In his disordered, sprawling novels, Mailer takes a hopped-up, quasi-religious view of sex, with flights of D. H. Lawrence-inspired mysticism and a special interest in sodomy. In “An American Dream,” he describes a woman’s genitals: “It was no graveyard now, no warehouse, no, more like a chapel now, a modest decent place, but its walls were snug, its odor was green, there was a sweetness in the chapel.”

Mailer’s most controversial obsession is the violence in sex, the urge toward domination in its extreme. A sampling: “I wounded her, I knew it, she thrashed beneath me like a trapped little animal, making not a sound.” “He must subdue her, absorb her, rip her apart and consume her.” It is part of Mailer’s existentialism, his singular, loopy philosophy, that violence is good, natural and healthy, and it is this in his sex scenes that provokes. As in many of Mailer’s ventures, like his famous campaign for mayor of New York, it’s not entirely clear how much he means it and how much is for fun, for the virile show.

It would be too simple to call the explicit interludes of this new literature pornographic, as pornography has one purpose: to arouse. These passages are after several things at once — sadness, titillation, beauty, fear, comedy, disappointment, aspiration. The writers were interested in showing not just the triumphs of sexual conquest, but also its loneliness, its failures of connection. In his unruly defense of sexually explicit male literature in “The Prisoner of Sex,” Mailer wrote: “He has spent his literary life exploring the watershed of sex from that uncharted side which goes by the name of lust and it is an epic work for any man. . . . Lust exhibits all the attributes of junk. It dominates the mind and other habits, it appropriates loyalties, generalizes character, leaches character out, rides on the fuel of almost any emotional gas — whether hatred, affection, curiosity, even the pressures of boredom — yet it is never definable because it can alter to love or be as suddenly sealed from love.”

In the intervening decades, the feminists objected; the public consumed; the novelists themselves were much decorated. And then somewhat to their surprise, the old guard got old. In books like Roth’s “Exit Ghost” and Updike’s “Toward the End of Time,” they began to take up the subject of impotence in various forms. Was it possible that the young literary gods had fallen? Roth wrote in “Zuckerman Unbound”: “Life has its own flippant ideas about how to handle serious fellows like Zuckerman. All you have to do is wait and it teaches you all there is to know about the art of mockery.”

And so we come back to the copy of “The Humbling” in the garbage can on the subway platform. The problem with the sex scenes in Philip Roth’s late work is not that they are pornographic, but that they fail as pornography. One feels that the author’s heart is not in it, that he is just going through the motions; one feels the impatient old master mapping out scenes (dildo, threesome), not writing them. The threesome in “The Humbling” has none of the quirkiness, the energy, the specificity of the threesomes in “Portnoy’s Complaint,” either the one where “the Monkey” eats a banana and gets her name, or the one where they pick up an Italian prostitute who later brings her son, all dressed up in his Sunday best, to see them. In the stripped-down later novels (“Everyman,” “Exit Ghost,” “Indignation”), Roth seems to have dispensed with the detail and idiosyncratic richness of his earlier work. As he writes about old men failing at sex, and raging about failing at sex, we see the old writer failing at writing about sex, which is, of course, a spectacle much more heartbreaking.

At this point, one might be thinking: enter the young men, stage right. But our new batch of young or youngish male novelists are not dreaming up Portnoys or Rabbits. The current sexual style is more childlike; innocence is more fashionable than virility, the cuddle preferable to sex. Prototypical is a scene in Dave Eggers’s road trip novel, “You Shall Know Our Velocity,” where the hero leaves a disco with a woman and she undresses and climbs on top of him, and they just lie there: “Her weight was the ideal weight and I was warm and wanted her to be warm”; or the relationship in Benjamin Kunkel’s “Indecision”: “We were sleeping together brother-sister style and mostly refraining from outright sex.”