The solemnly vaginal title of Doris Lessing’s new novel, “The Cleft” (HarperCollins, 260 pages, $25.95) refers to a rock formation worshiped by a race of beach-dwelling, seal-like cavewomen (yes, the caves are on the beach), who have the capacity to conceive and become pregnant without insemination. “The Cleft [is] where the red flowers grow, and we cut them, so there is a lot of red, and we let the water flow from the spring up there, and the water flushes the flowers down through The Cleft, from top to bottom.” You get the idea, I think.

What befell this listless and uncreative colony of women (they call themselves “the Clefts”) after one of their members gave birth to a child with an unfamiliar tripartite appendage between its legs constitutes the majority of the novel’s plot. Our nameless narrator, an elderly Roman senator under the rule of Nero, has pieced the story of the Clefts together from contradictory oral histories and now presents it accompanied by thoughtful commentary and fond observations of his own slaves’ sexual horseplay. This Roman senator is didactic, tiresome, afforded way too space for an unnecessary framing device, and not going to be mentioned again in this review.

Anyway, the Clefts, having never seen a penis before, assumed their first male baby was deformed and put him out “for the eagles.” The next few they tried to castrate. Eventually some survived, escaped, and grew up in a valley a few hundred feet away (the Clefts were so torpid they’d never been that far from their caves). Due to the properties of their deformity, they came to be known as the “Squirts.” After “some kind of developmental yeast” started brewing in the younger Clefts, spontaneous conception ceased and the practice of biological sexual reproduction was cautiously adopted.

Gender roles were built into human beings at the beginning of time, as Ms. Lessing describes it: Virtually the first things the Clefts did when they arrived at the valley of the Squirts were be gang-raped and tidy up the huts. “They tore branches from the trees and used them as brooms.”While the Squirts were adventurous and liked discovery and exploration, the Clefts were “incurious” and thought “a Fish brought them from the Moon.” It’s a little disappointing that the novel deals so unimaginatively with gender: The vigorous males hunt and roughhouse, the languid females sun themselves and nag. There are no exceptions, and the reader loses interest.

Not only does the narrative offer little surprise or insight, the writing rarely engages. There are occasional passages whose content rings true and elegant (“each individual has been born to a female … and this is such a heavy and persuasive history that I am amazed we don’t remember it more often”) but for the most part, language is used clumsily throughout the novel.

Ms. Lessing has been a writer of sentences that are functional, muscular, rather than beautiful or transporting. Certainly the frankness of her voice gave “The Fifth Child” (1988) an indispensable sense of normalcy before the dread set in. (If you haven’t read that one, do.) But “The Cleft” is full of gummy, stumbling sentences in which each clause seems to trip over the next. Even when the awkwardness is deliberate (“Yes, I know, you keep saying, but what you don’t understand is that what I say now can’t be true because I am telling you how I see it all now, but it was all different then.”), it is no less aggravating.

Also there are eccentricities of syntax, among them arbitrary sentence fragments, childish run-ons, and a tedious misuse of commas. Indeed, sometimes one gets the impression that a fistful of commas was loaded into a shotgun and fired at the page: “So, then, if he was going off, with every adult male, then there would be no more babes, no more people, yes, she was right.” When an author adopts syntactic affectations that enrich a novel — that illustrate some characteristic of the speaker, that amplify or reflect thematic ideas, even that just lubricate the momentum of the narrative — then all is well in the world. But passages like the ones I’ve just quoted don’t enrich the novel; they bore the reader.

Although “The Cleft” is not a particularly interesting book, Ms. Lessing’s novels have established her over the last half-century as an intimidatingly intelligent and diverse writer. Even if most of “The Cleft” seems rushed or illconsidered, a less ambitious writer would probably not even have pursued its premise. How ironic that Ms. Lessing’s lifetime of intellectual voracity undermines her own contemptuous portrayal of her gender.

Mr. Antosca, a writer living in New York, last wrote for these pages on Antonio Muñoz Molina. His first novel, “Fires,” was published in 2006 by Impetus Press.