http://www.nytimes.com/2006/07/25/health/25rats.html

According to the above article, some scientists have found that they can create aggressive or non-aggressive rats depending on which genes they flip. This might be some kind of contributor to something that I have thought about a lot: why European cultures are so bent on destruction and domination. Perhaps there is something to the aggressive gene.

It seems that basically all humans fight, though on vastly different levels. Some societies have/had no organized methods of warfare while others are completely organized around destruction on a massive scale. Perhaps the aggressive gene has been rampant in Europe for millennia, because it seems people and cultures of European descent lay waste on scale that no one else comes close to, and have been doing so for a very long time.