The word is relatively new, but the idea has been around for decades.
Not all that long ago, an American statesman of considerable influence wrote an opinion piece for this very publication, about a political issue that directly affects women. It was perhaps the finest example of mansplaining ever published.
This election season, the idea of "mansplaining"—explaining without regard to the fact that the explainee knows more than the explainer, often done by a man to a woman—has exploded into mainstream political commentary. Hugo Schwyzer over at Jezebel noted its growth in September, writing that it has "moved beyond the feminist blogosphere." And, sure enough, these days pretty much every time a male politician opens his mouth about so-called women's issues he is dubbed, like so or like so, a mansplainer.
But the article in question wasn't written this year. Its author was Lyman Abbott, a prominent New England theologian, and it appeared in the Sept. 1903 issue of The Atlantic. The article was called "Why Women Do Not Wish the Suffrage." Abbott writes:
I believe it is because woman feels, if she does not clearly see, that the question of woman suffrage is more than merely political; that it concerns the nature and structure of society,—the home, the church, the industrial organism, the state, the social fabric. And to a change which involves a revolution in all of these she interposes an inflexible though generally a silent opposition. It is for these silent women—whose voices are not heard in conventions, who write no leaders, deliver no lectures, and visit no legislative assemblies—that I speak.
See, even though the women in question haven't said anything about it, Lyman Abbott totally knows what they want better than they do. Any woman in favor of suffrage just doesn't get the true female experience as well as he does.
Turns out 2012 isn't really the year of the mansplainer. The only reason we think it so is that the word itself didn't exist until recently.
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The commonly cited birthday of the idea is 2008. That year, a portion of an essay by Rebecca Solnit, called "Men Explain Things To Me," appeared in the Los Angeles Times. Solnit didn't use the word "mansplain"; she merely, well, explained it, describing the time a man explained a book to her without acknowledging that she herself wrote it. (This August, she wrote that the men-explaining-things essay has been one of the most reposted pieces she's ever done.) According to Know Your Meme, the word first showed up online about a month after the LA Times piece, in the comments section on a LiveJournal community. Awareness increased slowly but steadily, mostly on feminist blogs, until it was suddenly all over the place: a Google trends graph of searches for the word is mostly a straight line until this past summer, when in August it appeared in a GQ political blog titled "The Mittsplainer" as well as an xoJane.com post critical of the word. There's another even larger jump in October, perhaps linked to the birth of Mansplaining Paul Ryan.
The idea wasn't political in origin, and mansplaining happens in academia and offices and dining rooms. But it makes sense that politics brought it to the general public's attention. When it comes to politics, it seems men have been talking about the female experience since basically forever.