ScienceWeek

ANIMAL BEHAVIOR: ON ADVANCED APE TECHNOLOGY

The following points are made by W.C. McGrew (Current Biology 2004 14:R1046):

1) The use of tools by animals to solve natural problems, especially in foraging, is well-known natural history [1]. The manufacture of tools, rather than merely using found objects, is far less common, being restricted to great apes and a few bird species [2]. Only chimpanzees and orangutans have tool-kits, that is, repertoires of different tool-types, that vary across populations [3-5]. Now comes the first report [6] of customary use of tool-sets -- two or more different types of tool used in sequence to achieve a single goal -- by a community of wild chimpanzees (Pan troglodytes) in the Congo Basin. The finding emerged from the innovative use of modern technology in field primatology: "spy-cams" to monitor shy apes in the jungle.

2) Non-human use of objects as tools is widespread: woodpecker finches prise out grubs with twigs, sea otters crack molluscs on stones, digger wasps tamp down burrow entrances with pebbles [1]. These animals, however, are "one-shot wonders", that is, each species is good at only one type of tool-use, and the objects are collected, used, and discarded on the spot, unaltered. Such simple acts require no inventiveness, being behavioral adaptations to fit certain task demands.

3) The fabrication of objects by transforming raw materials into instruments is a cognitive step forward, in that reshaping an item by reduction, combination, extension, and so on renders it more efficient [2]. Such elementary technology must be learned from others who are more proficient than the novice. Social learning probably underlies the making of palm leaf probes by New Caledonian crows, who use the resulting hooked instrument to extract insect larvae. Wild chimpanzees use twig, vine, bark, stem, or leaf-stalk probes to fish out ants, termites or honey from their arboreal or terrestrial cavities. Such flexible probes are clipped, peeled, stripped, split, etc. to the necessary specifications to do the job. Goodall first described this 40 years ago in the case of termite fishing by the chimpanzees of Gombe, Tanzania.

4) As long-term studies of wild chimpanzees proceeded, first in East Africa, then in West Africa, it became clear that populations of apes make and use a variety of tools, in foraging, social life, and body maintenance [2]. Moreover, each population has a different repertoire of elementary technology: some types are universal, such as bed-making; others are regional, such as nut-cracking in far West Africa [5]; and still others are unique to a single population, such as pestle-pounding at Bossou, Guinea. Systematic comparison across populations shows patterns that resemble those found cross-culturally when human societies are compared, for example, in that the present distribution of a custom reflects past diffusion from a likely single invention. Thus, a population's tool-kit is a technological profile of its material culture.

5) Further field studies revealed that chimpanzees spontaneously use tool-sets: a sequence of two or more tools needed to accomplish a single task. The first, anecdotal description was of an A-B-C-D sequence, in which a stout chisel-stick (A) was used to batter the entrance to a bees' nest containing honey. After this, a more pointed chisel-stick (B) weakened the barrier at a single point; then a bodkin-like stick (C) pierced the barrier; and finally a slender, flexible probe (D) dipped out the honey. Tool-sets are cognitively demanding, in that a correct ordering is required: thus, a dipstick is only useful once the honey reservoir has been made accessible by a bodkin. Late reports of tool-sets elsewhere emerged, but behavioral data were scarce, with most information coming (quasi-archaeologically) from the tools left behind [].

6) Sanz et al.[6] have now reported the use of two new tool-sets by chimpanzees in the Goualougo Triangle area of the Republic of Congo, in Central Africa. In this Congo Basin rainforest, wild chimpanzees tap termites from their earthen homes, using techniques that relate to the shape of the insects' mounds. For emergent, castle-like mounds, the apes perforate with a twig the mound's surface to re-open exit holes used by the termites. Having gained access, they use a slender probe to fish out the insects for food. This technique was known from scanty evidence, mostly of tools found at mounds, but Sanz et al.[6] have supplied the behavioral data to go with the artifacts.

