There is nothing which makes either of them are “you.” The feeling of Self is a useful predictor which a physical subsystem uses to nagivate the world and predict observations. “I” is not a physically real label which attaches the “you”-ness to physical systems, the physical systems simply are, and are inherently first-person in character. The only real you is the global quantum wave function, or whatever the underlying real stuff is doing.

Materialism directly implies no-self and Advaita Vedanta schools of thought.