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Marissa Mayer and the masculine requirements for success

July 23, 2012, 3:09 PM UTC

FORTUNE — Despite all the gains that women in business have made over the past several decades, one thing doesn’t seem to change: success still feels like a man’s game, even when women attain it.

Whether it’s dressing in the tradition of the successful man or leading in the style of other successful men — when alternate approaches might be just as useful — the idea is the same: without alternatives, true success in business will always be coupled with masculinity.

The idea that embracing femininity can go hand-in-hand with success in business can seem odd, particularly for members of the younger generation. The mothers of Generation Y were educated in a starkly different world. In 1960, 39% of undergraduates were women — while today, more than half are. And while many women have made significant achievements in business, many are doing it without the benefit of having mothers who could model the behaviors and choices of a successful businesswoman.

The reactions to Marissa Mayer’s recent appointment as Yahoo’s (YHOO) CEO — along with her announcement to Fortune’s Pattie Sellers on Monday that she is the first Fortune 500 CEO to accept the position while pregnant — raise a question that rings in many female professionals’ ears: Why should Mayer’s femininity even matter?

MORE: Yahoo’s Mayer: “having it all” debate rages on

At 37, Mayer is the youngest CEO in the Fortune 500. As a manager at Google, she was both loved and hated for her autocratic style. She works insane hours and still finds time for an active social life. She’s a self-proclaimed geek, who also happens to love designer threads. Her seemingly superhuman tendencies may be hard to fathom (or emulate), yet Mayer has remained true to herself and never apologized for them.

“One of the things I care a lot about is helping to… show girls that you can be feminine, you can like the things that girls like, but you can also be really good at technology,” Mayer told the Daily Beast in 2010. For many Gen Y women, Mayer’s example is one our mothers couldn’t demonstrate: a successful woman in business who fully owns her femininity.

As the first woman in my family to attend college, I had no female model of professional success on hand to use as a guidepost. In my young mind, to be professionally credible meant you had to act masculine.

When I graduated from college and joined McKinsey and Co.’s New York office in 2008, building my professional presence was critical — and like so many tests, this one was timed. The unspoken need to demonstrate professional decorum while trying to thrive in a fiercely competitive environment was reflected externally for women through our wardrobe choices. The pressure to showcase my competence both through my work and my personal style rendered me even less sure of where the real me, a fashion-loving, baby-faced woman of Middle Eastern and South American descent, fit in to the picture.

MORE: Fortune 500 Women CEOs hits a record 19

My time at McKinsey made it clear that there was a dearth of female business leaders who were comfortable with their femininity, as women’s clothes seemed to progressively lose form and color and their hair would lose length and shape as they ascended the ranks. Did high-achieving women make themselves more masculine on purpose? Or were they just tired of being different and let go of the characteristics that set them apart?

Women can change these perceptions by expressing their individuality (as many, including Mayer, already have) not by trying to make their images more digestible to their peers. Deviating from our preferences, and losing our respect for those preferences, to climb the ladder validates a very noxious idea: that success comes in one basic shape and form.

Mayer hasn’t asked anyone to emulate her leadership or runway style. She also hasn’t asked anyone to follow suit and cut their own maternity leaves short. She is a role model for young women – not because of her individual choices, but because she does what works for her, femininity and all. And that kind of attitude is what will help redefine success for women, one that we should welcome.

Caroline Ghosn co-founded The Levo League with Amanda Pouchot.