R. A. Delgado Jr.
The Mind of the Chimpanzee: Ecological and Experimental Perspectivesby Elizabeth V. Lonsdorf
Understanding the chimpanzee mind is akin to opening a window onto human consciousness. Many of our complex cognitive processes have origins that can be seen in the way that chimpanzees think, learn, and behave. The Mind of the Chimpanzee brings together scores of prominent scientists from around the world to share the most recent research into what/i>… See more details below
Understanding the chimpanzee mind is akin to opening a window onto human consciousness. Many of our complex cognitive processes have origins that can be seen in the way that chimpanzees think, learn, and behave. The Mind of the Chimpanzee brings together scores of prominent scientists from around the world to share the most recent research into what goes on inside the mind of our closest living relative.
Intertwining a range of topics—including imitation, tool use, face recognition, culture, cooperation, and reconciliation—with critical commentaries on conservation and welfare, the collection aims to understand how chimpanzees learn, think, and feel, so that researchers can not only gain insight into the origins of human cognition, but also crystallize collective efforts to protect wild chimpanzee populations and ensure appropriate care in captive settings. With a breadth of material on cognition and culture from the lab and the field, The Mind of the Chimpanzee is a first-rate synthesis of contemporary studies of these fascinating mammals that will appeal to all those interested in animal minds and what we can learn from them.
Matthew V. Caruana
“[The Mind of the Chimpanzee] strikes a fine balance between naturalistic field studies and experimental approaches in captivity. . . . Highly recommended.”—Choice
“An ideal introduction for those interested in contemporary primatological research exploring the chimpanzee mind.”
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The Mind of the ChimpanzeeECOLOGICAL AND EXPERIMENTAL PERSPECTIVES
By Elizabeth V. Lonsdorf Stephen R. Ross Tetsuro Matsuzawa
The University of Chicago PressCopyright © 2010 The University of Chicago
All right reserved.
Chapter OneThe Chimpanzee Mind: Bridging Fieldwork and Laboratory Work
Ayumu is the five-year old son of chimpanzee Ai. Since his birth, he has observed his mother performing cognitive tasks using a computer touch screen. When he reached the age of four years, Ayumu learned to touch Arabic numerals in ascending order. Within six months he had mastered the ability to touch the nine numerals in the correct order as they appeared randomly arranged on the screen. We then proceeded to present Ayumu with a greater challenge: the masking task. In this task, after the first numeral on the touch-sensitive monitor is touched, all other numerals are replaced by white squares. The subject therefore must remember which numerals appeared in which location, and then touch them in ascending order. Ayumu's performance on this task was remarkable. He could remember the location of nine numerals, in the proper order, at a glance. Even after training for the same task, university students still could not match his performance. This is a case in which chimpanzees performed better than humans in a cognitive task.
The human mind is an evolutionary product, just like the human body. It is located in a soft tissue, the brain, which cannot fossilize like teeth and bones. Therefore, the fossil record of our evolutionary neighbors, such as Neanderthals (Homo neanderthalensis), does not reveal anything about how their minds worked. However, a comparison between the human mind and the mind of our closest living relative, the chimpanzee, may help us better understand the similarities and differences in cognitive functions between the two species, the shared characteristics that were present in our common ancestor, and those derived through species differentiation. Cognitive science has revealed various functions and capabilities of the human mind, but many unanswered questions remain regarding its evolutionary history. Therefore, an understanding of the chimpanzee mind can provide important insights into the evolutionary heritage of the mind of our own species.
Chimpanzees are remarkably similar to humans in many ways. The taxonomic group known as hominoids comprises humans and the great apes, which in turn include three genera: chimpanzees (including bonobos), gorillas, and orangutans. Recent advances in the study of the human and chimpanzee genome (Chimpanzee Sequencing and Analysis Consortium 2005) have revealed that chimpanzees are the closest evolutionary living relatives of humans. The difference in DNA between the two species is only 1.23%—so in other words, humans are 98.77% chimpanzee. This genetic difference is comparable to that between horses and zebras, estimated to be about 1.5% (Walner et al. 2003). You may think that zebras are horses with black and white stripes. If so, then you should also think that chimpanzees are humans with long black body hair.
