Elephants exhibit herding behavior. when they travel, the oldest and largest members often travel on the outer edges of the group. why is this important to the survival of the species?

Elephants do not have many offspring, therefore they need to protect them from predators, by the older and larger members of the herd travelling on the outer edges, the young are more protected from being hunted by predators. This is not a means to enhance mating or about food, it is also not just a mere method of organizing themselves either; by travelling this way they protect the survival of the herd and species as a whole.