A couple of years ago, I interviewed Kristen Wiig, who is something of a heroine of mine, and spent much of the time circling around a question that begged to be asked: how come an actor as brilliant as her is consigned to bit parts and lame roles? I didn't quite put it like that, but it's a question that regularly comes up with women actors and the answer is invariably the same. "It's not that there aren't good roles for women, there just aren't enough," Wiig replied, trying not to sound too whingey. She was, after all, promoting Paul, the blokey alien comedy in which she gamely played Simon Pegg's underwritten "love interest". But Wiig revealed she was taking matters into her own hands and writing a female-led comedy that played to her strengths, with her colleague Annie Mumolo. The rest is history – Bridesmaids grossed nearly $300m (£198m) worldwide, gave us Wiig admirers what we yearned for and showed the others what they had been missing.

In retrospect, it seems like a thuddingly obvious solution to the "there just aren't any decent roles" problem: write your own part. But for women, especially, it hasn't been that easy. The statistics are regularly invoked, but still pretty staggering: women make up just 18% of key behind-the-scenes roles in the movie industry. For writers, it's even lower: 15%. That translates into a great many casting calls for bikini-clad chainsaw victims, superhero support staff and obliging love interests. The unhealthy preponderance of female characters whose primary function is to guide the male protagonist out of his malaise throws into relief the fact that most movie representations of women are male constructs – and not all those males understand the opposite sex as intimately as their own. Some day, Nathan Rabin's identification of the "manic pixie dream girl" trope will be seen as the movie equivalent of isolating the polio virus. In the meantime, struggling actresses across Hollywood are tearing off their Zooey Deschanel wigs, crying: "What am I doing wrong?"

Ellen Page (left) and Brit Marling in The East

That's not to say men cannot write women or vice versa, but more and more actors are following Wiig's example, and cinema is better for it. A good example would be Brit Marling. As a screen presence, she is pretty much the polar opposite of the manic pixie dream girl: subtle, hypnotically serene and not given to prancing about in fountains. Dismayed by the parts Hollywood was offering, Marling engineered her own acting breakthrough by co-writing movies with her flatmates, both aspiring directors. The results – Another Earth, with Mike Cahill, and Sound of My Voice, with Zal Batmanglij – made her a breakout star at Sundance in 2011. More to the point, Marling's characters are refreshingly unorthodox. In the former, she is a reticent player in a twisted sci-fi romance; in the latter, she is an enigmatic cult leader who claims to be from the future.

In her latest film with Batmanglij, The East, Marling plays another atypical role: she is a conflicted corporate spy infiltrating an eco-terrorist cell – the sort of hero you would still expect to see played by Matt Damon, say, or Joseph Gordon-Levitt. None of Marling's writing efforts has been perfect, but they have put her on the map. She was then snapped up for the Richard Gere thriller Arbitrage and Robert Redford's The Company You Keep.

Coming at it from a very different direction is Greta Gerwig, star of the forthcoming Frances Ha. Directed by Noah Baumbach, and written by the two of them, it is a knowingly exuberant study of a dizzy New Yorker struggling with post-college maturity, which some have likened to a modern-day Annie Hall. Gerwig came to attention as an actor via the oft-maligned "mumblecore" movement, which espoused scriptless, naturalistic observation – also sometimes known as terminal self-indulgence. The films were largely improvised, and Gerwig was often credited as a co-writer, which could give the impression it was the same with Frances Ha.

Greta Gerwig in Frances Ha (2012). Photograph: Capital Pictures

In other words, Gerwig did her stuff in front of the camera, Baumbach shaped the footage and they split the writing credit. In fact, the two of them co-developed the movie more collaboratively, emailing back and forth notes and suggestions about the character. Baumbach is one of the few indie auteurs out there who is not afraid to let in a little female influence. His previous movie, Greenberg (which also starred Gerwig), was co-written with his wife at the time, Jennifer Jason Leigh. In the process of making Frances Ha, he and Gerwig became a couple. They are making another movie together and are co-writing a family animation.

