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Posted 2021-01-11 liqu

One of the most important traits of human sociality
is homophily [1], the tendency of similar people to be
connected to each other due to their shared biological
and cultural attributes such as gender, occupation, or
political affiliation. It has been observed across various
social networks [2{8] and it is a major force behind several
pressing social issues including inequality, segregation,
and online echo chambers [9{11]. Thus a thorough
quantitative understanding of the network mechanisms
leading to homophily [12{15] is essential for promoting a
sufficient
ow of information [16] and equal opportunity
in social networks of individuals with diverse personal
preferences.
The homophily observed in social networks is often
attributed either to choice homophily, defined by people‘s
preference when choosing whom to connect with,
or to induced homophily, rising from the constraints in
the opportunities of individuals to make connections [17].
However, as suggested by longitudinal empirical results
[18, 19], these two mechanisms of homophily generation
cannot be separated without considering the cumulative
advantage-like dynamics [13] driving the evolution of soscial
networks: Choice homophily creates circumstances
for induced homophily, such as groups of similar people,
which are then further reinforced in cycles of choice and
induced homophily. While the dynamics of homophily
is well understood in the case of tipping point models of
residential segregation [20, 21], a similar understanding
of the dynamics in social networks is still needed in order
to validate and measure homophily amplification.
Here we introduce a minimal model of social network
evolution to analyse to what extent the structural constraints
caused by triadic closure affect observed homophily.
The triadic closure mechanism has been reported
as the most common structural constraint [18]
and can explain many salient features of empirical social
networks. These include a high number of closed triangles
between acquaintances and fat-tailed degree distributions
[22{25]. Thus triadic closure should be considered
as the main mechanism in most minimal dynamic social
network models [22, 26, 27]. In our approach, individuals
are considered to belong to either of the two groups
representing the values of a static attribute of interest
(gender, class, party, etc.) and they are let to rewire their
connections by two mechanisms: triadic closure (modelling
the creation of edges via current contacts) and
random rewiring [emulating any unknown mechanisms
beyond triadic closure, such as focal closure in large foci
[18, 28]]. Choice homophily/heterophily is implemented
by accepting new links with a bias probability dependent
on the similarity of attributes between individuals
(see Fig. 1 and Materials and Methods [MM] for a more
detailed model definition and parameters).s