In the framework of the “Fruits of Ethology” guest talk series we will have the pleasure to welcome our next speaker, Tamas David-Barrett (Universidad del Desarrollo, Santiago de Chile; University of Oxford, United Kingdo; Kiel Institute for the World Economy, Germany; Population Research Institute, Helsinki, Finland ).
Date: 15th of February, Thursday, 17.00
Location: ELTE, South Building, 7.110, Pázmány Péter sétány 1/c
Title: Falling Fertility Creates Trust Gap: Changing Social Network Structure in Demographic Transition
Traditional human societies use two of biology’s solutions to reduce free-riding: by collaborating with relatives, they rely on kin-selection mechanism, and by forming highly clustered social kin-networks, they can efficiently depend on reputation dynamics. However, both of these solutions assume the presence of relatives. This model shows how social networks change during demographic transition. With falling fertility, there are fewer children that could be relatives to each other. As the missing kin is replaced by non-kin friends, local clustering in the social network drops. This effect is compounded by increasing population size, characteristic of demographic transition. At the same time, with falling fertility the average graph distance deceases, ballooning the set of indirect social contacts two-steps away. A second model shows that the speed at which reputation spreads in the network slows down due to both falling fertility and increasing group size. Thus the demographic transition weakens both mechanisms of free-rider reduction: there are fewer relatives around, and reputation spreads slowly. This new link between falling fertility and the altered structure of the social network offers novel interpretations to the origins of legal institutions, the Small World phenomenon, the social impact of urbanisation, and the birds-of-a-feather friendship choice heuristic
Márta Gácsi & Ádám Miklósi