In 1975, De Waal began a six-year project on the world's largest captive colony of chimpanzees at the Arnhem Zoo. The study resulted in many scientific papers, and resulted in publication of his first book,
Chimpanzee Politics, in 1982.
In 1981, he moved to the United States for a position at the Wisconsin National Primate Research Center, and took his current position at Emory and the Yerkes National Primate Research Center in 1991.
His research into the innate capacity for empathy among primates has led De Waal to the conclusion that non-human great apes and humans are simply different types of apes, and that empathic and cooperative tendencies are continuous between these species. This is quite opposite to the view of some economists and anthropologists, but recent experiments on prosocial tendencies in apes and monkeys support de Waal's position.
His book
Our Inner Ape examines human behavior through the eyes of a primatologist, using the behavior of common chimpanzees and bonobos as metaphors for human psychology. He also writes a column for
Psychologie, a popular Dutch monthly magazine.
The contributions of de Waal to primatology started with
Chimpanzee Politics (1982), which offered the first description of primate behavior explicitly in terms of planned social strategies, thus introducing Machiavelli to primatology, leading to the label "Machiavellian Intelligence" that later became associated with it. In his writings, de Waal has never shied away from attributing emotions and intentions to his primates, and as such his work inspired the field of primate cognition that, three decades later, flourishes around themes of cooperation, altruism, and fairness. 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 animal empathy and even the origins of morality. His most widely cited scientific paper, written with his former student Stephanie Preston, concerns the evolutionary origin and neuroscience of empathy. De Waal's name is, of course, also associated with the Bonobo, the "make love - not war" primate that he has made popular. But even his Bonobo studies are secondary to the larger goal of understanding what binds primate societies together rather than how competition structures them, even though the latter is never ignored in his work (the original focus of de Waal's research, before he was well known, was aggressive behavior and social dominance). Whereas his science focuses on the behavior of nonhuman primates (mostly chimpanzees, bonobos, macaques, and capuchin monkeys), his popular books have given de Waal worldwide visibility by relating the insights he has gained from monkey and ape behavior to human society. De Waal strongly believes in mental continuity between humans and their fellow primates, as in the following quote from
The Age of Empathy:
“We start out postulating sharp boundaries, such as between humans and apes, or between apes and monkeys, but are in fact dealing with sand castles that lose much of their structure when the sea of knowledge washes over them. They turn into hills, leveled ever more, until we are back to where evolutionary theory always leads us: a gently sloping beach.”