This is necessary wherever organisms are living in large groups. The behaviour allows the social group to function without too much disruption. Social hierarchies are common, the pecking order of roosting chickens, is a good example of a dominance hierarchy which also occur in dogs, chimpanzees and humans too. The dominant individual in the social group generally obtains more food, mates with more members of the opposite sex and often is required to be the first to defend the group against attack. The dominant individual will have to defend it’s position from other members of the group which try to take over.