Anthropologists have studied hunter gatherer tribes for a long time and it is not as simple as those with the most confidence becomes leaders. For example, among the San people tribe leadership is shared by the elders. And anyone can become an elder by surviving til old age. In day to day tasks, such as during hunting, who leads the hunt is determined on a rotating schedule so that all men get to lead it from time to time.
Designated leaders probably didn't become the norm until about 4000 bc when early civilizations arose.
Another interesting tidbit noted by many anthropologists is that boasting is strictly forbidden. E.g if a tribesman catches a big prey, he must be humble and can not brag about how good of a hunter he is. It is different from the Western World, in which bragging is expected and necessary for leaders (case in point: Trump).