Anger is one of the basic human emotions, as elemental as happiness, sadness, anxiety, and disgust. These emotions are tied to basic survival and were honed over the long course of human history. Anger is related to the “fight, flight, or freeze” response of the sympathetic nervous system; it prepares humans to fight.
But fighting doesn't necessarily mean throwing punches; it might motivate communities to combat injustice by changing laws or enforcing new behavioral norms. Of course, anger too easily or frequently mobilized can undermine relationships and it is deleterious to bodies in the long term. Prolonged release of the stress hormones that accompany anger can destroy neurons in areas of the brain associated with judgment and short-term memory, and it can weaken the immune system.