His early work also drew attention to deception and conflict resolution, nowadays two major areas of research. Initially, all of this was highly controversial. Thus, the label of "reconciliation", which De Waal introduced for reunions after fights, was questioned at first, but is now fully accepted with respect to animal behavior. Recently, De Waal's work has emphasized non-human animal empathy and even the origins of morality. His most widely cited paper, written with his former student Stephanie Preston, concerns the evolutionary origin and neuroscience of empathy, not just in primates, but in mammals in general.