In the original script writer Dan O'Bannon had focused on...

In the original script writer Dan O'Bannon had focused on writing the Alien first, putting off developing the characters for a later draft. Thus he and Ron Shusett had written all of the roles as generic male ones with a note in the script explicitly stating “The crew is unisex and all parts are interchangeable for men or women.” (x)

Alien (1979)