The vast majority of Americans, regardless of gender, are never going to serve on a Fortune 500 company's board of directors. Consequently the gross gender imbalance in board seats is not necessarily something that the woman on the street spends a lot of time fuming about. Nonetheless, the imbalance is striking, and I think people ought to pay more attention to it.
The main reason is that here we have a field of American life where I think we can say pretty clearly that meritocracy is not an important factor. Nothing is ever purely about anything, but corporate boards in the United States are about as close as it gets to a pure case of privilege reproducing privilege. The key criteria for serving on a corporate board is to seem like the kind of person who would serve on a corporate board—which is to say a white man of a certain age. But there are no actual job qualifications or performance criteria for nonexecutive directors. So the CEO of the Washington Post Company (Slate's parent) is on the board of Facebook, and Al Gore is on the board of Apple, and a former high-level BMW executive is on the board of Microsoft. Yet if you want to put women on your board, this very same open-endedness makes it easy. Maria Klawe, president of Harvey Mudd College, is also on the Microsoft board. And good for her.
Now my best guess is that women's underrepresentation on boards doesn't have huge practical consequences. There is some evidence that more diverse boards outperform less diverse ones, and probably some downstream gender-equity issues would get addressed better if firms had better gender equity on their boards.
But the lack of board diversity is important primarily because it's a huge tell—and not because it has huge consequences. A company that can't manage to have half its board seats filled with women simply isn't trying. Which is to say that the vast majority of large American companies simply aren't trying. And yet most of those countries would say they think diversity and gender equality are important. But given a fairly simple, straightforward, and low-consequence way of making a statement about gender equity, virtually no firms do it. Most other corporate staffing decisions are a good deal more complicated, and the barriers to gender inclusion may be more real or more robust. But when you see a corporate board that's not even close to half women—and nine times out of 10 that's what you'll see—you shouldn't trust any assurances you receive about anything else the company is doing.