  The social network maintained by a focal individual, or ego, is intrinsically
dynamic and typically exhibits some turnover in membership over time as
personal circumstances change. However, the consequences of such changes on the
distribution of an ego's network ties are not well understood. Here we use a
unique 18-month data set that combines mobile phone calls and survey data to
track changes in the ego networks and communication patterns of students making
the transition from school to university or work. Our analysis reveals that
individuals display a distinctive and robust social signature, captured by how
interactions are distributed across different alters. Notably, for a given ego,
these social signatures tend to persist over time, despite considerable
turnover in the identity of alters in the ego network. Thus as new network
members are added, some old network members are either replaced or receive
fewer calls, preserving the overall distribution of calls across network
members. This is likely to reflect the consequences of finite resources such as
the time available for communication, the cognitive and emotional effort
required to sustain close relationships, and the ability to make emotional
investments.
