  We compare face-to-face interaction data recorded by wearable sensors in
various sociological environments. The interactions among individuals display a
clear environment-dependent diversity in agreement with previous analyses. The
contact durations follow heavy-tailed distributions although not exactly of
power-law type as previously suggested. Guided by the common patterns observed
for each relation, we introduce a variable named the duration contrast, which
reveals a common behavior among all datasets. This suggests that our tendency
to spend more or less time than usual with a given individual in a face-to-face
relation is not governed by social rules but by a common human trait.
Additional data shows that it is the same for baboons. Furthermore, we propose
a new kind of model to describe the contacts in a given relation based on the
recently introduced concept of Levy Geometric Graphs. It reproduces the data at
an impressive level. The associated Levy index is found to be alpha = 1.1 on
all the datasets, suggesting a universal law for primates and opening many
exciting perspectives.
