Separated twins reunited in Small World
There was a story in the news in Poland, few months ago, about a peculiar baby-swap and reunion. Identical twins were born and soon one of them was incidentally swapped with other baby girl during the bathing at the hospital. Two mothers returned home (one no longer considering her twins identical, the other not even suspecting that anything wrong had happened to her child) and so the twins have been separated for seventeen years. The press accounts of their reunion suggested that their eventual meeting, the fact that the girls had some mutual friends or acquaintances who made the reunion possible, was to some extent accidental. However, the network structure and dynamics of social world, and the fact that twins are actually so similar, should make such reunions rule rather than exception.
Two related mechanisms are important here. One is homophily, the tendency of human beings to associate with others who are similar to them . The other mechanism is “triadic closure” which describes the inclination of people to befriend the friends of their friends. The consequence of those mechanisms for a particular person is the contraction of social space (space made of people connected by social bonds) around this person, as he or she creates relational shortcuts by getting to know friends of his/her friends. Because of homophily, which makes us bond with people similar to ourselves, this social space contraction creates a rather homogeneous cluster, that is, locally dense network of similar people.
Now consider two nodes (girls) embedded in such a network space of social relations, the nodes that are very alike (in terms of their preferences, choices they make), just the way identical twins are. Because of a past misfortune, a baby swap, they are separated, don’t know each other. However, the theory of small worlds teaches us that they cannot be very far away in social terms. You would be able to cross the social space between them, from person to person, in a really small (say around six) number of steps. One of the things the girls are busy with during their life is getting to know new people, making friends and creating social relations, Around the age of seventeen this activity gets really intense. One of the ways for them to meet new people is through the mediation of those they already know (triadic closure). This way the girls create shortcuts to the people they didn’t know before directly, and by doing this they shrink and cluster the social networks around them. The point is that each new friend is in some way like them because of the homophily mechanism. And because those two girls are so similar (and this is apparently one of the stories of mystical, total twin similarity in tastes, behaviors etc.) each new friend draws them closer. They gravitate towards each other inevitably, the distance between them can be measured in less and less people, until they both get to know the same person, and that person soon notices physical similarity between sisters (or even takes one for the other) and arranges the meeting.
There are issues that complicate the above simple and clear picture. When considering homophily it is realistic to assume that people perceive similarity to others using a number of dimensions, not the totality of features at once. Geography matters too; both girls live in Warsaw, and that must have added to the probability of their meeting. Still it is an example of how our understanding of events of social reality can shift from notions such as “accidental” towards descriptions that involve more of a sense of complex mechanics.
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