Chimpanzee Life in the Natural Habitat
Chimpanzees live in the tropical rain forests and surrounding savannas of Africa. They probably once spanned most of equatorial Africa—including the land area of what are now at least 25 countries—and numbered more than a million just 100 years ago. Today, however, they are known to occur in only 22 countries, and an estimate by the World Conservation Union (IUCN) in 2003 put their numbers in Africa at between 172,700 and 299,700. This sudden decrease is linked to various human activities such as deforestation, poaching, and the bushmeat trade, as well as disease transmission (see chapter 28).
The common chimpanzee is usually classified into four subspecies (Fisher et al., 2004; Gonder et al. 1997): the eastern subspecies (Pan troglodytes schweinfurthii), the central subspecies (Pan troglodytes troglodytes), the Nigerian subspecies (which has only one small population, Pan troglodytes vellurosus), and the western subspecies (Pan troglodytes verus). The eastern subspecies is relatively small, and usually appears to have a paler face. The western subspecies is relatively large, and the face looks masked because of characteristic black patches around the eyes. However, there are large differences in physical appearance among individuals, so that even experts cannot readily recognize the different subspecies. Thanks to genetic analysis from blood, hair, and feces, it is now possible to differentiate individuals at the subspecies level.
Chimpanzees also include another species, known as the bonobo (Pan paniscus). About 600,000 years ago there existed the common ancestor of two species of hominids, Homo sapiens and Homo neanderthalensis; the Neanderthal man subsequently survived until only 30,000 years ago. Similarly, there are now two Pan species living in Africa, although they do not overlap in their geographical range. Bonobos live only in the densely forested regions south of the Congo River, in the Democratic Republic of Congo (former Zaire), central Africa, where neither the common chimpanzee nor the gorilla occur (Kano 1999; Boesch and Hohmann 2002; Furuichi and Thompson 2007). Once you recognize bonobos, it is easy to discriminate them from common chimpanzees: bonobos are more slender, and their voices are more tonal and richer in frequency modulation. The two species shared a common ancestor a little less than a million years ago (Becquet et al. 2007) and are thus equally close to humans (figure 1.1).
There are currently several major chimpanzee research sites in Africa (see appendix). Long-term observations spanning three to four decades and sometimes more have taken place at Gombe (Goodall 1986) and Mahale (Nishida 1990) in Tanzania, Budongo (Reynolds, 2005) and Kibale (Wrangham et al. 1996) in Uganda, Tai (Boesch and Boesch-Achermann 2002) in Côte d'Ivoire, and Bossou (Sugiyama 2004) in Guinea. There are also some young but important research sites such as the Goualougo triangle in the Republic of Congo (see chapter 11), Ngogo in Uganda (see chapter 15), Kalinzu in Uganda (Hashimoto and Furuichi 2006), and Fongoli in Senegal (Pruetz and Bertolani 2007). All of their information on the ecology, life history, and social life of chimpanzees comes from the collective efforts of people who have dedicated their lives to understanding chimpanzees in their natural habitat.
Chimpanzees may live in primary forests, secondary forests, gallery forests, and even in savanna. Long-term records from Bossou (Sugiyama and Koman 1992) indicate that they consume about 200 plant species, a third of the species available in their habitat. These include various plant parts such as fruit, leaves, flowers, bark, stem, roots, gum, etc. Since chimpanzees are omnivorous, they also eat insects, eggs, birds, and mammals. However, their communities differ remarkably in feeding repertoire. For example, the chimpanzees at Tai, Mahale, Gombe and Ngogo oft en engage in hunting for meat (Boesch 2002; see also chapters 15 and 18) while Bossou chimpanzees seldom eat meat. Chimpanzees also exhibit various tool uses unique to each community (McGrew 1992; Whiten et al. 1999; see also chapters 10, 11, and 12). A behavioral assessment based on time sampling revealed that Bossou chimpanzees use tools for getting food during 16% of their feeding time (Yamakoshi 1999). This was much higher than expected, and it suggests that chimpanzees in some communities really need tools to survive.
