This section introduces three major components of socioemotional behavior: externalizing problem behaviors, internalizing problem behaviors, and adaptive behaviors, and a Multidimensional Peer Nomination Inventory for their assessment. The inventory was developed within the framework of the model of emotional and behavioral regulation (Chapter 1). Parallel versions are available for peer nomination, teacher rating, and parental rating. Research results presented in Chapters 8 to 12 are based on JYLS data (Chapter 1) and FinnTwin12 data (Chapter 3). For the JYLS data, analyses are extended to both the school-aged offspring and the aging parents of the original sample. Thus three generations are met in this section.

Chapter 8 by Vierikko and Pulkkinen shows that independent of the informant, boys exceed girls in externalizing problem behaviors, and girls exceed boys in internalizing problem behaviors and adaptive behaviors. Both types of problem behaviors decrease from ages 12 to 14 whereas compliant behavior increases. Typically, additive genetic factors explained about half of the phenotypic variance in socioemotional behavior for boys and girls, and half of the variance was attributed to environmental factors. Significant variation from this 50–50 split in sources of variance was, however, evident across gender and across dimensions of socioemotional behavior. Gender differences emerged in aggression, depression, anxiety, and social activity.

Chapter 9 by Kokkonen and M-L. Kinnunen analyzes the construct of emotion regulation as a process and an outcome. Emotion regulation strategies may be adaptive or maladaptive. Emotion regulation deficiency in adults is related to poor physical and mental health.