Animal Intelligence

Cambridge University Press
9780521825047 - Animal Intelligence - From Individual to Social Cognition - by Zhanna Reznikova
Excerpt

Part 1

Development of ideas and methods in studying animal intelligence

‘Good day, Maestro Antonio,’ said Geppetto, ‘What are you doing on the floor?’

‘I am teaching the ants their ABCs.’

Carlo Collodi, Adventures of Pinocchio

Animal intelligence has been experimentally studied for not much longer than a century and controversial ideas about how animals learn and to what limits they understand still exist. This part is about dramatic adventures of ideas. This is not just a historical background which is usually considered by readers as a ‘second preface’ and the boring duty of the author to give due to predecessors and key players, before descending to particulars of modern discussible issues. This part also has no pretensions of being historically complete as a review. The reader can find historical analyses of the development of ideas and researches in animal behaviour, comparative psychology and comparative cognition in many books and journal reviews such as: Evans (1976), Griffin (1978, 1984), Macphail (1993), Dewsbury (1985), Kline (1989), Ristau (1991), Kimble et al. (1991, 1996, 1998), Balda et al. (1998), Slater (1999), Kimble and Wertheimer (2000), Shettleworth (2001) and Bekoff et al. (2002), as well as in other reviews which are cited in the relevant places. This part represents a biased author’s sample of ideas and methods in studying animal intelligence. Even from this brief review we will see that the rise of the scientific study of animal intelligence may be portrayed as progressive changes in experimental methods.

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Chapter 1

Evolution of views on animal intelligence

A tendency to study human and animal intelligence in parallel has been in evidence from the very beginning of regular observations and investigations. It was not an easy task to locate the seat of intelligence. The famous Greek physician Hippocrates (b. 460 BC) was the first thinker to prefer to avoid mystical interpretations of mental disease and to stick close to the empirical evidence. For example, in a treatise entitled ‘On the sacred disease’ (meaning epilepsy), he dismissed the usual demonic-possession theory and suggested that it was a hereditary disease of the brain. Hippocrites and also Plato recognised the significance of the brain. Later, around 280 BC, Erasistratus of Chios dissected the brain and differentiated the various parts.

Galen, a physician to Roman emperors and an early author of works on anatomy and physiology, who acquired great experience from practising for some time as physician to the gladiators, gave public lectures and anatomical demonstrations in Rome. In 177 AD he gave his famous lecture ‘On the brain’. Galen described the frontal lobes as being the seat of thought (and the soul). He expertly dissected and accurately observed many kinds of animals (mostly dogs, monkeys and pigs, because dissection of humans was forbidden) and applied, sometimes mistakenly, what he saw to the human body. In addition to giving a great deal of fairly decent, concrete advice, Galen theorised that all life is based on pneuma or spirit, and he believed that the brain generates and transmits special vital spirit through the hollow nerves to the muscles, allowing movement and sensation (for details see Young, 1970).

After the time of Galen, there was only very slow progress in the development of the concept of intelligence until René Descartes, the French mathematician, philosopher, and physiologist, proposed his model of the nervous system and thus established the first systematic account of the mind–body relationship. The first of Descartes’ works, De homine, was completed in Holland about 1633, on the eve of the condemnation of Galileo. When Descartes learned of Galileo’s fate at the hands of the Inquisition, he immediately suppressed his own treatise. As a result, the world’s first extended essay on physiological psychology was published only a long time after its author’s death.

Perhaps one of the earliest to write about animal behaviour in a modern scientific fashion was the British zoologist John Ray. In 1676 he published a scientific text on the study of ‘instinctive behaviour’ in birds. He was astonished by the fact that birds, removed from their nests when young, would still build species-typical nests when adult. He did not try to explain this, but noted the fact that very complex behaviour could develop without learning or practice. Almost 100 years later, the French naturalist Charles Georges Leroy published a book on intelligence and adaptations in animals. Leroy criticised those philosophers who spent their time indoors, thinking about the world, rather than observing animals in their natural environments. Only by doing this, he argued, would it be possible to fully appreciate the adaptive capacity and flexibility in the behaviour of animals.

