[Crossposted from New Books in History] Chimps, our closest relatives, kill each other. But chimps do not engage in anything close to mass slaughter of their own kind. Why is this? There are two possible explanations for the difference. The first is this: chimps are not programmed, so to say, to commit mass slaughter, while humans are so programmed. The second is this: chimps do not make their own history and therefore cannot make the conditions conducive to genocide, while humans do, can, and repeatedly have. In the former case, human genocidal behavior is part of our evolved "nature"; in the latter case, it is a historical artifact. After reading Ben Kiernan's sobering (Yale UP, 2007) I've come to believe that it is a bit of both. Much of what we know about the evolution of human psychology and the history of human genocide suggest that we have an ingrained, genetically-encoded, largely unalterable drive to want to kill one another in large numbers. That drive, however, seems to be triggered by particular historical circumstances, these being largely of our own making. In Blood and Soil: A World History of Genocide and Extermination from Sparta to Darfur (Yale UP, 2007), Ben explores the nature of these triggering circumstances by looking at the history of genocide over the past five or so centuries. He finds unmistakable commonalities among modern genocides, primarily in the world of ideology. When modern people begin to believe that there is something sacred about their "blood"–that is, their own kind–and "soil"–that is, the plowed fields that sustain their kind–they have taken the first step toward the creation of the above-mentioned triggering conditions. When they believe, further, that their "blood and soil" are threatened by another "kind," or they see an opportunity to extend the reach of their "blood and soil," the conditions are almost complete. All that remains is for elites in the community to mobilize the force necessary to launch a genocidal attack. At this point what was merely necessary for genocide becomes, with the addition of a will and a way, sufficient and our innate genocidal tendencies are enacted. The challenge, of course, is to avoid creating the conditions that foster "blood and soil" ideologies and set us on the road to ruin. Alas, thus far we have not been able to accomplish that important task.