25 Things You Didn't Know About Alien
12. Not A Single Character's Sex Was Predetermined By The Script
When writing the script, Dan O'Bannon and Ronald Shusett included a clause indicating that all the characters were "unisex", meaning that they could be cast with either men or women. This allowed them to write the script without any preconceptions about gender roles and any limitations they might impose.
This explains why throughout the entire film, the characters only ever refer to one another by their surnames, with their first names not revealed until the inquest into the Nostromo incident early on in Aliens. However, one particular character was always intended to be male...