  Core-periphery is a key feature of large-scale networks underlying a wide
range of social, biological, and transportation phenomena. Despite its
prevalence in empirical data, it is unclear whether this property is a
consequence of more fundamental network evolution processes. While preferential
attachment can create degree heterogeneity indistinguishable from
core-periphery, it doesn't explain why specific groups of nodes gain dominance
and become cores. We show that even small amounts of assortative attachment,
e.g. homophily in social networks, can break this symmetry, and that the
interplay of the two mechanisms leads to one of the groups emerging as a
prominent core. A systematic analysis of the phase space of the proposed model
reveals the levels of assortative and preferential attachment necessary for a
group to become either core or periphery, depending on initial conditions. We
find that relative group size is significant, with minority groups typically
having a disadvantage on becoming the core for similar assortative attachment
levels among groups. We also find that growing networks are less prone to
develop core-periphery than dynamically evolving networks, and that these two
network evolution mechanisms lead to different types of core-periphery
structures. Analyzing five empirical networks, our findings suggest that core
nodes are highly assortative, illustrating the potential of our model as a tool
for designing and analyzing interventions on evolving networks.
