The number of relationships peaks around twenty-five
Mobile phone data made it possible to trace a curve that self-report surveys suggested without demonstrating. Its shape is more regular than expected.
What contact data show
An analysis published in 2016 by Kunal Bhattacharya, Asim Ghosh, Daniel Monsivais, Robin Dunbar and Kimmo Kaski uses call records for several million subscribers, allowing the number of distinct contacts to be tracked by age.
The curve rises to a maximum in the early twenties, then falls steadily over several decades, a shape found for both sexes with a few years' offset.
These data have an advantage surveys lack: they record what happens, without going through memory or through the image each person wishes to present. They have the mirror-image drawback of knowing nothing about the meaning people give to these exchanges.
What those data do not say
A call is not a relationship. The number of distinct telephone contacts measures an activity, and it is sensitive to how the medium is used, which varies sharply by age and period. A call to the plumber counts as much as a call to a friend of thirty years.
The rise of messaging apps has moved part of the traffic off the classic telephone network, which makes long series hard to compare and might exaggerate the measured decline at older ages.
Agreement with surveys
Self-report surveys find the same general shape: a maximum in early adulthood, then a decline. The meta-analysis by Cornelia Wrzus and colleagues, published in 2013, arrives at this shape for the global network. Levels differ by instrument, but the shape is stable.
That convergence between two sources with independent biases is the strongest argument for the result, more than either source taken alone. The same meta-analysis notes, however, that some circles, such as the family, remain stable for much longer.
Proposed explanations
Two families of explanation coexist. The first is structural: contexts for meeting become scarce, and work and family commitments reduce available time.
The second is motivational: socioemotional selectivity theory, formulated by Laura Carstensen, proposes that perceiving a shorter time horizon leads people to concentrate exchanges on the most meaningful relationships. On this reading, the fall in number signals not impoverishment but reorganisation.
How to separate them
Work experimentally manipulating the perception of time horizon finds effects compatible with the second hypothesis, on measures of reported preference. Young adults asked to imagine an imminent departure more often choose, like older people, the company of someone close rather than that of a stranger.
The two mechanisms are not exclusive and produce the same curve. Distinguishing them requires observing people whose constraints change without their age changing, which few designs allow.
Key points
Call records place the maximum of distinct contacts in the early twenties.
A telephone contact is not a relationship, and use of the medium varies with age.
Structural and motivational explanations produce the same curve.
This article describes documented mechanisms and disagreements. It recommends no position, no party and no vote, and commits to no reading other than that of the work it cites.
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