Comedyevolves. We long ago bid adieu to the physical acrobatics ofBuster Keaton, the wisecracks of Bob Hope, the witty repartee of Cary Grant and Irene Dunne. The now-reigning comedy of embarrassment, seen in the films of Judd Apatow and the Farrelly Brothers and all the loss-of-virginity farces, seems particularly appealing to younger viewers, who can relate to the awkward silences of crushes, being stuck with someone who is clearly physically undesirable, or being oneself the nerdy companion of some repulsed hottie, that power imbalance being the kernel of the jest — though by the final credits, said nerd usually ends up with said hottie. Lena Dunham’s work is related to this mainstream comedy of embarrassment, but she takes it one bold step further, producing a much more subtle and sophisticated comedy of chagrin. And in Dunham’s world, there is no happy ending, only an enlightened realism.