Personhood is a foundational concept in ethics, yet defining criteria have been elusive. In this article we summarize attempts to define personhood in psychological and neurological terms and conclude that none manage to be both specific and non-arbitrary. We propose that this is because the concept does not correspond to any real category of objects in the world. Rather, it is the product of an evolved brain system that develops innately and projects itself automatically and irrepressibly onto

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... the world whenever triggered by stimulus features such as a human-like face, body, or contingent patterns of behavior. We review the evidence for the existence of an autonomous person network in the brain and discuss its implications for the field of ethics and for the implicit morality of everyday behavior. We thank the members of our laboratory group at the Center for Cognitive Neuroscience for many fruitful discussions regarding personhood and the social brain, and an anonymous reviewer for helpful comments on this article. The writing of this article was supported by R21-DA01586, R01-HD043078, R01-DA18913 and a postdoctoral fellowship through T32-NS07413 at the Children's Hospital of Philadelphia. 1 Judeo-Christian theology offers a different perspective on personhood, emphasizing a person's relationships, including relationships with other persons and with God. According to this view, it is the participation in these relationships that endows an individual with personhood (Brown 2004). Although interpersonal relationships normally require rationality and many of the other psychological capacities to be discussed, this tradition also recognizes the relationships between humans who lack such capacities and persons who care for them.