Why don't black women marry?

That too many African-American children are growing up in single-parent households isn't news.

But Stanford law Prof. Ralph Richard Banks has initiated a provocative debate that analyzes why black women are the most unpartnered group in our society.

In his new book, "Is Marriage for White People?" Banks explains: "The percentage of black children born to unwed parents exceeds 70 percent not because single women are getting pregnant more often, but because black women are so much more likely to be single. Unwed childbearing is yet another consequence of the marriage decline."

In other words, the prevalence of unwed black mothers is not attributable to differing sexual mores between whites and blacks, but rather to the fact that black women are living what Banks describes as a segregated existence.

Asians, Latinos and even black men are much more likely to marry outside their race. But black women, according to Banks, face social pressure to marry within their race -- they are encouraged to marry "down" before they marry "out."

And those social pressures do not apply to black men.

"Pressures to marry within a group are receding for all groups, including black men," Banks told me. "But for black women, they are seen as having a special responsibility to black men and to restore the black family, but those efforts are counterproductive and have been unsuccessful.

Typically, Banks notes, the more educated a woman, the more likely she will marry. But that's not so with African-American women.

They're dealing with a shortage of potential male partners, which Banks surmises is caused by a high incarceration rate, interracial marriage (which, he writes, "depletes the pool of men for middle-class, college-educated black women") and economic trends that have benefited women more than men (and that are much more pronounced among African-Americans).

By his logic, the first family is unique in a way I didn't appreciate before reading the book.

Regarding President and Michelle Obama, Banks writes: "As African-Americans, they are extraordinary in the most ordinary way: They are a married couple raising their children together."

Banks' work is the sort of dissertation on a touchy subject best coming from someone within the community.

Which gets to the most controversial aspect of his assessment:

"At the core of the problem is that nearly twice as many black women as black men graduate from college. So what are educated black women going to do when there are only half as many black men in their college classrooms or professional environment?" he wondered during a recent conversation with me.

Banks told me that if he had a daughter, he'd advise her to look outside her race. "It is amazing it hasn't happened more," he said. "Black women have the thinnest pool of partners within their race."

The blogosphere is alive with criticism of his counsel that black women be more open to partners of different backgrounds.

"One of the points of the book is to undo that problem and give black women the freedom to make decisions that are right for them. That will often entail crossing the race lines," he said.

"Part of the reason I wanted to write the book was to change the conversation -- to enrich and deepen it," he told me. "It is a sad commentary that if it were written by a [white person] it would not be so well-received.

"The same forces that undermine marriage for African-Americans are actually in operation throughout American society and are reshaping or undermining marriage for everyone," Banks said.