In a population entirely composed of solitary prey, the fitness payoff to individuals is P. But then mutant individuals arise that use others as living shields. When a solitary individual is found and used by a social type for protection, the solitary animal loses some fitness (B) to the social type. The costs (C) to social individuals include time spent searching for another individual to hide behind. We will assume that when two social individuals meet, each has an equal (1/2) chance of being the one to hind behind the other when a predator attacks.