ScienceWeek

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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COGNITIVE SCIENCE: ON ANIMAL COGNITION

The following points are made by James L. Gould (Current Biology 2004 14:R372):

1) When Rene Descartes (1596-1650) suggested that nonhuman animals are machines, he made formal a view widely taken for granted by most thinkers in the Western tradition. In the process, he conveniently supplied a rationale for the curious assumption that only humans have souls. (Swimming against the tide, Saint Jerome argued in the early 400s that certain animals might have small souls.)

2) In the 19th century, Darwin's theory of evolution by natural selection licensed a new take on the problem: the difference between human and animal mentality was more likely to be one of degree. His enthusiastic followers began to discover that other species are very clever indeed. G.J. Romanes (1848-1894), in his Animal Intelligence (1882) found thought in virtually every creature from insects to mammals, but was especially impressed with primates.

3) By 1900, the number of smart-animal stories reached flood stage. Theodore Roosevelt and the well-known writer John Burroughs took on what they called the Nature Fakers, who fudged the truth between fiction and fact. They mounted a blistering attack, for instance, on William Long's story of a woodcock that set its own broken leg using a cast made of mud. During the height of the debate came a gentle German schoolmaster and his famous pupil, Clever Hans. Hans, a Russian trotting horse, had learned the rudiments of addition and subtraction. He was known to read and spell, compute fractions and tell time, understand music and calculate dates. He tapped out most of his answers, but could also respond by pointing his nose.

4) Many notable experts observed Hans and questioned him with remarkable success, even in von Osten's absence. A panel formally appointed to investigate concluded that no trickery could be involved, but the members were quite reasonably worried that Hans was rather too clever. They engaged the psychologist Oskar Pfungst to study the horse further. Using a double-blind technique, Pfungst discovered that Hans was "reading" the tension in his audience: when he reached the correct number of taps, the observers unwittingly relaxed.

5) Perhaps the most even-handed thing that can be said about studies of animal cognition is that they have made animals look smarter and humans dumber than either group formerly appeared. Individual opinion differs on where to draw the line on thinking, but it seems clear that much of what we once took to be cognitive and largely human now appears to be widespread and at least partially innate. The power of automatic learning (in humans as well as animals) is much greater than we had thought, while evolution seems to have smoothed the path to abilities once considered intellectually impressive.(1-5)

References:

1. De Waal, F. (1982). Chimpanzee Politics. (London: Jonathan Cape), Gould, J.L. (1982). Ethology. (New York: Norton)

2. Gould, J.L. and Gould, C.G. (1999). The Animal Mind. (New York: W.H. Freeman)

3. Gould, J.G. and Marler, P. (1987). Learning by instinct. Sci. Am. 256, (1) 74-85

4. Griffin, D.R. (2001). Animal Minds: Beyond Cognition to Consciousness. (Chicago: University of Chicago)

5. In Animal Cognition in Nature. (1998). Pepperberg, I., Balda, R., and Kamil, E.C. eds. (San Diego: Academic Press)

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

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COGNITIVE SCIENCE: ON WORD-LEARNING IN DOGS

The following points are made by J. Kaminski et al (Science 2004 304:1682):

1) The rate at which most toddlers acquire their vocabulary is astounding: From about 2 years of age, typical English-speaking children incorporate about 10 new words per day into their vocabulary until they reach an average vocabulary size of 60,000 words by the time they graduate from high school (1). Several studies have shown that children have a set of operating principles that guide the task of word learning (2-4). However, it remains a matter of debate which of these principles are unique to language learning and which are more general cognitive abilities that may be shared with other living creatures.

2) The authors investigated the outer limits of a domestic dog's "word learning"; that is, his ability to acquire the relation between a word and the object that this word refers to (the referent). By studying his retrieval behavior with familiar and novel items, the authors specifically tested whether he would be able to infer the referent of a new word by exclusion learning: that is, to "fast map" (5) and retain this knowledge over time.

3) The study animal, Rico, is a border collie and was born in December 1994. He lives as a pet with his owners and was reported by them to know the labels of over 200 items, mostly children's toys and balls, which he correctly retrieved upon request. Rico was first introduced to fetching items when he was 10 months of age, when his owners placed three different items in different locations around the flat and asked the dog for one of these items. Rico was rewarded with food or play if he fetched the correct object. He was gradually familiarized with an increasing number of items. Typically, the owners introduced new items by presenting them and saying their name two or three times. Rico then got the chance to play with the new item, and it was subsequently integrated into the collection of other items.

4) The first experiment was designed to assess Rico's ability to correctly retrieve his various items under controlled conditions. The authors randomly assigned the 200 items he was reportedly familiar with to 20 sets of 10 different items each. While the owner waited with the dog in a separate room, the experimenter arranged a set of items in the experimental room and then joined the owner and the dog. Next, the experimenter instructed the owner to request the dog to bring two randomly chosen items (one after the other) from the adjacent room. While Rico searched for the requested item, he could not see the owner or the experimenter. He retrieved a total of 37 out of 40 items correctly. This first experiment demonstrated that Rico indeed knew the labels of these items.

5) In summary: During speech acquisition, children form quick and rough hypotheses about the meaning of a new word after only a single exposure -- a process dubbed "fast mapping". The authors provide evidence that a border collie, Rico, is able to fast map. Rico knew the labels of over 200 different items. He inferred the names of novel items by exclusion learning and correctly retrieved those items immediately as well as 4 weeks after the initial exposure. The authors suggest that fast mapping thus appears to be mediated by general learning and memory mechanisms also found in other animals and not by a language acquisition device that is special to humans.

References (abridged):

1. P. Bloom, How Children Learn the Meanings of Words (MIT Press, Cambridge, MA, 2000)

2. D. A. Baldwin, Dev. Psychol. 29, 832 (1993)

3. C. B. Mervis, J. Bertrand, Child Dev. 65, 1662 (1994)

4. M. Tomasello, Constructing a Language (Harvard Univ. Press, Cambridge, MA, 2003)

5. L. Markson, P. Bloom, Nature 385, 813 (1997)

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