The Echo Maker explores the idea that identity changes over time in response to one’s environment and relationships. Mark’s experience of Capgras syndrome doesn’t take place in isolation from the people around him. He forces other people, especially Karin and Weber, to change their own identities in reaction to him.

Mark, Karin, and Weber all dramatize the search for a stable sense of self in different ways. Mark’s sense of self is exactly as it has always been, but his perception of the world has changed drastically. Over time, Mark begins to doubt whether his image of himself is really the same as he remembers, and only then is he willing to entertain the possibility that his perception of external reality may be at fault. Karin has built a large part of her identity around being a big sister while Weber’s identity changes when he is at home with Sylvie, on a television set, or face to face with Mark.

Mark’s Capgras syndrome severs his emotional connection to the people and things closest to him—his sister, his dog, and his home. Since those are the three things closest to his sense of self, he has effectively lost the greater part of his identity.