The Thinking Ape

A Life-History Approach Towards Primate Cognitive Development

Anthropology 106: Primate Behavior and Ecology
A. Zihlman, Instructor
Copyright © 1997, 2000 B. Collie Collier
This is a final paper on Richard Byrne's book The Thinking Ape, tying it together with several of the readings and teachings of the Primate Behavior class. Not one of my better efforts, I'm afraid -- I was unfortunately somewhat uninspired.

The study of primate behavior has been heavily influenced in recent years by the 'life-history' approach. This paper will demonstrate the benefits derived from long-term studies which explore primate life-histories in order to clarify their behavior and cognitive development. Specific examples are Richard Byrne's The Thinking Ape: Evolutionary Origins of Intelligence and some of the class readings. Since these works are heavily based on research performed and information gathered within the life-history approach, and on hypotheses of the evolution of human intelligence drawn from comparative method grounded in this perspective, it is important to be clear on the concept.

The life-history approach is explained by Morbeck, Galloway, and Zihlman in their 1997 article. Life history, as applied to primate behavior and evolution, is based on whole organisms and whole lives. Long-term studies using both empirical observation and field experimentation examine and document the life stages, survival, and reproduction of individuals. The life stories of these individuals ("what the animal does in order to live and reproduce" Morbeck et al 1997) are emphasized. Evolutionary change in any population requires the prerequisite of individual variation; the compilation of these individual life histories produces a portrait of the population. The study of life histories requires a multi-generation, multilevel approach to adequately reflect the varying factors (e.g., injury, disease, psychosocial health, species-specific growth and reproductive timers, etc.) that influence both individuals and aggregated populations. In short, the studies adopt a holistic point of view towards long-term, objective observation of individuals within their social contexts.

In his book Byrne notes apparent intelligent behavior observed during long-term studies of modern primates. He then uses comparative method to extrapolate the possible evolutionary timing of the development of intelligence in the ancestors of modern-day humankind. As Schultz pointed out in 1933,

Since any phylogenetic change has to affect primarily the processes of growth, additional information on the developmental changes in monkeys and apes is one of the first requirements for a thorough appreciation of the peculiarities of human growth, which have separated man and the anthropoids.

Thus Byrne examines modern primate expression of a particular trait (in this case intelligence) through use of the life history approach, then logically deduces probable emergence of similar progressive stages of the same trait within our humanoid ancestors. He does this by noting fossil and DNA ancestral separations into new clades, then correlating early hominid intellectual development with the last known ancestor humans share with that clade. Thus if modern orangutans demonstrate a specific cognitive attribute (which will also be seen in humans), Byrne concludes this particular attribute must of necessity be common to the latest ancestor shared by both humans and all the great apes. This would date the evolutionary emergence of that attribute at 16 million years ago, since that is approximately when the fossil and DNA record indicates the ancestry of orangutans and humans diverged. Byrne makes these deductions through both application of data gathered from long-term studies of non-human primates and recent molecular studies of DNA.

Byrne's book is on the whole a thoughtful and clearly written exploration of intelligence in the animal world. He seeks out examples of what he refers to as "insightful" intelligence or cleverness; specifically examples of second-order, intentional deception or teaching. His definitional parameters for insight are stringently quantified and interpreted, perhaps more conservatively than would seem absolutely necessary. Byrne mentions possible occurrences of insightful intelligence (specifically intentional teaching) in African gray parrots and porpoises, as well as the great apes, who demonstrated both teaching and tactical deception. However, he also notes that since such behavioral tactics in the non-human animal world is investigated most carefully in the great apes, he will of necessity confine himself to close examination of those studies. His use of observational information gathered from long-term studies based on a life-history perspective and his conservative definition of insight as 'true' intelligence demonstrates his close adherence to careful and accurate scientific research.

Byrne's exploration of intentional deception as a possible indicator of insight is a good example of both his rigorous parameters in defining intelligence, and his research technique. While investigating this subject Byrne spoke to primate researchers engaged in long-term studies of free-ranging Old World monkeys and apes. He discovered most of the scientists had observed and carefully described in their notebooks cases of what appeared to be calculated deception. However, none of these cases were officially reported because each researcher had only one or two such examples; consequently they felt their peers would believe them to be anthropomorphizing the objects of their study. The general consensus was a belief that the animals could not truly be engaging in deliberate, insightful deception.

Since by that point the sheer number of cases had assumed statistical significance, and were being reported by skilled, respected primatologists, Byrne carefully examined all the relevant collected data from the pertinent long-term studies to determine if these were examples of true insight. His conclusion was that in the case of the Old World monkeys these were all cases of "priming." He extensively explains the difference between true cleverness and priming by excluding "stimulus enhancement and response facilitation to enhance associative learning (Byrne 1995)" from his definition of insightful intelligence. This narrows his exploration of insight to the great apes. Byrne spends the next several chapters exploring the definition of 'thinking,' the acquisition of language in the great apes as an example of insight, and possible evolutionary causes for the development of intelligence.

