I was in New York City last week in a movie theatre listening to roars of laughter as the audience watched the lesbian movie that is changing social history, The Kids Are All Right. When the lights went up at the end I saw that the packed cinema was full of straight guys with their girlfriends, I know this because as the line filed out there was a lot of hand-holding and kissing, probably an unconscious but necessary display of heterosexuality. The last time I saw the same mass-movement body language was after Ang Lee’s Brokeback Mountain, the gay cowboy movie.

In both cases I think that the guys were looking for reassurance as much as making a statement. If gay is the new normal, where does that leave straight? Lisa Cholodenko’s movie is a family comedy with a twist, the parents are both women, the kids charmingly call them “the mumses” and the kids were conceived using a sperm donor.

The family is well-off middle class, with a detached house and a Volvo. Annette Bening plays Nic, a doctor, who supports the family. Julianne Moore plays Jules, the sweet sexy softer half, who has never quite got her career together. The plot spins round the classic theme of the stranger, the newcomer who disrupts the status quo, so leaving everybody to reassess and maybe, or maybe not, remake their lives.

The stranger in this movie turns out to be the kids’ biological father, Paul, contacted through the sperm-bank by the daughter, Joni, 18, and son, Lazer, 15. They don’t tell the mumses until Nic decides that Lazer must be gay and having a relationship with someone called Paul, the mysterious “other” on his mobile phone.

When Lazer asks his dad why he decided to be a sperm donor, the laid-back ladies’ man Paul (played by Mark Ruffalo) replies: “It was more fun than giving blood.”

Lines such as that raise roars of laughter from the men in the audience, and every guy is going to identify with Paul’s easy sexuality and magnetic attraction. He has n...