"The Lord commanded Israel to take arms against their brothers and chasten them before the LORD."
The result was more aggression from students that had known the obscure passage was from the bible, and more aggression from students that had been read the biblical call to arms. Both universities saw similar results, even among Vrije's non-believers.
Two questions came up immediately in my thoughts. First, why were non-believers swayed by the biblical sources? I can think of a couple of possibilities. To start with, who's to say that the students that were godless at the time of the study didn't grow up in a church environment? 'Atheist' doesn't mean you weren't indoctrinated into religion as a child.
The strength of a belief in something can carry even further than the belief itself. Here is a thought experiment: imagine the strictest teacher you've ever had, approaching you years after they ever had any real authority over you. They level their eyes at you and bark out your name in that familiar way. "We need to take a trip to the principle's office right now." Even though the phrase "principle's office" has no real meaning in your life now, your pulse might quicken anyway. I know mine would. It is a learned response to a specific stimulus, reappearing like an immune response to a long-absent disease.
In the same way, a response to biblical authority -- if you have ever had it -- can recur even if you no longer believe it has a divine authority.
But there is also the social impact that religion has on everybody, even atheists. As an atheist, can you really say that when you walk into a church, it feels like any other building you've ever been in? No, it feels different. There are strong associations that society, as a whole, grants to these buildings. Maybe if atheists and theists were on slightly more even ground, that might not be the case. But in the US, at least, theists outnumber us greatly. Their religion has an effect on us similar to how rapids might effect a small midstream pebble. The pebble is very different from the larger rocks in the river, but the same water that is tossed and turned by the larger rocks can toss and turn the pebble.
One obvious analogy to this is how atheists are being oppressed with dollar bills and pledges that hold reverent a god that we do not accept. We're caught in the currents of religion. This happens on emotional levels too. One of the bigger problems facing atheism today is the fact that we atheists are too accepting of our fate. Why did it take us 50 years to take the religious pledge of allegiance to the Supreme Court? We spent so much time just going with the flow that we now look like we're "on the offensive" simply because we finally decided we were tired of being drug along by the populist current.
The second interesting question that I had was a matter of causality. This study hasn't had time to be corroborated, so it's just one set of data. One study I remember hearing about in the 90s showed that couples that live together before marriage are more likely to get divorced. But does this mean that living together before marriage can lead to divorce, or that the people that tend towards divorce also tend towards living together before marriage. Or maybe there is a third element altogether, that is independently causing the first two?
This study might show that a belief in God can lead to more aggressive behavior. Or it might mean that aggressive people tend to be religious! There is no way of knowing without further study, and there are no guarantees even then. There is plenty of evidence of both in this world. The Old Testiment reads like a Rambo movie. And there are plenty of criminals that "find God" in prison. Maybe these concepts just naturally gravitate to each other.
Either way, I want to see more research about this. I would love to see this repeated with enough data sets that one could make a map of religion/aggression hot zones.