Levine and Heller open by establishing that adult romantic bonding operates on the same underlying biological attachment system that governs infant-caregiver bonding.

Why this framing matters:

• Adult attachment isn't a separate, purely psychological phenomenon layered on top of romance — it's the same evolved system, repurposed
• This explains why relationship security or insecurity feels so viscerally significant, not merely intellectual
• Attachment styles formed early tend to persist, though they can shift with corrective relational experience

This grounding in attachment biology sets up the book's central framework of three attachment styles explored in subsequent chapters.