When you start learning about costume design, you get to know everything!!!! YAY!
Back in the day (that'd be the 1960s), Star Trek put mini-skirts on all the women. At the time, men forced "nice women" to wear long skirts (which covered the knees) or dresses, and the mini-skirt was seen as liberating.
But just 10 years later, as Star Trek: The Motion Picture went into production, the mini-skirt was seen as sexist because it was seen as sexualizing the professional woman. So director Robert Wise and costume designer Robert Fletcher got rid of it in favor of a unisex uniform that put women in pants. Even when the uniform underwent a significant change in Star Trek: The Wrath of Khan, the unisex uniform was retained.
The unisex uniform was retained in Star Trek: The Next Generation and Star Trek: Deep Space Nine. However, in the DSN episode "Trials and Tribblations", Lt. Dax has to wear a mini-skirt to fit in with the 1960s-era show. Her comment? "Women wore less in those days."
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Director J.J. Abrams had a problem in Star Trek (2009). He wanted to return to The Original Series, with its primary-color costumes and mini-skirts, but he also didn't want to take broadsides from feminists who would have called for his head had he sexualized women.
Abrams hired costume designer Michael Kaplan to work on the film. Kaplan had never seen any Star Trek film, although he was a little familiar with TOS. Kaplan won a BAFTA for his work on Blade Runner, and had been nominated for Costume Designers Guild Awards for his work on Fight Club (1999) and Mr. & Mrs. Smith (2005) . He'd be nominated again for Star Trek (2009).
For Star Trek and Star Trek Into Darkness, Kaplan returned to the original mini-skirt design, arguing that it could not be simply abandoned. However, he lowered the skirt slightly so that it would not ride up so much when the women sat down and would not reveal the buttocks as so often happened whenever there was a light breeze on TOS.
Roberto Orci and Alex Kurtzman worked hard to get Uhura out of her communications chair and into the real world. However, they couldn't get her out of the mini-skirt. Uhura is seen in a mini-skirt in the Iowa bar where Kirk gets into a fight, at Starfleet Academy, and on the Enterprise. All the women's costumes in the first film show women with bare arms, while men remain firmly and completely clothed.
For the second film, Orci, Kurtzman, and now Damon Lindelof worked to get Uhura and other women into less sexual costumes. One attempt failed: During the flight over the volcano, Uhura is shown in a skintight catsuit that no man was forced to wear. And although Uhura is still seen in her mini-skirt, she spends a great deal of time in a informal clothing consisting of pants, shirt, and jacket (Klingon) and in a more TNG-like grey unisex uniform aboard the Enterprise.
The same holds true for Alice Eve, who plays Dr. Carol Marcus. She's put in a mini-skirt for her shipboard scenes, but she wears a full-body, somewhat clunky dress uniform when she first meets Kirk and she has the standard unisex grey uniform for her appearance on the planetoid with the torpedo and Dr. McCoy.