Attachment theory, as originally outlined by Bowlby (1973, 1980, 1969/1982), suggests that the ways people think, feel, and behave in close relationships are shaped by the dynamic interplay between their genes and their social environment. Research on adult attachment, however, has largely focused on the latter, providing only a partial picture of how attachment styles emerge and develop throughout life. The present research leveraged data from the Minnesota Twin Registry, a large sample of older adult twins (