Toward the very end of his book about mythology and men, Robert Bly finally turns to math. The genetic difference between men and women, he notes, amounts to just over 3 percent.

Nevertheless, he says, "I think that for this century and this moment it is important to emphasize the 3 percent difference that makes a person masculine, while not losing sight of the 97 percent that men and women have in common."His mathematical observation is something of an apologia to a book that is unabashedly about differences.

Recently, Bly has become something of a phenomenon. In this best-selling reverie about masculinity, the white-haired Bly has become a father figure for a psychic men's movement.

This is not the men's movement of the 1970s, which often seemed scripted by the women in men's lives. It is about what is lacking in men's lives today, which Bly sums up in one phrase: "There is not enough father."

Bly goes after maleness, using Grimm's fairy tale of Iron John as a text. A storyteller around the campfire, he leads men down through myth and culture to an ancient-modern idea of manhood.

The story of Iron John is far more abstract than my brief description allows. But Bly's post-chauvinist search for maleness has a counterpart to the post-feminist search for femaleness. It's as if Iron Man and Earth Mother had become separate archetypes for our time.

For most of history, woman was "other" and "other" was lesser. It is no wonder that, in the women's movement, equality was defined roughly as "sameness."

In the late 1960s, men and women were no longer opposites that attract. Men and women became, rather, persons. Mothers and fathers became parents. In the 1970s, differences were drowned by androgyny.

But in the past several years, they have re-emerged. The 3 percent has come to occupy a larger place in our minds. We talk easily about women's values, women's ways of managing and of seeing the world as if they were obviously distinct from men's.

It is again fair game to explore the psychic gender gap. Questions have recycled about whether we want maternity leave or parenting leave. After decades of integrating male schools, there is again a feminist argument in favor of educating adolescent girls separately.

Bly himself believes that only men can make men. He tells a story, approvingly, about a tribe in which boys live with their mothers until the men come and - with the complicity of the women - kidnap the children and turn them into men. He says there is not enough "father," as distinct from "parent."

For my own part, I would like to believe that the current fascination with differences is indeed "post-feminist," "post-chauvinist." That we are now so comfortable with equality that we are no longer threatened by differences. That the age of androgyny has simply passed like massive shoulder pads on the old power suits. Something softer will do.

But Bly's differences seem less like harbingers of a new men's movement than of the old. Bly's descriptions of women, and of relationships, are often more reminiscent of the '50s than the '90s. His search for the male reminds me a touch too much of the days when the tom-toms sounded and the women were kept from the ceremonies.

Is it important, as he says, to emphasize the 3 percent? Differences may make it easier to understand ourselves, or harder to understand each other. But sometimes this new interest in gender resonates with the slight snap of a backlash.