We present a game theoretic model to explain why people form life long monogamous families.
Three components are essential in our framework, paternal investment, fatherhood
uncertainty, and, perhaps the most distinctive feature of all, the overlap of children of different
ages. When all three conditions are present, monogamy is the most efficient form of
sexual organization in the sense that it yields greater survivorship than serial monogamy,
group marriage, and polygyny. Monogamy is also the only configuration that fosters altruistic
ties among siblings. Finally, our result sheds light to the understanding of why
most religions center around the monogamous fidelity family