The development of objective methods of analysis of animal behaviour is attributed to psychologists studying animal mind in the nineteenth century, based on ideas of evolutionism and Charles Darwin’s representation of the common processes that govern natural selection in humans and other species and the psychological continuity between humans and other animals.

The theory of evolution went back to the ideas of Buffon’s and Lamarck’s theory of evolution by means of the inheritance of acquired characteristics, and to the poem Zoonomia of Erasmus Darwin (1794–96) who elaborated similar ideas. Carl Linnaeus devised a system for classifying the diversity of known plants and animals, and Georges Buffon pursued a massive compilation of facts about animals, resulting in an encyclopaedia of 36 volumes. This stimulated energetic pursuit of discovery, an activity that continues up to the present time.

Evolutionism in the nineteenth century was primarily concerned with the interpretation of the geological, palaeontological and biological evidence. In the mid 1840s two crucial works – Charles Lyell’s Principles of Geology and Robert Chambers’s Vestiges of the Natural History of Creation – had become the Bible of many explorers and had instilled into naturalists an appreciation of how long-term change could be effected through the operation of slow, ongoing processes.

The evolutionism of Herbert Spencer was significant for the development of concepts of mind and brain. Spencer’s first serious intellectual endeavours were devoted to the study of phrenology, and it was from phrenology that he drew the conception of society as an organism in which interdependent, specialised structures serve diverse functions (see Young, 1970). To Spencer is certainly due the immense credit of having been the first to see in evolution an absolutely universal principle. Spencer’s theory of evolution actually preceded Charles Darwin’s, when he wrote The Development Hypothesis in 1852, which is an advocacy against creationism and in favour of a progressive (evolutionary) view. While in The Development Hypothesis, Spencer simply turned the creationists’ arguments against themselves, he also published ‘A theory of population, deduced from the general law of animal fertility’ in 1852. In this essay, an early formulation of the mechanism of natural selection can be found. Unlike Darwin, Spencer was never much of an observer, and his independent formulation of a theory of evolution developed from his speculations in social theory and psychology. His theory was not taken into serious consideration, largely because of a lack of an effective theoretical system for natural selection. Nevertheless, it was Spencer and not Darwin who first popularised the term ‘evolution’, and few people outside the field realise that the oft-used phrase ‘survival of the fittest’ was actually coined by Spencer. Although Spencer was wrong about the mechanism of evolution, modern views support his main theme: the adaptations of living things to their surroundings are evoked by problems posed by their environments.

Darwin published his theory of natural selection in On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life, often abbreviated to The Origin of Species, in 1859. This book revolutionised biology, and is one of the most revolutionary works ever published. Darwin had not read Spencer’s Principles of Psychology (1855) when he wrote this but added complimentary references into later editions. Darwin’s ideas were based on an enormous amount of natural observations. He had studied Lamarck’s theory of evolution when he was a medical student, but neither this nor his grandfather’s (Erasmus Darwin) theory had shaken his belief in the fixity of species by the time he became a professional naturalist in 1830 when he secured a position as ship’s naturalist aboard HMS Beagle. Upon returning to England, he published his observations in Zoology of the Voyage of the Beagle (1840). Darwin, reflecting on his observations, came up with a theory that had a non-Lamarckian basis for the variation that leads to adaptation.

Darwin assumed that organisms naturally vary in almost every attribute that they display, such as morphology, physiology and behaviour. Such variation is heritable; on average offspring tend to resemble their parents more than other individuals in the population. Organisms have a huge capacity for increase in numbers; they produce far more offspring than give rise to breeding individuals, but the number of individuals in a population tends to remain relatively constant over time. Thus there must be competition for scarce resources such as food, mates and places to live. Darwin called this a ‘struggle for existence’. As a result of this competition, some variants will leave more offspring than others. These offspring will inherit the characteristics of their parents and so evolutionary change will take place by natural selection. As a consequence of natural selection organisms will slowly acquire changes in traits, behavioural traits included, and become adapted to their environment. The blind force of natural selection drives the evolution of such changes. The key to Darwin’s argument is that there are heritable variations among individuals of a single species, and that such differences lead to heritable changes from generation to generation, which ultimately lead to the origin of an entirely new species from existing species.