In the last few pages of his book, Byrne applies his research findings (by extrapolation) to the probable origins of insightful intelligence in early hominids. As a consequence the supposed main thrust of the book (the possible evolutionary development of intelligence in early hominids) appears almost as an afterthought tacked on in the last chapter, after coverage of the 'more interesting' subject of cognitive development and examples of insightful intelligence in the primates. True, as Byrne notes in the first chapters of the book, it is far too easy to extrapolate freely on the basis of very little information and come up with wild hypotheses that are revealed as nonsense in the next year or two of research. Further, as he also states, each additional year seems to reveal new and startling observations within the study of primate behavior that require reassessment of previously acquired data. Nevertheless, Byrne gives no hint of a possible continuum of early hominid behavioral possibilities, based on the results of his conclusions. He merely gives a succinct review of his previous chapters, then lists inferred ancestral cladic separation dates along with the associated category of continuing cognitive development. He speculates briefly on the possible precursors of language in primate cognition, and calls for more study in this area, then closes with a restatement of his belief in the chimpanzee as the most recent model of possible hominid development of intelligence.

Byrne's final chapter seems disappointingly anti-climactic in its dry adherence to only the most stringently quantified and conservative of known, observable facts concerning cognitive development in the great apes. However, upon reflection this is an excellent example of the life history approach as applied to primate studies. Specifically and individually, Byrne clearly states only what is observed, and then extrapolates upon it. Placing his book within the context of the multi-level, widely-spread, long-term investigation of primate intelligence increases the amount of careful individual research done within the scientific community. His hypothesis on the evolutionary origins of intelligence will either withstand the test of time, or be disproved by later analyses of further data collected from both ongoing and new long-term studies of primate behavior. Thus a multi-generational approach (both in animal observation and by the human observers) to primate behavior will reveal new insights into both primate and possible early hominid behavior.

The writing of articles on observed primate behavior has continued since the 1994 publication of Byrne's book, of course. On the whole, readings on the great apes currently still support various of Byrne's conclusions. Rumbaugh et al wrote in 1994 concerning the biobehavioral roots of language. In this study, second order teaching and cooperative observational learning (both elements of insightful intelligence according to Byrne) are shown by Kanzi, an 8 year old bonobo (Pan paniscus). Kanzi also conclusively demonstrates that in at least one individual bonobo, primate cognition does indeed contain the precursors of language acquisition, as Byrne speculated.

In 1996 deWaal's "Conflict as Negotiation" explored cooperative social behavior as transacted between individual chimpanzees. If we assume the great apes are (as Byrne hypothesizes) possible models for the development of intelligence in early hominids, then observed chimpanzee behavior that is roughly analogous (if perhaps more simplified) than modern humans might be expected. While we run the risk of anthropomorphizing, this expectation does indeed seem to be fulfilled according to deWaal. He mentions the ability of individuals to cooperate and compromise in order to accomplish a desired social goal, as well as observed, "'anecdotal'" evidence for "outraged" reactions in the chimpanzees involved in the study when their expectations of social cooperation are violated (deWaal 1996).

Also written in 1996 is Matsuzawa's "Chimpanzee Intelligence in Nature and in Captivity: Isomorphism of Symbol Use and Tool Use." His article concerns the captive chimpanzee Ai (who beneficially demonstrates the influence of individual personality on learning capabilities), as well as the free-ranging Bossou chimpanzee population. Matsuzawa discusses the preponderance of innovative behaviors on the part of females and juveniles and the transmission of learned cultural differences by traveling female chimpanzees (i.e., second order teaching). According to Byrne these characteristics are indicators of insightful intelligence. Matsuzawa's study thus gives a possible explanation for how evolutionarily selected cognitive development could be constantly improved and refined through succeding generations of early hominids.

The benefits of the long-term life-history approach in primate studies and upon the ensuing hypotheses can be clearly demonstrated not only by Byrne's book and later readings, but also by Zihlman's article "Reconstructions Reconsidered: Chimpanzee Models and Human Evolution." As noted above, in 1994 Byrne demonstrated (through observations related in his book) his belief in the chimpanzee as the most relevant recent primate model for early hominid cognitive development. Zihlman's article is a re-examination of both old and new data as it relates to use of the chimpanzee as a model for the evolution of early hominid behavior. As related in the article, the model was proposed as a hypothesis in 1976 by Tanner and Zihlman, based on observed anatomical and fossil evidence. In 1987 Tooby & DeVore put forth the baboon as a more behaviorally correct choice of model for early hominids, stating that the initial selection of chimpanzee was influenced by ideological preferences. In 1996 Zihlman reiterated her case for the use of the chimpanzee as a model by further refining the model. She presented new data (behavioral, molecular, and anatomical) which indicates the bonobo may be a more accurate behavior model for early hominids than the common chimpanzee (Pan troglodytes).

Zihlman's 1996 article was published after Byrne's book and contains information not then available to Byrne. However, Zihlman's conclusions both strongly support and further refine Byrne's hypothesis on the probable development of intelligence, by advancing the bonobo (one of the great apes that demonstrates insightful intelligence) as a model for early hominid behavior. Through examination of these texts we see observed data on individuals collected from long-term studies, which is then examined through the life history perspective and combined with empirical investigation. This approach enhances our understanding of both primate and possible early hominid behavior, by constantly increasing and expanding our knowledge.

Thus through review of Byrne's book and several associated readings we can make a good argument for the use of the life-history perspective in primate behavior studies. Good hypotheses arise from extrapolations on objective, explicit data concerning observed primate behaviors. Individual long term studies provide data on individual primates through generations; a multi-level approach within the field occurs when we compare studies with similar methodologies. Through time and continued long-term studies, new data on primate life histories will emerge, proving or disproving old hypotheses and allowing the continued accumulation and refinement of our knowledge of primate behavior.

Last Updated: Fri, April 21, 2000