Chimpanzees live in groups termed communities or unit groups. Each community consists of multiple males and females, numbering together about 20 to 100 individuals. There are infants (less than 4 years old), juveniles (4 to 7 years old), adolescents (8 to 11 years old), young adults (12 to 35 years old) and old adults (36 years or older). These age classes may slightly differ between the sexes and among communities.
Thompson et al. (2007) examined mortality and fertility patterns in six free-living chimpanzee populations. They compared age-specific fertility patterns calculated from 534 chimpanzee births with equivalent demographic data from two well-studied human foraging populations, the !Kung of Botswana (Howell 1979) and the Ache of Paraguay (Hill and Hurtado 1996). The longevity of chimpanzees was about 50 years (figure 1.2). Age-specific fertility formed an inverted U shape, characterized by lower birth rates at the beginning and end of the reproductive life span. Compared with humans, chimpanzees reproduced more broadly across their life cycle. Reproductive performance began to decline at a similar age in chimpanzees and humans (25-35 years old) and approached zero at approximately the same age (50 years old).
Figures 1.3 and 1.4 show the mortality and fertility patterns of captive chimpanzees compared to wild ones (Kurashima and Matsuzawa, forthcoming). The dataset was based on the record of chimpanzees in Japan: 286 males and 388 females for the mortality curve, and 360 chimpanzee births by 118 females for the fertility curve. The mortality curves of the wild and captive chimpanzees were parallel (figure 1.3), although the mortality rate is lower in captivity. Fertility in chimpanzees declines at a pace similar to the decline in survival probability, whereas in humans it nearly ceases at a time when mortality is still comparatively low. Thus, the post- reproductive period of the lifespan was almost absent in the wild chimpanzees, and less marked in the captive chimpanzees (Videan, et al. 2006), while marked in humans and known as "menopause." Therefore, during the course of human evolution, the role of grandmothers in the care of their grandchildren may have been an important selective pressure (Pavelka and Fedigan, 1991).
According to the fertility pattern, the inter-birth interval of chimpanzees is about five years (although this varies among field sites and among individuals). This means that a mother typically gives birth to a single infant on average once every five years. Chimpanzees have twins rarely in comparison to humans, who have twins in one per every 100 births. Weaning in chimpanzees occurs at about four years of age, which means a long period of dependence. After weaning, a mother resumes the menstrual cycle (about 35 days) until the next pregnancy occurs. Upon pregnancy the gestation period is about 230 days in chimpanzees, in contrast to about 270 days in humans. At birth a chimpanzee baby weighs a little less than 2 kg, while the human baby weighs about 3 kg (see the details in table 1.1 described later). During the first five years of life until a younger brother or sister is born, the chimpanzee infant is fully taken care of by his/her mother, with little to no paternal care.
Around the age of five, sex differences in behavior, including tool use, may appear in chimpanzees. Female juveniles have a tendency to spend more time with their mothers, taking care of younger siblings, and partaking in tool-use activities such as termite fishing (Lonsdorf et al., 2004). Male juveniles have a tendency to associate more with adult males; they oft en patrol at the periphery of the territory (see chapter 15), and also follow estrus females, who advertise their reproductive status by the presence of a large pink ano-genital swelling.
Chimpanzees typically exhibit male philopatry, whereby males remain in their native community while females tend to emigrate at puberty. Chimpanzee society is therefore more patrilineal—characterized by the presence of multiple male generations including grandfathers, fathers, sons, and so on—compared to matrilineal societies which are characterized by the presence of multiple female generations with the presence of grandmothers, mothers, daughters, and so on. Most mammalian societies are matrilineal with female philopatry. A female chimpanzee in estrus receives ample attention from males of most age classes, including juveniles, adolescents, and adult males.
