Source status: ordinary and psychological term, not a single settled mechanism.
Identity is the changing sense of who a person understands themselves to be across roles, relationships, memory, values, body and culture.
The journeys do not assume a pure self exists underneath every adaptation. They ask which qualities remain alive by choice, which roles have become compulsory and what becomes possible when identity has more room.
Different from: adaptation. Adaptation is one way a person changes in response to context. Identity is the larger, ongoing experience those adaptations may enter.