Carter Dillard (Visiting Scholar, Vulnerability and Human Condition Initiative, Feminism and Legal Theory Project, Emory University School of Law) has posted
Empathy with Animals: A Litmus Test for Legal Personhood? (Animal Law Review, Vol. 19, 2012) on SSRN. Here is the abstract:
Is there any relationship between the disposition of some humans to empathize with and respond to the interests of nonhuman animals, and the criteria we ought to use for determining who becomes a legal person? This brief essay argues that there is, by employing a thick conception of legal personhood, and suggests that criteria be used to determine who constitutes our legality in the future.