Duane Rumbaugh was one of the first primatologists of the modern era (which began after WWII), to engage in comparative studies of the cognitive capacities of nonhuman primates.  In fact, it was Rumbaugh who drew the world's attention to the Order Primates and who helped initiate the International Primatological Society, IPS, the first academic society to be organized around an Order rather than a discipline. His work eventually led in two directions, first the development of the Transfer Index, a was completely new way of looking at learning. The TI seperated monkeys from apes as completely as did Gallup's mirror task.  From this arose the Primate Test Battery, a video based system to test cognitive skills across a wide range of tasks from memory to numerical skils in primates. The other direction was to look at language and its effect on cognition. Only Apes succeeded in the laguage tasks. With Lana's success arose a raft of critiques that - in the light of more recent findings about the structure of human language, are now rendered invalid. Rumbaugh's initial findings in all domains has remained sound. This includes fundamental differences between monkeys and apes in their capacity to spontaneously begin control their attention, to consciously monitor their own behavior, and then to alter it deliberately, or by their own choice. It is the ape's conscious capacity to control its attention and to conciously monitor outcomes in a cause/effect manner, that allows for the acquisition of langauge. This also allows for the creation of "personal self", as a being that exists apart from the current experience of the self. Language greatly assists the emergence of this ability in apes, as does early rearing in which the ape is carried but not seperated from its mother. This allows pointing and joint reference to appear far ahead of schedule and for the spontaneouls development of human  language in cross-species co-reared apes.  The presence of a wild-reared mother (not present in other captive environments)also allows for the emergence of a nonhuman form of vocal language. The implications of this work for future investigations of apes are discussed.