A macro-evolutionary theory of income inequality is proposed that is based on a society’s dynamic income generating process. Two types of processes are distinguished, namely dispersing and concentrating ones. A basic result shows that dispersing processes provide a selective advantage for stronger and more balanced interaction inducing more income equality and a non-stratified society; whereas concentrating ones favor weaker and less balanced interaction inducing less equality and a possibly stratified society. Also, more equal societies exhibit a higher degree of income mobility and are more resilient in the sense of being quicker to recover from shocks and to return to steady state than less equal ones. Stylized examples of pre-modern and modern societies are briefly discussed.