He was famous for his work on displacement activities (Dutch: overspronggedraging)  and the hierarchy of instincts. Already in the thirties he realised the common characteristics between instincts in humans and other animals. In one of his experiments in Western Africa he exposed a stuffed panther with an electronic moving head to chimpanzees, who attacked it with sticks, thus illustrating to which extent early man could have kept wild animals at bay even before spears and other weapons were invented.
- Displacement Activities and Arousal
- Kortlandt, A. (1972) - New perspectives on ape and human evolution, Amsterdam, Stichting voor Psychobiologie.
Kleindienst, M. R., Burton, F. D., & Kortlandt, A. (1975). On new perspectives on ape and human evolution. Current Anthropology, 16(4), 644-651. Link to article
- Dutch Wikipedia has more information about Kortlandt.