From the article: “The idea is pretty simple,” said Richard Wiener of the Research Corporation for Science Advancement, and the University of Arizona.
“It posits that social groups that have more members are going to be more attractive to join, and it posits that social groups have a social status or utility.”
In other words, people are like cattle and move with the herd. Or, in the case of Islam, they move in fear of the cattle-prod.