During an experiment on infant behavior, it was observed that young children shared toys with their mothers; therefore, a series of research studies was designed to investigate this phenomenon. The general purposes of the research were: (1) to define sharing more precisely and develop objective measures of frequency and duration for it, (2) to analyze the order in which sharing behaviors occur, (3) to investigate characteristics of objects that children would share and the persons who would be shared with. Data were taken from laboratory studies and field observations. Study subjects were 18 months old. Sharing was defined in terms of the following three responses: showing objects, giving objects, and playing with them while in contact with another individual. The studies included analysis of several variables: (1) effects of novel versus familiar toys, and toy versus nontoy objects, (2) effects of differential social reinforcement, (3) recipients other than the mother (fathers, relatively unfamiliar persons), and (4) effects of environmental changes (decorations) on the showing component of sharing. Discussion focuses on the learning processes that may be involved in the origins of sharing, which is viewed as an adaptive response. Sharing in other species and in prehistoric man are also considered. (DP)