Background: Evolution preserves social attention due to its key role in supporting survival. Humans are attracted to social cues from infancy, but the neurobiological mechanisms for the development of social attention are unknown. An evolutionary-based, vertical-hierarchical theoretical model of self-regulation suggests that neonatal brainstem inputs are key for the development of well-regulated social attention. Methods: Neonates born preterm (N = 44, GA 34 w.) were recruited and diagnosed at birth as a function of their auditory brainstem evoked responses (ABR). Participants enrolled in a prospective 8-year-long, double-blind, follow-up study comparing participants with brainstem dysfunctions and well-matched controls. Groups had comparable fetal, neonatal, and familial characteristics. Methods incorporated EEG power analysis and gaze tracking during the Attention Network Test (ANT, four cue types, and two targets) and a Triadic Gaze Engagement task (TGE, three social cue levels). Results: Results showed that neonatal brainstem compromise is related to long-term changes in Alpha-and Theta-band power asymmetries (p < .034, p < .016, respectively), suggesting suppressed bottom-up input needed to alert social attention. Gaze tracking indicated dysregulated arousal-modulated attention (p < .004) and difficulty in gaze engagement to socially neutral compared to nonsocial cues (p < .012). Conclusions: Integrating models of Autism and cross-species data with current long-term follow-up of infants with discrete neonatal brainstem dysfunction suggests neonatal brainstem input as a gateway for bottom-up regulation of social attention.