This research model moves from a comprehensive review of SIDS research to a consideration of the evolution of human infant development and why we should expect to find that especially in the first year of life, parent-infant sleep contact asserts a significant physiological regulatory effect on the infant's breathing. Prenatal studies of fetal hearing and breathing are reviewed and used to argue that the central nervous system is at birth already sensitized to parental breathing rhythms to which the infant in its "expected" postnatal environment will have access. This perspective shows that important continuities exist between fetal experiences and infant respiratory behavior. Emerging from an integration of clinical, experimental, and developmental studies with an evolutional perspective (which includes cross-species and cross-cultural data) it is hypothesized that access to parental sensory breathing cues (movement, sound, touch, and expelled CO2) ought to help one of many subclasses of infants to override breathing control errors, some of which may be involved in SIDS.This model and the testable hypotheses which emerge from it do not suggest that parent-infant cosleeping necessarily should be recommended, or that it is always safe for the infant; only a careful analysis of the entire constellation of family attributes can determine this. Rather, the paper argues that for some infants certain CNS deficits suspected to be involved in SIDS may interact with nocturnal separation from parental breathing cues (a novel experience for our species) to increase crib death risk and, thus, must be considered as one of the many aspects in the unfolding pathophysiology of SIDS for some victims. This model is offered not as a substitute for the traditional SIDS research model which assumes the primacy of internal breathing control mechanisms, but as a complementary research approach-one in which both internal and external (environmental) factors are thought to interact to affect breathing behavior. This interactional model is justified by a variety of data revealing that aspects of parent-infant physiological synchrony are best understood in terms of the four million years in which parent-infant contact was almost certainly continuous for the infant during the first year of life wherein a high degree of postnatal immaturity is characteristic.