The silverback is the center of the troop's attention, making all the decisions, mediating conflicts, determining the movements of the group, leading the others to feeding sites, and taking responsibility for the safety and well-being of the troop. Younger males subordinate to the silverback, known as blackbacks, may serve as backup protection. Blackbacks are aged between 8 and 12 years and lack the silver back hair. The bond that a silverback has with his females forms the core of gorilla social life. Bonds between them are maintained by grooming and staying close together. Females form strong relationships with males to gain mating opportunities and protection from predators and infanticidal outside males. However, aggressive behaviours between males and females do occur, but rarely lead to serious injury. Relationships between females may vary. Maternally related females in a troop tend to be friendly towards each other and associate closely. Otherwise, females have few friendly encounters and commonly act aggressively towards each other.