A Fourth of July backyard barbecue is the setting for Rebecca Gilman's new play, "The Crowd You're in With", a funny, thought-provoking, ultimately disquieting exploration of the question of whether to have children. Melinda and Jasper, the hosts, are deeply divided by the issue; Tom and Karen, their landlords, decided long ago to remain childless; Windsong and her husband, Dan, are expecting a baby. As the play progresses, the motivations of these characters reveal themselves as ever more complex. Even as the characters often speak in very practical terms about their decisions, Gilman never loses sight of the mystery underlying a life-shaping decision guided by both rational thought and biological imperative, which ultimately speaks to the even larger question of free will and determinism faced by every person.