Separation-individuation theory (Blos, 1967) and Erikson’s (1968) lifespan developmental theory claim that the developmental tasks of separation, identity and intimacy follow each other in a sequential order during adolescence and emerging adulthood. Using new conceptualizations and longitudinal research with adolescents aged 15 to 22 years, this research project prospectively tests the central hypotheses (phasing and conditionality) of this epigenetic principle.