The papers in the present symposium stem from field research and seminar discussions that have been in progress at Cambridge for four or five years. The most promising advance in recent research on the social structures of homogeneous societies has been the endeavour to isolate and conceptualize the time factor. By this I do not mean the amorphous subject matter usually labelled 'culture change' or 'social change'. I mean the more fundamental and difficult problems involved in the truism that the idea of society, the notion of a social system or a social structure, necessarily implies extension through a stretch of time. A social system, by definition, has a life. It is a social system, that particular social system, only so long as its elements and components are maintained and adequately replaced; and the replacement process is the crucial one because the human organism has a limited life span. Maintenance and replacement are temporal phenomena. It is the processes by which they are ensured that concern us when we study the time factor in social structure.
These processes have biological determinants. One is the life span of the individual; the other is the physical replacement of every generation by the next in the succession of death and birth. We must leave to physiology, genetics and demography the exact study of these determinants. It is enough to remind ourselves that a social system will not persist if the average life span of its members is too short for them to have offspring and to rear them to the age when they in turn can have offspring, or, in demographic terms, if the balance of births and deaths does not yield a net reproduction rate of unity or more. From the anthropological point of view, the important thing is that the physical growth and development of the individual is embodied in the social system through his education in the culture of his society, and the succession of the generations through their incorporation in the social structure. The facts of physical continuity and replacement are thus converted into the process of social reproduction.
These generalities can be put in another way. For a social system to maintain itself its two vital resources must be maintained at an adequate level by continuous use and replacement. These two resources are its human capital and its social capital, and it is the latter that specially concerns the anthropologist. It consists of the total body of knowledge and skills, values and beliefs, laws and morals, embodied in the customs and institutions of a . . .