Abstract
The number of social relationships that a single human being can possibly be involved in is limited because individuals face time constraints (that is, time costs) in constructing and maintaining social relationships; furthermore, the distribution of the strength of such relationships (as measured by frequency of social interaction) looks significantly skewed (a power law distribution), that is, a few strong relationships and many weak relationships. This skewedness suggests that the costs and benefits of bonding with others depend on the strength of the social relationships: if it involves uniform costs and benefits, the distribution would not be skewed. The bonding is known as social grooming; that is, humans strategically construct their social relationships, and thus, complex human societies should also be strategically constructed. Therefore, it is important to know their strategies for understanding human societies. Previous studies provide evidence of social grooming strategies by examining the evolution and the difference between the various social grooming methods. However, quantitative laws that are important for theoretically understanding human societies are still open to investigation. Social big data is a particularly powerful tool for finding such laws. Therefore, we analyse data from six communication systems (Twitter, a social networking site providing two types of interactions, an avatar chat, a mobile phone and a short message service). We find a simple quantitative law by which social relationships are constrained Nma (a>1); here, N is the number of social relationships and m is a mean of the strength of those relationships. The fact that deep social relationships require higher costs per relationship than shallow relationships is suggested by a>1 (if the both is equal then a will be 1), because the effect of m on the constraint increases with m. For exploring why a is greater than 1, we conduct an individual-based simulation where social grooming costs are assumed to increase linearly with the strength of social relationships. Our results indicate that this model fits all data sets; that is, it displays an explanation capacity for the phenomenon. In addition, an analysis of this simulation proves our assumption about the social grooming cost increasing with the strength of social relationships as being true. Moreover, it suggests that its gradient increases the width and shallowness of these relationships. The law and its causes suggest that mankind’s evolution of social grooming has enabled changing social structures, and the phenomenon is because of the constraints of the social network generation. These findings will contribute towards an explanation of the evolution of the various social grooming methods of humans and their significantly large social group.
Highlights
On the other hand, having many weak social relationships helps in obtaining a variety of information which is advantageous in a complex society (Granovetter, 1973; Dunbar, 2004; Eagle et al, 2010; Arnaboldi et al, 2013c)
This study aims to discover how social grooming methods influence time cost distribution strategies of the methods and social structures depending on those strategies
The results of the analysis show that communication volumes v increased along with the relationship strength d and the gradients were independent of the number of days of the data periods t
Summary
On the basis of the social brain hypothesis (Byrne and Whiten, 1989; Whiten and Byrne, 1997; Dunbar, 2000; Dunbar, 2003), an explanation of social structures, which are typical for humankind, is expected to offer knowledge about human origins, such as the limitation on the number of social relationships (Dunbar, 2000; Dunbar, 2003; Hill and Dunbar, 2003; Gonçalves et al, 2011; Arnaboldi et al, 2013a) and the skewness of social relationships (Zhou et al, 2005; Hossmann et al, 2011; Arnaboldi et al, 2012; Hu et al, 2012; Song et al, 2012; Arnaboldi et al, 2013b; Fujihara and Miwa, 2014), that is, its distributions following a power law (Hossmann et al, 2011; Arnaboldi et al, 2012; Hu et al, 2012; Pachur et al, 2012; Song et al, 2012; Fujihara and Miwa, 2014). Social grooming is used to construct and maintain social relationships This behaviour is important in complex human societies (Dunbar, 2000). On the other hand, having many weak social relationships helps in obtaining a variety of information which is advantageous in a complex society (Granovetter, 1973; Dunbar, 2004; Eagle et al, 2010; Arnaboldi et al, 2013c)
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