Upon returning to England, Darwin began to develop his ideas on evolution in several ‘sketchbooks’ and developed the kernel of his theory, that of natural selection, by the year 1838. He held on to these ideas for nearly 20 years before publishing them, and only moved to publish because of the fear of being scooped. Alfred Russel Wallace, English naturalist, evolutionist, geographer, anthropologist and social critic, had sent Darwin a manuscript to read and was asking his advice on the content of the manuscript before he presented the ideas on natural selection to the scientific community; these ideas were very similar to Darwin’s own. By that time Wallace had travelled in the Amazon Basin and Malay Archipelago for about ten years and his collecting efforts had produced the astonishing total of 125 660 specimens, including more than a thousand species new to science. After publishing three books, Wallace in 1855 wrote and published the essay ‘On the law which has regulated the introduction of new species’ introducing the concept of evolution through natural selection basing on his observations on huge species diversity. In 1858, while on the island of Ternate, Wallace drafted his ideas on ‘the survival of the fittest’. He posted the letter by mail-boat from the island with the request that if Darwin thought the ideas worthy he should send the letter on to Charles Lyell. Through actions of his friends, the geologist Lyell and the botanist Joseph Dalton Hooker it was made possible for Darwin’s long efforts to be acknowledged jointly with those of Wallace. The paper that is made available here is the result of that forced union. Darwin published in 1858, communicating with Wallace on a joint paper to the Royal Society’s meeting in which they described the role of natural selection in evolution (Darwin and Wallace, 1858). Darwin (1859) then published his famous book On the Origin of Species.

Darwin’s On the Origin of Species contained a chapter devoted to an attempt to explain how instincts could evolve by natural selection. He considered this issue one of the most formidable objections to his theory. In another book, The Descent of Man and Selection in Relation to Sex (1871) Darwin introduced the idea that the difference in mind between humans and ‘higher’ animals, great as it is, certainly is one of a degree and not of a kind. His last book, published in 1872, The Expression of the Emotions in Man and Animals, was probably the first work on comparative ethology.

From the early 1870s experimental ethology (called psychology that time) had started to develop, and it was Douglas Spalding who initiated this, being a long way ahead of his time in experimental approaches. He was the first to study the phenomenon that we now call imprinting; he began the study of anti-predator reactions; he experimented with both visual and auditory releasers and set out the logic of comparing the behaviour of species born in different developmental stages. Perhaps Spalding would have been thought of as the founder of ethology if only he had lived longer.

Spalding published series of papers (one of them in Nature, 1872) in which the antecedent conditions of behaviour in young animals were systematically manipulated and variations in response observed. For example, he hatched chicks from eggs by using the heat from a steaming kettle, in order to examine the development of the visual and acoustic senses without the influence of a mother hen. In sum, he described a number of experiments on young chicks and ducklings, carefully observed for the first few hours after birth. His conclusions were that these young birds not only showed ‘intuitive’ powers of walking, scratching and pecking, but also possessed intuitive knowledge of various kinds. He asserted that they were afraid of bees and of the cry of a hawk, and that they intuitively knew the meaning of a hen’s call note and danger signal when heard for the first time. Spalding also kept young house martins in narrow cages thus depriving them of the possibility of flight and then, after maturation, compared them with control birds. It turned out that birds did not need practice to develop their vital behavioural patterns.

In his numerous experiments, Spalding tried to demonstrate the unwinding of a strategy of life as the development of an organism. ‘When, as by a miracle, the lovely butterfly bursts from the chrysalis full-winged and perfect’, he wrote in Macmillan’s Magazine in 1873 – ‘it has, for the most part, nothing to learn, because its little life flows from its organisation like melody from a music box.’

Although systematic and experimental, Spalding’s investigations were based merely on naturalistic observations. One of the first to introduce apparatus and quantification into the study of animal behaviour was John Lubbock. He was introduced to natural history particularly through the efforts of Charles Darwin, a friend of the family who came to visit the family’s home in County Down when Lubbock was only seven years old.

