Limitations of Time Resources in Human Relationships Determine Social   Structures
  A single human can be involved in a limited number of social relationships, and the distribution of strengths of such relationships shows significant skew. This skewness suggests that the costs and benefits of the social interactions required to bond with others (social grooming) depend on the social relationship strength: if they involved uniform costs and benefits, the distribution would not be skew. Here, we show that the cost of social grooming increases with the social relationship strength, and its gradient determines the structures of these relationships in society as evident from an analysis of data from six communication systems. This may be due to an increase in communication volumes, such as number of characters and duration of calls, along with an increase in the social relationship strength. We tested this hypothesis using an individual-based simulation where social grooming costs were assumed to increase linearly with the social relationship strength; this is the simplest assumption. The results indicated that this model fitted all data sets, i.e., it showed an explanation capacity for the phenomenon. Additionally, an analysis of this simulation suggested that the gradient of social grooming costs increases the width and shallowness of social relationships in its communication system. 
Masanori Takano and Ichiro Fukuda
cs.SI physics.soc-ph