The History of Understanding Chimpanzees
As detailed above, the study of chimpanzees helps us understand the evolutionary foundation of human nature. The pioneer of the study of wild chimpanzees was Jane Goodall, although at the same time there were also several attempts by other scientists including Adrian Kortlandt and Kinji Imanishi (figure 1.5; Matsuzawa and McGrew 2008). This early fieldwork brought us much information on the life of chimpanzees in their natural habitat.
The pioneer of the study of the chimpanzee mind is Wolfgang Kohler (1925), known as one of the founders of Gestalt psychology. A Russian psychologist, Ladygina-Kohts (1935; 2002), also carried out groundbreaking work in comparing the development of chimpanzee infants with that of human infants. Other early attempts were focused on the rearing of chimpanzees by humans in a home setting, and on teaching spoken language to chimpanzees (Hayes 1951; Hayes and Hayes 1952; Kellogg and Kellogg 1933).
In parallel to the rise of fieldwork in Africa in the 1960s, there was a corresponding attempt to understand the chimpanzee mind in the laboratory. These were the ape-language studies in which researchers tried to teach American Sign Language to home-reared chimpanzees. In their pioneering work, Allen and Beatrix Gardner trained an infant chimpanzee named Washoe and claimed that she learned at least 132 kinds of ASL signs (Gardner and Gardner 1969). David Premack (1971) tried to teach a different system of artificial language, using colorful plastic chips, to a chimpanzee named Sarah. Duane Rumbaugh and his colleagues later used a lexigram system to teach Lana the chimpanzee (Rumbaugh 1977). Sue Savage-Rumbaugh aimed to teach both spoken language and its visual equivalents to Kanzi, a bonobo (Savage-Rumbaugh 1993). ASL was taught not only to chimpanzees (Fouts and Mills 1998) but also to lowland gorillas (Patterson 1978) and orangutans (Miles 1990). This paradigm of teaching human language to nonhuman animals has also been applied to non-primate species such as dolphins (Herman et al. 1984), dogs (Kaminski et al. 2004), and parrots (Pepperberg 1999). Criticism of these early studies came from Herbert Terrace, who taught ASL to an infant chimpanzee named Nim Chimpsky (Terrace 1979). He argued that the apes were not using the signs to communicate. After detailed analysis of video recordings of the ASL behavior, Terrace concluded that the results achieved by the Gardners could be explained by associative learning rather than by comprehension of the symbols' meaning.
Almost two decades later, we can now summarize the results of the ape-language studies that took place between the 1960s and the 1980s. It is clear that chimpanzees and other great apes can master language-like skills to some extent. However, there are clear constraints in their abilities to demonstrate the semantics, syntax, phonetics, and pragmatics central to human language (Matsuzawa 2009). Regarding semantics, chimpanzees can learn the use of symbols, such as ASL, plastic signs, or letters to represent objects, colors, numbers, and so on. However, their ability is limited in several ways. The number of signs or "words" learned was several hundred at most, and never exceeded 1,000. The rate of word acquisition did not increase but reached a plateau in the apes while it increases exponentially in humans. Regarding syntax, chimpanzees showed very little evidence for learning grammatical rules. They seldom used multiple signs in communicative contexts except for the simple repetition of signs within their repertoire. The mean length of "utterances" (MLU) was less than two words or signs, and even in the case of multiple sign use there was no clear evidence that syntactical rules were being followed. Regarding phonetics, it is apparent that no research succeeded in making the apes use their vocal tracts to produce various sounds with frequency modulation, even though humans and chimpanzees share the common developmental process of laryngeal descent (Nishimura et al. 2005). Regarding pragmatics, the language-like skills mastered by the apes faced the criticisms of Terrace and others. The apes oft en showed imitation of the human signers and replication of their signs. The paradigm of ape-language studies thus suffered two major problems: one was social cueing and the other was the removal of chimpanzee infants from their natural mothers, which is ethically unacceptable (see ethical note below).
Excerpted from The Mind of the Chimpanzee by Elizabeth V. Lonsdorf Stephen R. Ross Tetsuro Matsuzawa Copyright © 2010 by The University of Chicago. Excerpted by permission of The University of Chicago Press. All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
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