The study about the difference in how religious and secular communities survived based on how many constraints they put on their numbers makes sense. The reason given about seeming arbitrariness makes sense as a way of explanation. In my own experience I have little desire to follow rules I do not agree with if they are made by secular authorities, whether professors, lawmakers, or employers. However, if a priest, writer in the New Testament of the Bible or the Catholic Catechism instructs that some actions are to be taken and other actions are not to be taken I am much more receptive to obeying even if I do not completely agree with the idea myself.
The results that show that imposing restraint on members works for religious groups also should work on the idea that people that join religious groups are looking more for being better people on the inside and are willing to change their behaviors if that will help them.
However, I did find the idea that religion arose to help bind communities together utterly reductionist. I do not believe that using materialist ideological methods of studying religion can tell someone the purpose of the religion. All that is said is that a positive benefit of religion is somehow the sole reason for the religion.
Also I am not surprised that communism works in small Christian communities. It has a history of working since the 1st Century CE and is similar in practice to what monasteries have used as economic practice. “Each according to his needs and from each according to his abilities” has many problems in a large society where people do not know and trust each other. But shrink the community to where the members are already committed to not be free loaders and the central powers personally know and care about the individuals and all the standard critiques of communism are not applicable.