The latter clusters were the clans, and they originated during the beginnings of the human family.

Every clan formed a group of supposed blood-relatives, looking back to a mythical or traditional common ancestor.

Descent from the mother being always plain, the clan claimed descent in the female line even if every recollection of the female ancestor were lost, and theoretically all the members of one clan were so many brothers and sisters.

This organization still exists in the majority of tribes; the members of one clan cannot intermarry, and, if all the women of a clan die, that clan dies out also, since there is nobody left to perpetuate it.

The tribe is in reality but a league; the clan is the unit.