairness that our value system does seem to have, rather than constructing a rule of fairness in vacuum based on some notions of biological symmetry. Revolutions do take place demanding equitable treatment of human beings in a manner they do not demanding equality for animals. 'If I were in his shoes' is relevant to a moral argument in a manner that 'if I were in its paws' is not. Our ethical system may have had, as is sometimes claimed, a biological origin, but what is involved here is the use of these systems and not a manufacture of it on some kind of a biological logic. The jest half of the objection...