Why did the first Africans live together in extended familiesor age-set groups?

The early humanoids living in Africa lived together in extended family groups because they were genetically programmed that way. And for good reason, too. At the time they were at the same time predators and prey animals. They were usually slower and weaker than animals that preyed on them and slower than many animals that they hunted themselves. Living on ground level made them extra vulnerable. So living in groups made for mutual protection and for cooperation to hunt faster animals.
They did not live, but only went out hunting in age-set groups because hunting took a lot of stamina and physical power and again, hunting in groups gave a much better chance of succes.