Paleolithic man formed groups because they were mainly hunters and food gatherers who use to catch prey and share among themselves. They did not know the idea of living a family life.
The life of such a group was different from modern days. They depended on nature for their livelihood. They collected fruits and hunted animals. They had no idea of cultivation and family life. They hunted animals with their crude stone tools and eat the meat. They did not know how to domesticate animals.