Earlier this week, California Governor Jerry Brown signed a bill into law making his state the first in the nation to require the boards of publicly traded companies to include women.

The moves comes as, nationwide, the number of women in top corporate leadership positions is on the decline. The number of female CEOs of Fortune 500 companies declined by 25 percent this year.

Nancy Koehn, historian at the Harvard Business School and author of "Forged in Crisis: The Making of Five Courageous Leaders," said that for a long time the conventional wisdom around this issue was that the absence of women in corporate C-Suites was the result of a supply problem: in other words, that there were simply not enough qualified women available. That view is changing.

"The reasons behind this are now becoming much more nuanced and complicated than the original answer for years and years, which was: 'There's a pipeline problem,'" Koehn explained on Boston Public Radio. "That doesn't look like it's a very robust explanation any longer."

She continued, "Now we have to start talking about, what happens to very talented women at the top of the game? Why are they passed over? Why are they fired at the top of companies as many, many women are?"

Koehn believes that society's attitudes about gender, work and leadership contribute to why so many female leaders are able to rise through the ranks of their companies only to hit a glass ceiling at the very top. One example is the way self-promotional behavior in the workplace can often be perceived as aggressive from a woman but assertive from a man.

"You're portrayed as sometimes overly aggressive or overly ambitious," Koehn said. "A man would be lauded as ambitious and hard-charging and really, really working hard."