When the population of a family reaches a certain level (for example, 10 people or 15 people or even more), give them a reward~~~
A strong man will be born! He can run faster than others that he can catch the “bad” guy. (kinds of polices)~~the "bad” guy can not move in 5-10 minutes as a punishment.
Then the strong man can tell the families what happened and let them decide whether to vote (the strong man have no voting right, coz he’s strong…)
Just a simple idea…
Or
The reward turns into that each person gets a like ticket, and the person who collects X like tickets can become the person with ability(run faster, can catch people) in 10 minutes… mess