About 100,000 years ago the conditions of the planet were more rude. The earthly environment was not like today. There were beasts, natural traps like precipices etc. The man needed to hunt, search for water and live in caves. Obviously, there were no doctors, drugs etc. So, the men needed to stay together if no would die early. There were no wars or clan fights. Only when the first civilizations emerged was that started the wars. Humanity was more united.