Lubbock published a dozen of books, several of which report his observations of animal behaviour. Among these, the book Ants, Bees, and Wasps: A Record of Observations on the Habits of the Social Hymenoptera, first published in 1882 and reprinted many times, is possibly the most remarkable. I would like to note that reading this book, in its Russian translation, was the event that influenced the author of this book, when a schoolgirl. Indeed, this book moved me from a decision to become a musician to take up entomology and ethology. I used to construct my first ant maze completely in Lubbock’s manner, with the use of small parts from my parent’s vacuum cleaner (it stopped working after that).

Lubbock’s book included a chapter entitled ‘General intelligence, and power of finding their way’. In this chapter Lubbock took a number of critical steps away from natural history towards the modern animal laboratory. His first innovation was to provide precise, detailed, quantitative descriptions of the conditions on an observation, not much different from those one would find in the methods section of a modern journal article. One of his innovations was to include actual data in the body of his text and to use these data to compute simple summary statistics.

For example, in observing ants learning to take an experimentally contrived route between food and the nest, Lubbock employed experimental techniques of importance for future research. Following his ants with a pencil as they pursued their way, Lubbock made and, in his text reproduced, detailed tracings of the ants’ paths. This is certainly one of the first attempts to make an analogue record of behaviour for later coding. To observe the progress made by his ants in learning to follow a new path from food to nest, Lubbock designed a number of simple pieces of apparatus that constrained the ants’ movements. These pieces of apparatus were, in effect, the first animal mazes.

Apart from being a powerful stimulus to the development of experimental investigations, Darwin’s ideas of succession in animal and human thinking gave new arguments for anthropomorphic and anecdotal approaches to animal behaviour. Basically, anthropomorphism, that is, attributing to animals the same qualities as humans, goes back to the Roman author Pliny the Elder, who considered, for example, the elephant as the nearest to humans in intelligence (and surpassing humans in chastity and prudence), to present-day examples (Cartwright, 2002). At the turn of the nineteenth century the conflict between the anthropomorphic and the objective study of psychology was reaching a boiling point.

For example, Romanes regarded animals as possessing the intelligence to solve a problem by reasoning. In his book Animal Intelligence (1881) he suggested the following criterion of mind in animals:

Does the organism learn to make new adjustments, or to modify old ones, in accordance with the results of its own individual experience? If it does so, the fact cannot be due merely to reflex action in the sense above described, for it is impossible that heredity can have provided in advance for innovations upon, or alterations of, its machinery during the lifetime of a particular individual.

This was quite a reasonable criterion but the claim was based on anecdotal evidences rather than on careful experimentation. After the publication in 1883 of Romanes’ book Mental Evolution in Animals, the use of the anecdotal method was seriously discredited and retrieval of manifestations of intelligence in animals met strong criticism.

One of the early lessons about the importance of controlled procedures stems from work that was done with a horse nicknamed ‘Clever Hans’. Hans’s owner von Osten devoted 14 years to the detailed education of this horse following to syllabus of a grammar school. He claimed that the horse could count and was capable of mental arithmetic operations such as subtraction, multiplication and division. Thorough examinations demonstrated that the trainer unwittingly gave the horse barely perceptible cues for the right answer (Pfungst, 1908). When Hans reached the correct number of hoof strikes the trainer’s expression changed slightly. The horse possessed such a great level of keenness of observation that he could catch sight of the pulsation of veins on his owner’s head. Hans responded to these cues and stopped striking his hoof. If deprived of the possibility of observing his trainer, Hans did not give the correct answer. Although these results were based on an honest delusion, it is worthwhile to note that von Osten first demonstrated the phenomenon which will later be called ‘autoshaping’ (see Chapter 6), and that he may be first to have suggested a variant of intermediate language (see Chapter 30) with which to develop a direct dialogue with animals.

