To the Editors:

It is difficult for an author to respond to a review without sounding churlish, but at the same time, it is incumbent upon an author not to allow misrepresentations of his or her work to go unchallenged. It in is this spirit that I am moved to respond to Barbara Ehrenreich's review of my book Less Than Human: Why We Demean, Enslave, and Exterminate Others.

My mission in Less Than Human was twofold. First, I sought to demonstrate the extraordinary pervasiveness of dehumanization across cultures and throughout history as an incentive to violence against whole populations - populations that are imagined to be less than human. And second, I offered a theory of dehumanization: an account of what it is about human nature that makes dehumanization possible. It is in attempting to engage with this theory that Ehrenreich drops the ball. She puzzlingly characterizes my theory as claiming that human cruelty to other humans "is based on a kind of cognitive error - a failure to recognize our conspecifics." Errors are accidental, and therefore purposeless, disruptions of normal psychological processes. But I do not regard dehumanization as some sort of cognitive hiccup. Dehumanization has a function: the function of obliterating our awareness of the humanity of those upon whom we wish to visit harm. Ehrenreich goes on to assert in a similar vein that Smith passes over the fact that wars have also been fought routinely and repeatedly among people who do recognize each other as fully human - whatever that may mean - people who, in times of peace, intermarry and trade with each other, and who may be as difficult for an outsider to distinguish as Irish Protestants and Catholics, Serbs and Croats.

But I do not propose that warring groups must dehumanize one another; only that they are often inclined to do so. Our readiness, in times of war, to dehumanize those formerly regarded as fellow humans is not a counterexample to my thesis: rather, it instantiates the phenomenon for which my theory is intended as an explanation.

When we dehumanize others, two psychological dispositions work in tandem: our continued adherence - often in spite of ourselves - to the hoary notion that the cosmos is an ordered moral hierarchy of beings, and our tendency to distinguish the essence of a thing from itsappearance. We imagine that although certain others have a human appearance, they possess a sub-human essence. Although decked out in the superficial trappings of humanity, these beings are taken to really be dangerous predators, vermin, beasts of burden, or animals to be hunted for sport. The imaginative alchemy by means of which this transmutation is performed requires a mind that is endowed with considerable cognitive horsepower. Its perpetrator must be adept at juggling sophisticated concepts, such as essence and appearance, morally higher and morally lower. In other words, only creatures with minds like ours have what it takes to dehumanize - or, more broadly, "despeciate" - others.