What is the practical purpose of a low-cut leather catsuit? This I have pondered, too. Should I be wearing one? Should we all?

Like many fans with too much time on their hands, I devoted a sum-total of 45 catatonic hours preparing for the arrival of “Avengers: Endgame” by rewatching all previous 21 movies in the Marvel Cinematic Universe.

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Condensing the most sweeping pop cultural movement of the past decade into a few weeks reveals a lot about how far we’ve come. On screen as well as off.

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Consider, for example, a scene in the original “Iron Man,” released just 11 years ago, which is suddenly an eon in terms of our comprehension of sexual harassment. Robert Downey Jr. as billionaire Tony Stark invites his assistant to dance at a company event. “Am I making you uncomfortable?” he asks. Yes, Pepper Potts acknowledges — it is weird to dance with her boss in a backless dress while an entire ballroomful of guests watches. “Well, you look great, you smell great,” he responds. “But I could fire you if that would take the edge off.”

It’s meant as a joke, and it’s part of their dynamic: She’s the organized worrywart, he’s the quippy playboy. When I watched this scene in the theater in 2008 — well, I don’t even remember noticing it. At the time, nothing seemed strange about a boss suggesting his underling’s career could be axed if that would get them in bed faster.

Consider, for example, “Iron Man 2” in 2010, when Tony wants to hire Scarlett Johansson’s character only because she looks like Scarlett Johansson, and Pepper tries to block her hiring only because she looks like Scarlett Johansson . . . and, honestly, it’s hard to determine which behavior is worse.

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So imagine the joy, then, of “Avengers: Age of Ultron,” which came out in 2015. Pepper Potts is now the head of Stark Industries. And Scarlett Johansson, i.e. Black Widow, has not only a healthy platonic friendship with her male colleague Hawkeye but also a friendship with his wife and kids. Sexy female assassins don’t necessarily have designs on your husband; sometimes they’re just Auntie Assassin.

I mentioned all of this to some smart friends whose Avengers knowledge borders on obsessive. They helpfully responded with a barrage of articles: A list of the most feminist movies in the Marvel universe. A story about the creative influence of Marvel chairman Ike Perlmutter, who reportedly cut back on Black Widow merchandise because he didn’t think “girl” superhero products would sell — and what changed after a revamped corporate structure curtailed Perlmutter’s power.

It was all useful context for understanding how the sausage of pop culture is made. But it didn’t really address what I was trying to get at. What I was trying to get at was the emotional experience of watching a decade fly by, commercial-free, via Netflix and Amazon, and seeing things progressively suck a little bit less. Of watching the conversations America was having — about representation, about women in the workforce or the military, about equality in romantic relationships — be interpreted onto the big screen.

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In “Ant-Man” (2015), Hope Van Dyne discovers her father has finally made a superhero suit for her so she can be more than Paul Rudd’s trainer: “It’s about damn time,” she says.

A trio of female characters in “Black Panther” (2018) — Nakia, Okoye and Shuri — fight battles and solve critical problems in a story line that assumes nothing unusual about women being a country’s top scientist or general.

In “Avengers: Infinity War” (2018), a villain arrives on the battlefield and purrs that she’s caught Scarlet Witch “all alone.” But then suddenly two more female characters arrive, weapons ready. “She’s not alone,” one says, and they all proceed to take care of business.

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This happened, and the theater in which I saw it erupted in cheers. Apparently, I don’t remember watching Tony Stark threaten to fire his assistant, but I’ll remember when a packed audience lost their minds at the novelty of this fight scene: It had taken 19 movies, but finally there was a screenful of competent woman warriors all working together.

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But that’s what progress looks like, isn’t it? Sometimes when we’re in the dark ages, we don’t realize we’re there. We let things wash over us. We don’t realize when the jokes are bad, or the balance is off, or that we’ve sat through scene after scene of interesting characters engaging with each other, and it’s great, except that all of them are men.

We realize when things change, though. When, year by year or movie by movie, someone tweaks the story. “Endgame” will come out and will make a bazillion dollars and will break box-office records and will be a cinematic triumph a decade in the making. And me? I’ll appreciate it for all of those reasons. But I’ll also appreciate that when the Marvel Cinematic Universe expanded, it did so in a way that included everyone.