Why do birds often live in pairs and rear chicks together, whereas female mammals usually live in groups and rear their young without male help? Why do males sometimes live with a single mate when they are capable of fertilizing more than one female's eggs? Is male helping behavior important for monogamous partnerships? This book provides answers concerning the biological roots of social monogamy in animal groups as diverse as ungulates, carnivores, rodents, birds and primates (including humans) for students and researchers in behavioral ecology, evolutionary anthropology and zoology.