We hypothesize that maternal sensory exchanges, likely involving a combination of heat, sound, gas, smells, movement, and touch, induce important physiological changes, especially in the healthy infant's arousal patterns, body temperature, and sleep architecture as defined by standard physiological measures. We summarize the results of two preliminary physiological studies, and some early data from a third, in which mothers and infants are monitored using standard polysomnographic techniques as they sleep in the same bed, and then in adjacent rooms. Our data suggest that infant-parent co-sleeping alters the infant's sleep experience as, for example, the characteristics of arousals, the frequency and duration of nursing, infant sleep position and the number of maternal inspections. For example, while sleeping in the same bed, mothers nurse their infants three times more frequently than they do while their infants sleep in an adjacent room. These preliminary data demonstrate significant differences between routine co-sleeping and solitary sleeping environments. This work underscores the importance of studying infant sleep as it unfolds in the co-sleeping environment, the environment within which it evolved over at least 5 million years of human evolution. Should our preliminary findings be confirmed in future studies they will provide a beginning point for considering additional, possibly unconventional ways of helping to reduce SIDS risks.