In the few days since Marissa Mayer’s baby arrived, I’ve watched the resurgence — again — of the debate about working parenthood, maternity leaves, and even “baby bumps.” I have mixed feelings about this.

Mayer’s situation is extremely unusual. A short maternity leave may be relatively easy for her, in part because she and her spouse have great wealth and because, as CEO, Mayer has considerable discretion about how to spend her time. This is not the case for most working women — or for most working men.

And yet, that the board agreed to hire a pregnant Mayer as CEO was a sign of real progress in our collective grasp of what’s possible, for men and for women. The decisions made by Yahoo’s board and by Mayer signal something important to us all — greater freedom. This episode in our social history is but one highly visible example of the many new options available to people as they aim to pursue lives that fit with their most precious values. Mayer made her choice, and that she was able to do so is not just because of her financial wherewithal, it’s also because her choice is now socially and culturally legitimate. Even five years ago it would not have been.

We’re going to see more new possibilities, if my research on Wharton students (part of the Wharton Work/Life Integration Project) is any indication. In 1992 we surveyed over 450 Wharton students, at the moment they graduated. Then, this past May, we asked the same set of questions of the Wharton undergraduates in the Class of 2012. In part, the surveys explored attitudes about two-career relationships. We asked students to what extent they agreed with these two statements:

Two-career relationships work best when one partner is more advanced than the other.

Two-career relationships work best when one partner is less involved in his/her career.

In 1992, men were much more likely to agree with both these statements than were women. Our preliminary analyses show that in 2012, however, there is a convergence of attitudes about two-career relationships: Men are less likely to agree with those statements than they were 20 years ago, but women are now more likely to agree; both have changed. Compared to graduates 20 years ago, young men graduating today are more egalitarian in their views and women are less so, perhaps because they are more realistic.

Men and women today are more likely than the previous generation to share the same values about what it takes to make dual-career relationships work. One implication of this finding is that there is greater solidarity among men and women and therefore more flexibility about the roles that both men and women can legitimately take in society. There is now a greater sense of shared responsibility for domestic life. Young men are realizing they have to do more at home than their fathers did, and today’s young men want to do so. Ellen Galinsky’s research on the “new male mystique” affirms this trend.

Our survey also asked men and women to indicate how strongly they agree with these statements:

It is easier for men to combine the demands of work and family.

Pursuing a demanding career will make it difficult for me to be an attentive spouse or parent.

In 1992, we saw no difference between men and women in the way they answered those questions, but in 2012 we find that women are more likely than men to agree with those statements. Again, women today have a less sanguine view of what’s possible. How can this be good news?

While it used to be that women had aspirations for hierarchical advancement that were lower than those held by young men, today those aspirations are the same for men and women. But now women’s family ambitions (if we can call them that) are lower than they were 20 years ago; that is, in 1992 79% of women graduating from Wharton said they definitely planned to have children, while in 2012 only 42% made this claim. There is now greater awareness of constraints, and expectations are being adjusted accordingly. Sounds like a reduction in freedom, right? But perhaps, with a more clear-eyed vision of what is to come — and with men and women holding more aligned views about the value of work and parenting — people will take more focused, concerted action to chip away at the established order and more successfully pursue new options.

Marissa Mayer is just one very fortunate person. But as a simultaneous new CEO and new mother, she represents something more — a new prospect of what is possible. That her choice is available to her doesn’t mean, of course, that such possibilities are now here for all. But her choice is real. We are at the cusp of the emergence of new models. Young people will increasingly be active in carefully, consciously, and deliberately crafting their roles.

Attitudes are changing. Yes, it remains incredibly difficult for women to break through to the top strata, because it’s still primarily a man’s world at the most senior levels and because there are all kinds of additional burdens that women continue to carry. And yes, it still remains difficult, though increasingly possible, for men to opt for the non-traditional path of stay-at-home-dad.

But we are seeing more expressed freedom, more realistic goals, and more unity among young men and women as they are creating new ways to pursue lives that fit with who they truly want to be. And that is a good thing.