I think it is appropriate to mention here that, in my observation, frequency of references to an anecdote about Clever Hans in scientific and educational texts correlates with the development of our knowledge about animal intelligence. Of course, fashion changes in science and another set of examples comes to take place of former ones. It would be interesting to note that there are no mentions of Clever Hans in fundamental textbooks on animal behaviour published in 1970s and 1980s (for example, Hinde, 1970; Dewsbury, 1978; Manning, 1979; McFarland, 1985) but the textbooks published during the last decade contain detailed descriptions of this story (Allen and Bekoff, 1997; Shettleworth, 1998; Pearce, 2000; Cook, 2001; Griffin, 2001). I have also noted that frequency of mentioning of the Clever Hans phenomenon in lectures and even in posters at International Ethological Conferences has increased from 1997 to the present.

To my mind, this is caused not only by fashion based on imitation as well as the authors’ wishes to underline their data verification, although these factors are at work, but also by attainment of a new level of knowledge concerning animal intelligence. As we will see further in this book, recent experimental studies show animals as doing more and cleverer things: they use artificial intermediary languages for direct dialogue with experimenters, demonstrate their abilities for rule extracting and representation, counting, using mirror images, creating cognitive maps, shaping cultural traditions and manipulating other creatures with Machiavellian tricks. There is a natural aspiration of modern investigators of animal intelligence to underline the fact that although experiments and observations have resulted in the discovery of amazingly clever behaviour in animals, they are completely differ from the Clever Hans phenomenon. Perhaps that is why another citation from those times – Lloyd Morgan’s law – is also found more frequently nowadays.

The predominance of anecdotal evidence of animal intelligence led one of the pioneers of comparative psychology, Lloyd Morgan, to suggest that no animal behaviour should be explained in terms of higher mental processes if it could be explained by simpler processes: ‘In no case may we interpret an action as the outcome of the exercise of a higher psychical faculty, if it can be interpreted as the outcome of the exercise of one which stands lower in the psychological scale’ (Morgan, 1900). This became known as Lloyd Morgan’s law, or the Law of Parsimony.

Being a successor of Romanes, Morgan drew heavily on Romanes’ work and was his literary executor. In 1896 Morgan published the important volume Habit and Instinct which included, among others, chapters such as ‘The relation of consciousness to instinctive behaviour’, ‘Intelligence and the acquisition of habits’, ‘Imitation’ and ‘The emotions in relation to instinct’. A large part of the book was based on Morgan’s own experiments and observations. Morgan repeated Spalding’s experiments on the early development of behaviour, with a considerable variety of species, and, while confirming many of his observations and conclusions, showed that some of them were erroneous. He decided that newly hatched chicks had no perception of the qualities of objects. They pick up stones as well as grain, bits of red worsted as well as worms, gaudy-coloured inedible caterpillars as well as those that are edible. They do not recognise water till they have felt it, and they do not know that water is drinkable till contact with the beak sets up the nervous and muscular reactions of drinking. By a series of careful experiments Morgan showed that young chicks have no fear of bees as bees, but merely fear them because they are large and unusual. They are equally suspicious of a large fly or beetle, and, though eating small worms greedily, are afraid of a large one. And when the chicks are a few days old, and are no longer afraid of large flies, they show no fear even of wasps, when presented with them for the first time. Experimenting with fear of predators, Morgan came to the conclusion that a similar principle of alarm develops in different species: any sight, or sound or smell very different from what they have been accustomed to alarms them, and they learn what is really dangerous either through the actions of their parents or by their own personal experience.

In fact, this statement was not entirely adequate, and the problem is still under discussion. But this was the first time that the problem of the development of complex behavioural patterns had been systematically attacked on the basis of experimental method. Since that time, this problem has been re-examined by many researchers. The first coherent theory of instinctive behaviour within the framework of ethology was developed in the early 1940s (see Chapter 2).

Morgan tried to divide innate from learned behaviour and thus to construct the idea of intelligence. Among other examples of learned behaviour, he described competitions for sheepdogs in the north of England, where dogs have to cope with rather complex tasks, such as driving sheep over a predetermined course, just obeying their masters’ six or eight whistle signals, often accompanied by gestures. The dogs behaved like Clever Hans demonstrating a remarkable ability to respond to their masters’ cues but in this situation the process was carefully watched. So, Morgan said, the intelligent animal is what he is trained to be – one whose natural powers are under the complete control of his master, with whom the whole plan of action lies.

