In the animal kingdom not all matriarchal groups allow every female to mate, from http://www.doublexscience.org/dominants-...thers-day/
If this was how Keeper families worked then it would explain why some young females and perhaps males leave their family group.
Quote:Meerkats: Meerkat societies are highly structured, with a complex ranking system based on dominance. If you want to get ahead in the meerkat world, perfect the art of chin swiping and hip checking, practiced on those lower down the totem pole while someone more powerful than you is looking the other way. Being on top has its rewards; alpha female meerkats are the only ones who get to mate in meerkat town. A matriarch chooses her partner, who becomes the dominant (and only mating) male. Males initiate copulation by ritually grooming the female until she submits. If the matriarch tires of her partner, he’s quickly deposed by beta males who are more than eager to earn a chance at mating. Alpha females make all the decisions in the group: where to sleep, where to burrow, when to go outside, when to forage. Like bees, meerkat females are typically mother to all the pups in the group (females typically kill pups born of unsanctioned unions). In addition to being free to engage in mating, being a matriarchal meerkat comes with free baby-sitting and nursemaid service from the subordinate females (who also will lactate to feed her pups). The downside is that all the other females want your job; as they get older, the young females start hip-checking, stealing food, and even picking fights. Often, the alpha kicks young competitors out of the group before they get old enough to pose a threat.
If this was how Keeper families worked then it would explain why some young females and perhaps males leave their family group.