I wish this were a joke, but it isn't.

If you want to be a successful woman, you can have any hair color you like. But if you crave a leadership position, such as elected office, CEO of a large company, or head of a prestigious organization, you should dye your hair blond if it isn't that color already.

Don't believe me? Statistics don't lie. Only 2 percent of the world's population has naturally blond hair. If you narrow your sample to white people in the United States, that percentage goes up, but only to 5 percent. But look at women in leadership positions and you'll see a lot of golden tresses. More than a third of female senators--35 percent--are blonde. And though the sample size for female CEOs of S&P 500 companies is admittedly small, 48 percent--nearly half--are blonde.

These statistics come from research by Jennifer Berdahl and Natalya Alonso, professors at the University of British Columbia's Sauder School of Business, who note that a disproportionate number of female university presidents are blonde as well. In fact, Berdahl writes in her blog, "This first became obvious to me at a conference at the Harvard Business School where the female speakers were mostly blonde."

Think of the women leaders who've smashed the glass ceiling in recent years. The first female Supreme Court justice? Sandra Day O'Connor. The first female presidential nominee of a major party? Hillary Clinton. It goes without saying that most of these women were not born blonde, but that doesn't seem to matter. No one in their right mind could have thought Geraldine Ferraro--the daughter of two Italian immigrants--could be a natural blonde, but she was not only a senator but also the first female vice presidential nominee of a major party.

Why do we prefer blondes?

What's going on here? Racial bias is part of the explanation--white people hold a disproportionate percentage of leadership roles when compared with the population in general. There's likely some youth bias as well, since many people are blond as children but have darker hair later in life. But it's noteworthy that this strong preference for blond hair doesn't extend to male leaders. For example, only 2 percent of male CEOs in the S&P 500 are blond. Nor does it extend to successful women in nonleadership roles--except, obviously, in entertainment.

What's fascinating is that we live in a society that is constantly telling us that blonde women are more attractive and friendlier but less intelligent or competent than everyone else. We've received this message in a steady barrage of Blondie cartoons, Marilyn Monroe movies, and dumb-blonde jokes.

That, Berdahl and Alonso say, is precisely the point. Women in positions of great authority are often caught in a bind. If they adopt a stereotypically female style--friendly, conciliatory, and nonconfrontational--they aren't seen as unfeminine, but they aren't respected as strong leaders either. If they adopt a more stereotypically male stance, being forceful and authoritative, they may be respected, but they risk being labeled as bitches or ball busters.

Every effective leader needs to be forceful and authoritative, though, at least some of the time. And it turns out that women in leadership positions who behave that way can blunt some of the criticism by sporting blonde hair, which signals that they're really soft, friendly, and not-so-smart underneath, even as they issue commands.

To test this theory, Alonso and Berdahl conducted a study of 100 men, to gauge their reactions to hair color. Asked to rate photos of blonde and brunette women on attractiveness, competence, and independence, the men thought all the women were equally attractive, but that the brunettes were more competent and independent.

Then they were given photos of blonde and brunette women paired with a quote, such as "My staff knows who's boss" or "I don't want there to be any ambiguity about who's in charge." Suddenly there were big differences, with the brunettes coming in for harsh criticism, while the blondes were rated much higher on warmth and attractiveness. As Berdahl told the Huffington Post, "The same woman changes her hair color from blonde to brunette, and she's seen as a bitch."

Why you should dye your own hair

Should we all be struggling against stereotypes like these? Of course we should. But if they ever go away it certainly won't be in the near future. And that's why smart women who want to be respected as leaders so often turn into blondes, Berdahl says. "If women are choosing to dye their hair blonde, there's something strategic about the choice," she explained to HuffPo. "If the package is feminine, disarming, and childlike, you can get away with more assertive, independent, and masculine behavior."

So go ahead--make that appointment with your hairdresser. We may want to change the world. But first we have to reach the positions that will let us do it.