“GHOST” HARRY: You’re juggling too many people, Dexter.

DEXTER: I know. Arthur, Beaudry, Rita, now Batista . . .

“GHOST” HARRY: I’m not talking about them. I mean Dexter Morgan. Blood tech. Husband. Father. Serial killer. And now Kyle Butler, extortionist? Which one are you?

DEXTER (looking into multiple mirrors): All of them.

—“Hello, Dexter Morgan,” 4-11

Issues of self and identity have historically ranked among the most beguiling and bemusing of the topics studied by psychologists and philosophers. Self is such a tricky concept in part because it is so broadly used. Even a cursory peek at the psychological research literature reveals dozens of theories and concepts that employ the term: self-esteem, self-concept, self-discrepancy, self-regulation, self-awareness, etc. There are also everyday uses of the term: we often speak of “feeling self-conscious” or “acting selfishly.” In modern psychology, self is often defined as the mental apparatus that permits individuals to experience abstract, inwardly directed thoughts and feelings. Research in comparative psychology reveals that some non-human animals, including chimpanzees, gorillas, elephants, dolphins, parrots, and cephalopods (octopi and squid), have a demonstrable ability to recognize themselves. The fact that selfhood, like the lens-bearing eye, has independently emerged in numerous distinct evolutionary lineages suggests that it is very useful feature. It is also notable that the species with self-recognition abilities tend to be, like humans, highly social. However, it has typically been argued that such non-human selfhood is fairly rudimentary: the complex reflective self is thought to be unique to human beings, and core to our  …