Emotional closeness to friends declined steadily once regular contact stopped. Emotional closeness to kin held up across the same long gaps. Time since last contact tracks closely with how close a friendship feels.
How it was done
An 18-month longitudinal study tracking emotional closeness and contact frequency across people’s personal networks, separating kin from friends.
What it means
The asymmetry is the point. Kin relationships are cheap to maintain — they survive a year of silence and resume more or less where they left off. Friendships are not. They carry an ongoing maintenance cost, and the bill comes due whether or not anyone intended to stop paying it.
A companion paper from the same authors found communication frequency strongly associated with the emotional intensity of a relationship, which is the same result seen from the other side.
This is why "we’ll pick up where we left off" is true of a sibling and unreliable of a friend. The friendship was never held up by the shared history alone.
