Okay, this is freaking awesome so I had to share it. Our species (and others) need a large group to survive either for protection against opposing factions, predators or to group hunt/gather.
We come to a problem.
How do you keep a group from breaking apart because of fights, quarrels and competition for limited resources or mates?
Solution: have a hierarchy, a pecking order.
Exemplified in chimpanzees, this hierarchy is mediated by an alpha male that steps in and breaks up fights between various parties. To have a single character representing the "final say" in arbitration is the easiest (and some times most effective) way of maintaining order. Furthermore, their authority is most widely respected when it is impartial and doesn't side with those most likely to benefit themselves (like through reciprocity).
Key-->not only could this have been how leadership could have evolved (through a necessary stabilizing force in large groups), but also could be how our since of equity, justice and community concern could have evolved. We needed to be able as leaders or subordinates to know how to effectively take sides with equity/justice instead of a party, which would only perpetuate the division.
The added benefit for the leader male could have been that through this mediation role he could have forced out other males from becoming next in line for alpha status.
I love this sh*%$. That is awesome.