End of the Word for World is Forest

When reading the end of "The Word for World is Forest," I found the discussion between Lepennon and Selver very interesting.  Before leaving New Tahiti forever, Lepennon asks Selver if there has been more killing.  Selver answers that there has been no more killing between the Athsheans and the yumens.  However, Lepennon meant to ask if there was any killing among the Athsheans and Selver does not give a straightforward answer, but it is understood that they have killed among each other.  This made me wonder, if humans kill each other, was there some point in history where we did not kill one another?  Did some "god" come along, and introduce murder?  It is strange to think that once you are introduced to a new thing, there is no way to get rid of it and it will remain with you forever.  This idea can link to many wars in our history starting with the wars between Europeans and Native Americans, continuing to the Vietnam War, and the wars in the Middle East.  Once war was introduced, there was no way to escape.  War has become the way of solving our issues with greed and power and according to this novel, it may continue that way into the future.