Joseph, Yassin, and their families, live on opposite sides of the Israeli-Palestinian divide. Joseph is the dreamy, artistic son of a high-ranking Israeli officer and a French-born doctor, emerging from a cozy, privileged adolescence and preparing for his own military service. A routine blood test shows that he cannot be his parents’ child, and further investigation reveals that their baby — Yassin, that is — has been reared by an Arab couple on the West Bank.

Although the story Ms. Lévy has to tell takes some surprising turns, the lessons of “The Other Son” are not hard to guess. The film is propelled by a hopeful, good-hearted humanism, and it sets out to show that, in spite of political, religious and cultural divisions, people are people.