Dominance and hierarchy are found throughout the animal kingdom. It is often seen in co-operative breeders, where one male and one female from each group do most if not all of the breeding. The submissive members of the group help to raise the young by helping with foraging and defense of the young. A good example of this kind of breeding is wolves (Canis lupus). They group into packs with a dominant pair. The entire pack helps hunt for food, care for young and defend territory from outside wolves or packs (Peterson 1984). The pack will work it's way across it's range, but not always staying completely inside it's territory (Joslin 1967). Wolves also have a well-studied and defined social order. Because of the nature of the hierarchy, there will inevitably be conflict between members of the pack, because the dominant wolf will try to keep the other wolves in their submissive position, and the submissive wolves will eventually want to reproduce, so it leaves them with two choices, leave the pack and attempt to start their own pack, or challenge the current dominant wolf for control of the pack. There is also the possibility that the dominant male could die, and in which case one of the other wolves of the same sex would then "move-up" to become the dominant wolf.
Until recently, another possibility existed, but had yet to be explored. What would happen if all the individuals of one sex (male or female) were somehow killed at the same time? Only with the recent jump in technology was this type of takeover able to be observed, and then it was only seen from satellite telemetry, so the specific behaviors associated with an outside wolf coming in and taking over a pack were not observed. However, it is now known that packs that lose all members of the same sex simply do not fall apart, they find a replacement, but the behaviors associated with the acceptance of the new dominant individual were not known.