Like any social phenomenon, the systemic outbreak of loneliness has more roots than one. But surely its fundamental source, for young and old alike, is the arithmetical one: the fact that more and more people now pass through life without father, sister, brother, children, cousins or varying combinations of the above — and sometimes without any of the above.

Or consider another signal development of the age that also contributes to social disunity: identity politics. In this case, too, dots connect to post-1960s kinship implosion. “The Combahee River Collective Statement,” agreed by all to be the founding document of such politics, is a manifesto acclaiming group identity as the most important source of power and protection.

It was issued in 1977, just as the first generation born after the sexual revolution came of age. It was the creation of a group of black feminists, representing a demographic cohort that was the first to experience rising and disproportionate rates of abortion and fatherlessness.

“The only people who care enough about us to work consistently for our liberation are us,” these feminists said plaintively. That statement captured a sad reality that would soon become true for many more Americans: not even having family to count on.