This idea was corrected by Morgan’s own fox terrier Tony. Tony was not trained to lift the latch of the garden gate and thus to let himself out. The way in which the dog learnt the trick was on his own initiative. Tony naturally wanted to go out into the road, and after several attempts he raised the latch with the back of his head, and thus released the gate, which swung open. Once firmly established, the behaviour remained constant throughout the remainder of the dog’s life, some five or six years. And the famous psychologist could not succeed, notwithstanding much expenditure of biscuits, in teaching Tony to lift the latch more elegantly with his muzzle instead of the back of his head.

Morgan’s dog became the inspiration of infinite numbers of animals doomed to search for specific ways to open doors. It was Morgan’s influential lecture at Harvard in 1896 on habit and instinct that prompted Edward Lee Thorndike to elaborate his experimental approach based on the study of animals escaping from puzzle-boxes. Thorndike was experimenting with chicks, and when he moved to Columbia University in 1897, he took along his two best-educated chicks. At Columbia he expanded his sample, and in 1898 when he published his doctoral thesis, ‘Animal intelligence: an experimental study of the associative processes in animals’, he reported data on chicks, cats and dogs. So 1898 could be considered the year of birth of the puzzle-box method.

The introduction of the puzzle-box method into comparative psychology was the point at which objective experimental methods were introduced into psychology, and prepared the way for its absorption into behaviourism. This was to exert a profound influence on the study of animal intelligence. Like Morgan, Thorndike reacted against anthropomorphic representations of animal reasoning and began his experiments in order to discredit the anecdotal approach for describing the behaviour. Many observers of animals, he argued, have looked for animal intelligence, and never for animal stupidity.

Figuratively speaking, the objective study of intelligent behaviour from the earliest stages has been based on several ‘corner boxes’. First of all, there was Thorndike’s puzzle-box and, later, Skinner’s reinforcement box (the so-called ‘Skinner box’). Both were aimed at developing experimental methods for controlling and manipulating the presentation of stimuli, but in different ways. Being placed into the puzzle-box, an animal has to extricate itself, while in the Skinner box its only desire is to stay there as long as possible in order to get more and more rewards. Differing in their presentation of reinforcement, these two ways of studying animals’ capacity for solving problems resemble each other in principle: the animal is unaware of how the apparatus works. A combination of these two variants much later resulted in another kind of a box, a so-called ‘artificial fruit’. You are not placed into the box; instead, you are presented with a sort of a puzzle-box containing food, so the challenge is for you to extract a reward – but not yourself – from the box. The principle is the same: it is not necessary for a subject to understand machinery, just to find a way of opening the box by trial and error and then to repeat the found route again and again. The artificial fruit has been constructed mainly for studying animals’ abilities for imitation (see Chapter 25), and it is worth noting that the first attempts in this direction were based on Thorndike’s early experiments with chicks. The first variants of mazes that were applied for studying animal intelligence were also constructed within boxes. The American psychologist W. S. Small described his research which involved an apparatus for the study of intelligence and learning in rats that he had modelled on the sixteenth-century Hampton Court maze near London. While the specific design was taken from a diagram provided in the Encyclopedia Britannica, the suggestion for use of the Hampton Court maze was that of Edmund Sanford. Published in two parts in the American Journal of Psychology (Small, 1900, 1901) (‘An experimental study of the mental processes of the rat’), this paper prompted many investigators to use mazes for studying intelligence in animals. Besides acting with locked boxes (such as ‘artificial fruit’) and solving problems when they themselves were in boxes (e.g. puzzle-boxes and Skinner boxes), animals demonstrated their intelligence by placing one box on another. This came from an alternative Gestalt approach in which thought was seen as an organisational process by which a problem was reorganised or solved (see Chapter 17). Gestalt was not part of psychology’s mainstream in the first half of the twentieth century, in which behaviourism dominated. In the second half of the century cognitive psychology was to come together as a relatively coherent movement.

