What are two reasons that Bruce belived that the Motilones were the fastest example of development that had ever occurred in a primitive tribe?

Many consider that the Motilones to be the fastest example of development that has ever occurred in a primitive tribe. Bruce believes that the first reason is because the Motilones are not asked to give up their culture and become white people. Every change is introduced based on things they already know. The second reason, Bruce believes, is because of the Holy Spirit. Without it, Bruce believes, that there can be not lasting change or development.