They found that the number of close friends (that inner 5-layer) remained remarkably stable at six individuals, but the number of best friends (essentially the sympathy group 15-layer) declined with age, and this was true of both ethnic groups. This again suggests that, as we age, we tend to sacrifice less close friends in order to invest what time

One is that each of us seems to have a natural social fingerprint in the way we allocate our social effort.

Again, there are slight differences between the sexes in the layers (women consistently tend to have more ‘5-layer’ friends than men), and both inner layers tend to increase initially with age and then decline.