A pack (wolves): The first 3 are the older or sick and they set the pace of the group. If it was on the contrary, they would be left behind and lost contact with the pack. In ambush case they would be sacrificed.
The following are the 5 strongest. In the center follow the remaining members of the pack, and at the end of the group the other 5 stronger.
Last, alone, follows the alpha wolf. It controls everything from the rear.
That position can control the whole group, decide the direction to follow and anticipate the attacks of opponents. The pack follows the rhythm of the elders and the head of the command that imposes the spirit of mutual help not leaving anyone behind.