References (abridged):

1. Beck, B.B. (1980). Animal Tool Behavior. (New York: Garland STPM Press)

2. McGrew, W.C. (1992). Chimpanzee Material Culture. Implications for Human Evolution. (Cambridge: Cambridge University Press)

3. Van Schaik, C.P., Ancrenaz, M., Borgen, G., Galdikas, B., Knott, C.D., Singleton, I., Suzuki, A., Utami, S.S. and Merrill, M. (2003). Orangutan cultures and the evolution of material culture. Science 299, 102-105

4. McGrew, W.C., Tutin, C.E.G. and Baldwin, P.J. (1979). Chimpanzees, tools, and termites: cross-cultural comparisons of Senegal, Tanzania, and Rio Muni. Man 14, 185-214

5. Boesch, C. and Boesch, H. (1990). Tool use and tool making in wild chimpanzees. Folia Primat. 54, 86-99

6. Sanz, C., Morgan, D. and Gulick, S. (2004). New insights into chimpanzees, tools, and termites from the Congo Basin. Am. Nat. 164, 562-581

Current Biology http://www.current-biology.com

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COGNITIVE SCIENCE: NUMBERS AND COUNTING IN A CHIMPANZEE

Notes by ScienceWeek:

In this context, let us define "animals" as all living multi-cellular creatures other than humans that are not plants. In recent decades it has become apparent that the cognitive skills of many animals, especially non-human primates, are greater than previously suspected. Part of the problem in research on cognition in animals has been the intrinsic difficulty in communicating with or testing animals, a difficulty that makes the outcome of a cognitive experiment heavily dependent on the ingenuity of the experimental approach.

Another problem is that when investigating the non-human primates, the animals whose cognitive skills are closest to that of humans, one cannot do experiments on large populations because such populations either do not exist or are prohibitively expensive to maintain. The result is that in the area of primate cognitive research reported experiments are often "anecdotal", i.e., experiments involving only a few or even a single animal subject.

But anecdotal evidence can often be of great significance and have startling implications: a report, even in a single animal, of important abstract abilities, numeric or conceptual, is worthy of attention, if only because it may destroy old myths and point to new directions in methodology. In 1985, T. Matsuzawa reported experiments with a female chimpanzee that had learned to use Arabic numerals to represent numbers of items. This animal (which is still alive and whose name is "Ai") can count from 0 to 9 items, which she demonstrates by touching the appropriate number on a touch-sensitive monitor. Ai can also order the numbers from 0 to 9 in sequence.

The following points are made by N. Kawai and T. Matsuzawa (Nature 2000 403:39):

1) The author report an investigation of Ai's memory span by testing her skill in numerical tasks. The authors point out that humans can easily memorize strings of codes such as phone numbers and postal codes if they consist of up to 7 items, but above this number of items, humans find memorization more difficult. This "magic number 7" effect, as it is known in human information processing, represents an apparent limit for the number of items that can be handled simultaneously by the human brain.

2) The authors report that the chimpanzee Ai can remember the correct sequence of any 5 numbers selected from the range 0 to 9.

3) The authors relate that in one testing session, after choosing the first correct number in a sequence (all other numbers still masked), "a fight broke out among a group of chimpanzees outside the room, accompanied by loud screaming. Ai abandoned her task and paid attention to the fight for about 20 seconds, after which she returned to the screen and completed the trial without error."

4) The authors conclude: "Ai's performance shows that chimpanzees can remember the sequence of at least 5 numbers, the same as (or even more than) preschool children. Our study and others demonstrate the rudimentary form of numerical competence in non-human primates."

Nature http://www.nature.com/nature

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EVOLUTION: ON THE MENTALITY OF CROWS

The following points are made by N.J. Emery and N.S. Clayton (Science 2004 306:1903):

1) Throughout folklore, the corvids (crows, jays, ravens, and jackdaws) have been credited with intelligence. Recent experiments investigating the cognitive abilities of corvids have begun to reveal that this reputation has a factual basis. These studies have found that some corvids are not only superior in intelligence to birds of other avian species (perhaps with the exception of some parrots), but also rival many nonhuman primates.

