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Kagan theorized biologically based temperament types that are present in infancy, stable across development, and essential for understanding individual differences. Despite evidence, temperament research remains focused on a few prominent dimensions of temperament, without adequately addressing covariance among dimensions and temperament types. Using longitudinal twin data, we took a person-centered statistical approach to identify temperament types and examined continuity and change across five developmental periods (Ninfancy = 602; Ntoddlerhood = 522; Nearly childhood = 390; Nlate childhood = 718; Nearly adolescence = 700). We then examined the genetic and environmental etiology of temperament types. Twins were boys and girls (51–53% female), primarily Hispanic/Latinx (23–30%) and non-Hispanic/Latinx White (56–63%), and from socioeconomically diverse families (28–38% near-or-below the poverty line). Using latent profile analysis, we identified three temperament types at each age characterized by negative reactivity and dysregulation, positive reactivity and strong self-regulation, and moderate reactivity and regulation. Latent transition analyses revealed considerable continuity in membership type for "negative dysregulated" beginning in infancy, log odds = 1.58 (SE =.65) to 3.16 (SE =.77), p <.01, of remaining relative to transitioning to "typical expressive", and "positive well-regulated" beginning in early childhood, log odds = 1.41 (SE =.56) to 2.25 (SE =.47), p <.05. Twin analyses revealed moderate heritability and a consistent role of the shared environment on positive well-regulated, with negative dysregulated and typical expressive also moderately heritable with the shared environment being important at some ages. Findings support the presence of theorized biologically based temperament types that develop rapidly in infancy and toddlerhood and provide a foundation for the study of individual differences and risk and resilience processes across the lifespan. Public Significance Statement: Children can be classified into three types based on their temperament: negative dysregulated, positive well-regulated, or typical expressive. These types develop rapidly across infancy and toddlerhood becoming more continuous by early childhood. Types are both heritable and influenced by the early environment, supporting a complex interplay between temperament and sociocultural context when predicting children and adolescent's adaptation. [ABSTRACT FROM AUTHOR]

Premature infants may be at risk for lower effortful control, and subsequent lower academic achievement, peer competence, and emotional and physical wellness throughout the lifespan. However, because prematurity is related to obstetrical and neonatal complications, it is unclear what may drive the effect. Effortful control also has a strong heritable component; therefore, environmental factors during pregnancy and the neonatal period may interact with genetic factors to predict effortful control development. In this study, we aimed to dissect the influences of genetics, prematurity, and neonatal and obstetrical complications on the development of effortful control from 12 months to 10 years using a twin cohort. This study used data from the Arizona Twin Project, an ongoing longitudinal study of approximately 350 pairs of twins. Twins were primarily Hispanic/Latinx (23.8%–27.1%) and non-Hispanic/Latinx White (53.2%–57.8%), and families ranged in socioeconomic status with around one third falling below or near the poverty line. Of the twins, 62.6% were born prematurely. Effortful control was assessed via parent report at six waves. There was not a significant relationship between gestational age and effortful control regardless of whether obstetrical and neonatal complications were controlled for. Biometric twin modeling revealed that the attentional focusing subdomain of effortful control was highly heritable. Gestational age did not moderate genetic and environmental estimates. Our findings help inform the risk assessment of prematurity and provide evidence for the differing etiology of each subdomain of effortful control and the strong role of genetics in effortful control development. Public Significance Statement: This study advances the current understanding of the development of effortful control. There was no compelling evidence that premature birth was a risk factor for lower effortful control. Further, although effortful control is heritable, particularly the attentional focusing subdomain of effortful control, the genetic and environmental estimates for effortful control were not influenced by obstetrical and neonatal complications. [ABSTRACT FROM AUTHOR]