roadkill brings up an intresting point and while reading it a (gasp) thought hit me. Our world knows competition and evolution. What drives evolution? It is the competition? Allow me lay another possibility on you. What if the dominate driver is raditation? Either from the sun or from the various radioactive componets within our own planet? Need I mention the background level of raditation that is always present within our enviroment? If an alien system did not have these componets, would they advance through evolution? If they didn't, chances are good that their aggressive tendenacies would be much lower or possibilty higher if the raditation was higher. Higher levels of raditation would encourage more mutations over time, driving evolution at a faster pace.