A major distinction is discovered among severely retarded adults which appears to parallel the distinction between man and animal. The more capable severely retarded engage in many forms of uniquely human behavior. In contrast, the less capable severely retarded initiate none of this behavior. No individuals were found to be intermediate between the two levels of ability, suggesting that the distinction involves a threshold.

This book provides the evidence for and against the distinction and systematically examines the differences and similarities between the two levels. Over 70 types of activity and interaction are carefully defined and examined in detail. This behavior includes speech, gestures, facial expressions, affection, aggression, control of others, care of others, cooperation, humor, play, imagination, use of objects, concern with possessions, territoriality, and personal identification. Case material is used to illustrate generalizations and conclusions.

A thorough examination is made of how the institutional ward operates in terms of the distinction between these two levels of ability. Daily routines, patterns of ward use, standards of desired behavior, and staff interaction with residents are all investigated.

Social scientists will find this a useful source of information about fundamental behavior patterns in humans. Data are organized to facilitate comparisons of both levels of severe retardation with lesser retarded, "normal" humans, and members of other species.