Understandably, Gerwig has bristled at being described as Baumbach's "muse". "I'm OK with the term muse as long as you acknowledge the muse wrote the script, too," she told a recent interviewer. "I feel like I'm the loudest muse that the world has ever seen." In the past, it was accepted without question that a woman's place in the creative process was as a mute, passive influence on the male artist's roiling intellect – a creaky classical idea that didn't date quickly enough for cinema to escape it. You could characterise a great many auteur-actress relationships in muse terms: Josef von Sternberg and Marlene Dietrich; Michelangelo Antonioni and Monica Vitti; John Cassavetes and Gena Rowlands; Alfred Hitchcock and Grace Kelly/Tippi Hedren. Not to mention two of Frances Ha's greatest influences: Jean-Luc Godard, who cast his wife Anna Karina in eight of his 1960s films, and Woody Allen, who has spent much of his career writing with a significant female actor in mind: Diane Keaton, Mia Farrow, Scarlett Johansson, and even, in To Rome with Love, Gerwig. "I never used to be able to create parts for women," Allen told W magazine two years ago. "But then I met Diane Keaton, and we started dating and moved in together, and I started writing for her."

Alice Lowe in Sightseers, which she co-wrote, with fellow star Steve Oram

Thanks to female screenwriters, we have had a fresh perspective on this vaunted masculine creativity recently. First, there was last year's delectable Sightseers, co-written and co-starring Alice Lowe. Her simple-minded character, Tina, relishes the prospect of playing muse to her homicidal partner and wannabe writer Chris: "There's something in me, Tina," he says. "I'll help you squeeze it out," she coos. But as the couple progress on their murderous tour of the Peak District, Tina becomes less and less passive. By the end, he has become her muse, and he doesn't like it.

And special mention must go to Ruby Sparks, in which Zoe Kazan's eponymous character magically springs from the imagination of a blocked, self-absorbed novelist (Paul Dano, her real-life partner). Ruby is kooky, creative, and sexually compliant. She jumps in swimming pools with her clothes on, loves watching zombie movies, and does all the cooking. In short, she is a parody of a manic pixie dream girl. And anything Dano doesn't like about her, he can simply change with his typewriter. Except it's Kazan who is really pulling the strings – she wrote the movie. Ruby Sparks was rather too hastily dismissed as a quirky romcom, when in fact it is a sly, intelligent commentary on men controlling women – in love, in fiction and in film-making. Ruby is, after all, a woman who must behave as she is written, just as actors do for a living, readjusting their character obligingly with each script rewrite. By channelling those frustrations into her own script, Kazan took back control, and gave herself a peach of a role in the process.

Zoe Kazan and Paul Dano in Ruby Sparks: Kazan's character is a parody of the 'manic pixie dream girl'

Why is this happening now? It's not just down to Bridesmaids. Or Lena Dunham, whom it is obligatory to mention when discussing this topic, even though she is mainly in television. Female screenwriters may have been outnumbered in the industry, but they have always been there, even if it took until 1991 for a solo woman to win the best original screenplay Oscar (Callie Khouri for Thelma & Louise). The history of female directors who write has been a happier story. But until recently, actors writing for themselves was somehow a leap too far.

Even for a shining light such as Julie Delpy, who co-wrote the last two of Richard Linklater's magnificent Before Sunrise/Sunset/Midnight trilogy, as well as her own movies such as 2 Days in New York and 2 Days in Paris. When she was in her 20s, nobody would produce any of her screenplays, she says. Her agent even fired her when she chose to write Before Sunset rather than going for "sexy Latina parts" in Hollywood movies.

The tools of film-making are more widely available today, though, and it has become easier for both men and women to be multidisciplinary. So now you get figures such as Katie Aselton, who wrote, directed and starred in Black Rock – a sort of feminist Deliverance. Or the actor Lake Bell, whose voiceover artist comedy In A World … is coming soon (Bell wrote, directed and starred. She is also "automotive contributing editor" for the Hollywood Reporter – talk about multi-talented). Or Parks and Recreation star Rashida Jones, who co-wrote and starred in last year's Celeste and Jesse Forever. Or even Sarah Polley, who has practically given up acting to write and direct others, including her own family in her current documentary Stories We Tell.

Despite the statistics, maybe the barriers to entry are no longer as high as everyone assumed – unless you are a young man with a story about a crazy, free-spirited girl who inspired you to love life anew.