You filled out a questionnaire, fed it into the machine, and almost instantly received a card with the name and address of a like-minded participant in some far-flung locale—your ideal match. He called up his friend Robert Ross, a programmer at I. M., and they began considering ways to adapt this approach to find matches closer to home. “This loser happens to be a talented fashion illustrator for one of New York’s largest advertising agencies.

The Pill, women in the workforce, widespread deferment of marriage, rising divorce rates, gay rights—these set off a prolonged but erratic improvisation on a replacement.

In a fractured and bewildered landscape of fern bars, ladies’ nights, Plato’s Retreat, “The Bachelor,” sexting, and the concept of the “cougar,” the Internet promised reconnection, profusion, and processing power.

They approach the primeval mystery of human attraction with a systematic and almost Promethean hand.

They rely on algorithms, those often proprietary mathematical equations and processes which make it possible to perform computational feats beyond the reach of the naked brain.

Men were asked to rank drawings of women’s hair styles: a back-combed updo, a Patty Duke bob.

Another question, in a section called “Philosophy of Life Values,” read, “Had I the ability I would most like to do the work of (choose two): (1) Schweitzer. (3) Picasso.” Some of the questions were gender-specific.

One section asked subjects to choose from a list of “dislikes”: “1. The batteries died on her tape recorder, so they made a date to finish the interview later that week, which turned into dinner for two.

The demolition of the Third Avenue Elevated subway line set off a building boom and a white-collar influx, most notably of young educated women who suddenly found themselves free of family, opprobrium, and, thanks to birth control, the problem of sexual consequence.

Others choose for you; they bring five boxes of cereal to your door, ask you to select one, and then return to the warehouse with the four others. It is tempting to think of online dating as a sophisticated way to address the ancient and fundamental problem of sorting humans into pairs, except that the problem isn’t very old.

Civilization, in its various guises, had it pretty much worked out.

Lives hang in the balance, and yet we have typically relied for our choices on happenstance—offhand referrals, late nights at the office, or the dream of meeting cute.