A Formal Model of Affiliative Interpersonality

Capturing the complexity of interpersonal dynamics—emerging from approach and avoidance motives of two individuals in dyadic interplay—remains challenging. In line with calls for embracing complexity in psychological research using formal modeling, we employed evolutionary game theory to investigate the underlying mechanisms of affiliative interpersonality. We constructed a relational state space that represents the ways of relating available in the momentary state of an interpersonal relationship. Next, we modeled relationships as trajectories in that relational space. Qualitatively different interpersonal dynamics emerged: (a) global stability with only one relational attractor (e.g., pure reciprocal friendliness), (b) bistability with two mutually exclusive attractors (e.g., either pure friendliness or pure distance), and (c) cycles between friendliness and distance in the relational space. The bistable dynamics appear to resemble the phenomenon of interpersonal complementarity (e.g., friendliness invites friendliness). Furthermore, the model generates psychopathologically relevant dynamics (e.g., oscillating, unstable interpersonal relationships in borderline personality disorder).