Anger is one of the basic human emotions, as elemental as happiness, sadness, anxiety, or disgust. These emotions are tied to basic survival and were honed over the 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 norms.