One of the first presentations of comparative and objective investigations of human and animal mental representation was by Leonard T. Hobhouse. In his book Mind in Evolution (1901), Hobhouse articulated a theory of intelligence defined in terms of levels of adaptive behaviour, introduced a series of animal problem-solving tasks that initiated the experimental study of complex animal behaviour, and reported evidence of sudden improvement in the learning curve that appeared to reflect animals’ ability to employ perceptual relations in problem-solving. Hobhouse referred to this as ‘practical judgement’, and later students in animal behaviour have termed it ‘insight’. Hobhouse described the development of adaptive ability of animals from the simplest tendencies to the maintenance of ‘organic equilibrium, through the relatively stereotyped, inherited, stimulus-specific reflexes and more variable but also inherited patterns of instinctive behaviour, to the individually acquired adaptations of intelligence’. According to his definition, intelligent behaviour was that ‘devised by the individual on the basis of its own experience for compassing the ultimate and proximate ends to which it is impelled’. The presence of intelligence was indicated by the modification of action in accordance with the results of experience, showing that in some degree the animal can correlate its own past experiences with its subsequent action. At the lower levels of intelligence, Hobhouse placed behaviour that is the result of habitually acquired correlations which function as general modes of reaction to circumstances. At the higher levels of intelligence, however, behaviour, was, in his view, purposive. Purposive action dealt with the complex and varying circumstances of individual cases; and, unlike habit, which was a general mode of reaction, higher intelligence was selective, choosing appropriate means from among a host of possible actions best suited to achieve the desired aims.

After outlining the broad trend of mental development, Hobhouse then turned to the general question of whether the higher levels of intelligence have been attained by animals other than humans. To address this question, he introduced an ingenious set of problems and described a long series of experiments employing these tasks with dogs, cats, monkeys, an elephant and an otter. The problems involved manipulations with a simple mechanism (e.g. pulling a string, pushing a door, pushing a lever, sliding a lid, lifting a catch) or even more complicated behaviour (e.g. box stacking or rake use with monkeys) to obtain food. In the animals’ response to these problems, Hobhouse found evidence of sudden improvement in the learning curve, improvement that he interpreted as the evidence that animals are, indeed, capable of some degree of higher intelligence.

Extending his analysis first to conceptual and then to systematic thought in humans, Hobhouse presented a four-stage theory of the development of intelligent adaptation from unconscious readjustment (Stage 1) through concrete experience and practical judgement (Stage 2), to conceptual thinking and will (Stage 3), and finally rational system (Stage 4) that anticipated certain of Jean Piaget’s ideas much later. Piaget also accepted ideas from of J. B. Watson and from J. M. Baldwin, with his classic study of infant behavioural development, ‘The origin of right-handedness’ (Baldwin, 1894). Thus a tendency to study human and animal intelligence hand in hand had been developed.

Among other great persons who rocked the cradle of experimental psychology were Wilhelm Wundt and William James. They established the first two laboratories in the world (in Leipzig and in Harvard, simultaneously in 1875) dedicated to experimental psychology and pioneered the concept of stating mental events in relation to objectively knowable and measurable stimuli and reactions. James used Spencer’s Principles of Psychology (1855) as the text for his first course in physiological psychology at Harvard (1876/7), although he was very critical of Spencer’s detailed formulations. Thorndike was one of the graduate students supervised by James and learned experimental psychology from his two-volume course The Principles of Psychology (James, 1890). At that time, students from all over the world journeyed to Leipzig to learn experimental technique and to return to their home institutions imbued with the spirit of scientific psychology.

Wundt considered mind to be an activity, not a substance. The basic mental activity was designated by Wundt as ‘apperception’. He discerned the process of excitations from stimulation of the sense organs, through sensory neurons to the lower and higher brain centres, and from these centres to the muscles. Parallel with this process run the events of mental life, known through introspection. Introspection became, for Wundt, the primary tool of experimental psychology. The method that Wundt developed was a sort of experimental introspection: the researcher was to carefully observe some simple events – ones that could be measured as to quality, intensity or duration – and record the responses to variations of those events.

In the next chapters we will consider the early development of two main approaches to the study of intelligence which have expanded in parallel from the beginning.

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