Are religious kids more selfish?

A scientific research discussed at Salon: Are kids from religious backgrounds really more selfish than their nonreligious peers?. Quote: Here’s the zinger: according to Decety and his colleagues, kids from more religious households are less altruistic, and more apt to deal out punishment, than kids from non-religious households. Corollary zinger: on the punishment front, Muslim kids are even more vindictive than Christians. The article is critical of this claim and comes with a whole series of arguments, such as the artificialness of the situation, the difficulty to define religiousness and the question whether you can generalize this experiment beyond its setting. I doubt those explanations. My guess would be that this has to do with group strength. People have only a certain amount of altruism. And when they are in a strong group they will spend more of that altruism inside the group and less outside. Religions bind people in strong groups. And that applies even more to minority religions like Islam and Judaism.