2) Traditionally, studies of complex cognition have focused on monkeys and apes [1]. However, there is no reason to assume that complex cognition is restricted only to the primates [2]. Indeed, the social intelligence hypothesis [3] states that intelligence evolved not to solve physical problems, but to process and use social information, such as who is allied with whom and who is related to whom, and to use this information for deception [4]. There is evidence that some other large-brained social animals, such as cetaceans, demonstrate similar levels of intelligence as primates [5]. Corvids also appear to meet many of the criteria for the use of social knowledge in their interactions with conspecifics.

3) The crow has a brain significantly larger than would be predicted for its body size, and it is relatively the same size as the chimpanzee brain. The relative size of the forebrain in corvids is significantly larger than in other birds (with the exception of some parrots) [2], particularly those areas thought to be analogous to the mammalian prefrontal cortex: the nidopallium and mesopallium. This enlargement of the "avian prefrontal cortex" may reflect an increase in primate-like intelligence in corvids.

4) To fully appreciate how corvid and ape psychology are similar, it is important to describe how corvids may represent their physical and social worlds, and how these forms of mental representation may be similar or dissimilar to those used by apes in solving similar problems. The authors use the term "understanding" to convey the idea that corvids and apes reason about a domain (physical or social) in a way that transcends basic associative and reinforcement processes.

5) Tool use is defined as "the use of an external object as a functional extension of mouth, beak, hand, or claw, in the attainment of an immediate goal". Although many birds, primates, and other animals use tools, it is not clear whether any of these species appreciate how tools work and the forces underlying their function. Perhaps the most convincing candidates are New Caledonian crows, who display extraordinary skills in making and using tools to acquire otherwise unobtainable foods. In the wild, they make two types of tools. Hook tools are crafted from twigs by trimming and sculpting until a functional hook has been fashioned and are used to poke out insect larvae from holes in trees using slow deliberate movements.

6) The crows also manufacture stepped-cut Pandanus leaves, which are used to probe for prey under leaf detritus, using a series of rapid back-and-forth movements or slow deliberate movements that spear the prey onto the sharpened end or the barbs of the leaf, if the prey is located in a hole. These tools are consistently made to a standardized pattern and are carried around on foraging expeditions. The manufacture of stepped tools appears to be lateralized at the population level and tool use at the individual level.

7) There are many aspects of corvid and ape cognition that appear to use the same cognitive tool kit: causal reasoning, flexibility, imagination, and prospection. The authors suggest that nonverbal complex cognition may be constructed through a combination of these cognitive tools. Although corvids and apes may share these cognitive tools, this convergent evolution of cognition has not been built on a convergent evolution of brains. Although the ape neocortex and corvid nidopallium are both significantly enlarged, their structures are very different, with the ape neocortex having a laminar arrangement and the avian pallium having a nuclear arrangement [2]. It is unclear what implications these structural differences have. However, cognition in corvids and apes must have evolved through a process of divergent brain evolution with convergent mental evolution. The authors suggest this conclusion has important implications for understanding the evolution of intelligence, given that it can evolve in the absence of a prefrontal cortex.

References (abridged):

1. M. Tomasello, J. Call, Primate Cognition (Oxford Univ. Press, New York, 1997)

2. N. J. Emery, N. S. Clayton, in Comparative Vertebrate Cognition: Are Primates Superior to Non-Primates? L. J. Rogers, G. Kaplan, Eds. (Kluwer Academic, New York, 2004), pp. 3-55

3. N. K. Humphrey, in Growing Points in Ethology, P. P. G. Bateson, R. A. Hinde, Eds. (Cambridge Univ. Press, Cambridge, 1976), pp. 303-317

4. R. W. Byrne, A. Whiten, Machiavellian Intelligence: Social Evolution in Monkeys, Apes and Humans (Clarendon Press, Oxford, 1988)

5. L. Marino, Brain Behav. Evol. 59, 21 (2002)

Science http://www.sciencemag.org

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