The percentage of women majoring in computer science dropped off sharply starting in 1984, even as it rose in fields like medicine, the physical sciences, and law. What explains that mysterious inflection?

A recent episode of Planet Money investigated.

The share of women in computer science started falling at roughly the same moment when personal computers started showing up in U.S. homes in significant numbers.

These early personal computers weren't much more than toys. You could play pong or simple shooting games, maybe do some word processing. And these toys were marketed almost entirely to men and boys.

This idea that computers are for boys became a narrative. It became the story we told ourselves about the computing revolution. It helped define who geeks were, and it created techie culture.

Movies like Weird Science, Revenge of the Nerds and War Games all came out in the '80s. And the plot summaries are almost interchangeable: awkward geek boy genius uses tech savvy to triumph over adversity and win the girl.

The episode is short, well worth a listen, and it does not come to any firm conclusions. However, the hypothesis resonates with me. As most adults are well too aware, often with great regret later in life, decisions made in childhood have great ripple effects throughout one's life. Early route selection can greatly influence path dependent outcomes, and careers are very path dependent. Recall the data from Malcolm Gladwell's Outliers about how children born in certain months were overrepresented in youth all-star hockey and soccer teams because they had a few months of physical development on their peers and thus received special coaching that created a virtuous cycle of skill advantage.

As an example, the Planet Money podcast recounts the story of Patricia Ordóñez, a young math wiz who nonetheless found herself behind other male students in computer science because they had all grown up with computers at home while she had not.

So when Ordóñez got to Johns Hopkins University in the '80s, she figured she would study computer science or electrical engineering. Then she took her first intro class — and found that most of her male classmates were way ahead of her because they'd grown up playing with computers.

"I remember this one time I asked a question and the professor stopped and looked at me and said, 'You should know that by now,' " she recalls. "And I thought 'I am never going to excel.' "

In the '70s, that never would have happened: Professors in intro classes assumed their students came in with no experience. But by the '80s, that had changed.

Ordóñez got through the class but earned the first C of her life. She eventually dropped the program and majored in foreign languages.

The story has a happy ending as she eventually got her PhD in computer science, but how many women like Ordóñez were casualties of all sorts of early life nudges away from computers?

My nieces all love Frozen, they all have Elsa dresses and Princess Sophia costumes, and they look adorable in them. But why are almost all Disney heroines princesses? I've written before about why, if I had daughters, I'd start them on Miyazaki over Disney animated movies, but given Disney's distribution power that may be a lost cause.

Sure, it might feel a bit odd, in the beginning, if commercials like this or this depicted young girls hacking on computers instead of boys. That's exactly the point, though. Those commercials took a gender role that would not have been strange prior to 1984—girls programming computers—and made it culturally bizarre, and we're still trying to undo the sexism two decades later.