I've read that Alien was written with an explicitly gender-neutral script, and then the gender of each character was determined during casting by which actor they wanted for the part.

The net result was Ripley, one of the all-time models of a female action hero.

I don't know what (if anything) to make of that, other than "write people first and genders second, if at all," but it's a tidbit I always found very interesting.

-TG