In 1913, the Anthropoid Station for psychological and physiological research in chimpanzees and other apes was founded by the Royal Prussian Academy of Sciences (Berlin) near La Orotava, Tenerife. Eugene Teuber, its first director, began his work at the Station with several studies of anthropoid apes’ natural behavior, particularly chimpanzee body language. In late 1913, the psychologist Wolfgang Köhler, the second and final director of the Station, arrived in Tenerife. During his stay in the Canary Islands, Köhler conducted a series of studies on intelligent behavior in chimpanzees that would become classics in the field of comparative psychology. Those experiments were at the core of his book Intelligenzprüfungen an Menschenaffen (The Mentality of Apes), published in 1921. This paper analyzes Köhler’s experiments and notions of intelligent behavior in chimpanzees, emphasizing his distinctly descriptive approach to these issues. It also makes an effort to elucidate some of the theoretical ideas underpinning Köhler’s work. The ultimate goal of this paper is to assess the historical significance of Köhler’s book within the context of the animal psychology of his time.

Psychological adaptation underlies all human behavior. Thus, sexual coercion by men could either arise from a rape-specific psychological adaptation or it could be a side-effect of a more general psychological adaptation not directly related to rape. Determining the specific environmental cues that men's brains have been designed by selection to process may help us decide which these rival explanations is correct. We examine six testable predictions against existing data: (1) Both coercive and noncoercive will be associated with high levels of sexual arousal and performance in men. (2) Achieving physical control of a sexually unwilling woman will be sexually arousing to men. (3) Young men will be more sexually coercive than older men. (4) Men of low socioeconomic status will likewise be more sexually coercive. (5) A man's motivation to use sexual coercion will be influenced by its effects on social image. (6) Even in long-term relationships men will be motivated to use coercion when their mates show a lack of interest in resistance to sex because these are interpreted as signs of sexual infidelity. Current data support all six predictions and are hence consistent with the rape-specific hypothesis, but this does not eliminate the side-effect hypothesis, which is likewise compatible with the findings, as well as with the further evidence that forced matings increased the fitness of ancestral males during human evolution. We suggest some research that may help decide between the two hypotheses.

Ethologists and others studying animal behavior in a “cognitive” spirit are in need of a descriptive language and method that are neither anachronistically bound by behaviorist scruples nor prematurely committed to particular “information-processing models.” Just such an interim descriptive method can be found in intentional system theory. The use of intentional system theory is illustrated with the case of the apparently communicative behavior of vervet monkeys. A way of using the theory to generate data - including usable, testable “anecdotal” data - is sketched. The underlying assumptions of this approach can be seen to ally it directly with “adaptationist” theorizing in evolutionary biology, which has recently come under attack from Stephen Gould and Richard Lewontin, who castigate it as the “Panglossian paradigm.” Their arguments, which are strongly analogous to B. F, Skinner's arguments against “mentalism,” point to certain pitfalls that attend the careless exercise of such “Panglossian” thinking (and rival varieties of thinking as well), but do not constitute a fundamental objection to either adaptationist theorizing or its cousin, intentional system theory.

Recent decades have seen a number of influential attacks on the comparative psychology of learning and intelligence. Two specific charges have been that the use of distantly related species has prevented us from making valid evolutionary inferences and that learning mechanisms are species-specific adaptations to ecological niches and hence not properly comparable between species. It is argued here that work using distantly related species may yield valuable insights into the structure of intelligence and that the question of whether or not learning mechanisms are niche-specific is one which can only be answered by comparative work in “nonnatural” situations. The problems involved in defining and assessing intelligence are discussed. Experimental work has not succeeded in demonstrating differences in intellect among nonhuman vertebrates. Hence the null hypothesis – that there are no differences in intellect among nonhuman vertebrates – should be adopted; the superiority of human intelligence stems from our possessing a species-specific language-acquisition device. One implication of the null hypothesis is that general problem-solving capacity is independent of niche-specific adaptations. A second implication is that problem-solving may involve relatively simple mechanisms; association formation in particular may play a central role in nonhuman intelligence, allowing the successful detection of causal links between events. Causality is a constraint common to all ecological niches.

In a dynamic world, mechanisms allowing prediction of future situations can provide a selective advantage. We suggest that memory systems differ in the degree of flexibility they offer for anticipatory behavior and put forward a corresponding taxonomy of prospection. The adaptive advantage of any memory system can only lie in what it contributes for future survival. The most flexible is episodic memory, which we suggest is part of a more general faculty of mental time travel that allows us not only to go back in time, but also to foresee, plan, and shape virtually any specific future event. We review comparative studies and find that, in spite of increased research in the area, there is as yet no convincing evidence for mental time travel in nonhuman animals. We submit that mental time travel is not an encapsulated cognitive system, but instead comprises several subsidiary mechanisms. A theater metaphor serves as an analogy for the kind of mechanisms required for effective mental time travel. We propose that future research should consider these mechanisms in addition to direct evidence of future-directed action. We maintain that the emergence of mental time travel in evolution was a crucial step towards our current success.

Working memory limits are best defined in terms of the complexity of the relations that can be processed in parallel. Complexity is defined as the number of related dimensions or sources of variation. A unary relation has one argument and one source of variation; its argument can be instantiated in only one way at a time. A binary relation has two arguments, two sources of variation, and two instantiations, and so on. Dimensionality is related to the number of chunks, because both attributes on dimensions and chunks are independent units of information of arbitrary size. Studies of working memory limits suggest that there is a soft limit corresponding to the parallel processing of one quaternary relation. More complex concepts are processed by “segmentation” or “conceptual chunking.” In segmentation, tasks are broken into components that do not exceed processing capacity and can be processed serially. In conceptual chunking, representations are “collapsed” to reduce their dimensionality and hence their processing load, but at the cost of making some relational information inaccessible. Neural net models of relational representations show that relations with more arguments have a higher computational cost that coincides with experimental findings on higher processing loads in humans. Relational complexity is related to processing load in reasoning and sentence comprehension and can distinguish between the capacities of higher species. The complexity of relations processed by children increases with age. Implications for neural net models and theories of cognition and cognitive development are discussed.