Evolution and relationships: The integration continues

In this commentary, I highlight the importance of conceptualizing research at the interface of evolution and relationships within Tinbergen's (1963) different levels of explanation. In doing so, I also discuss how each of the target articles in this special issue fit within these levels, and clarify why novel information associated with each level can, at times, provide unique insights into a given trait or behavior that yields significantly deeper understanding. I then overview 3 recent theoretical papers that integrate principles and findings across evolution and relationship science: love as a commitment device (Fletcher, Simpson, Campbell, & Overall, 2015), functional interdependence theory (Balliet, Tybur, & Van Lange, 2016), and the conflict-confluence model (Durante, Eastwick, Finkel, Gangestad, & Simpson, 2016). Each of these new theories/models generates many novel, specific predictions that provide excellent roadmaps for future investigators. Viewed as a whole, the target articles and commentaries that comprise this special issue reveal many of the theoretical and empirical gains that have been made in recent years.