The Ultimate Guide To Raising Parrots

Unique Parrot Training Ebooks

Get Instant Access

A. afarensis H. habilis H. erectus H. sapiens

Ma = million years ago figure 9.3 A comparison of encephalization quotients, calculated as the ratio between brain and body sizes to the expected component of 0.67, a porpoise (c. 3.5), four species of dolphin (c. 4.0-4.5), and the increasing values in the hominid lineage from the australopithecines to modern humans. Note hominid EQ only pulls past that of the biggest-brained dolphins about 1.5 Ma ago. (Redrawn from fig. 3 of L. Marino (1996; citation is in note 92) with the permission of the author.)

range of the bigger whales far outstrips the great apes: a typical killer-whale weighs about seventeen times as much as a gorilla. Scaling of body and brain masses across these size differences is not necessarily easy. More importantly, the buoyancy of sea water means that a large body size can be achieved without the imposition of a crushing gravitational burden, and in addition a large part of the body tissue consists of blubber. As its primary function is that of insulation, it is neurologi-cally inert and accordingly requires no investment by the brain tissue. The net result is that toothed whales have a rather different ratio of body weight to brain mass when compared to the primates. Appropriate corrections therefore have to be made, but once this is done it can be shown that not only do several types of dolphin (including the Pacific white-sided, Tucuxi, common, and bottlenose) have large brains, but in proportion to the brains of our three nearest relatives (chimp, gorilla, and orang-utan) they are significantly larger.91 Indeed, as Lori Marino has shown, until about 1.5 Ma ago, these dolphins were the biggest-brained creatures on the planet. Only then, at about the time of Homo erectus, did the brain size of hominids overtake that of the dolphins (Fig. 9.3).92

The questions then arise as to how, when, and why did dolphin brains get so large, and to what extent are the convergences with the brains of the great apes actually informative?93 So far as the origins of the story are concerned, it is not surprising to learn that well-preserved fossil skulls of toothed whales are only moderately common. Nor has it been easy to measure the so-called endocranial volume, which is a fair guide to brain size, at least until the advent of non-invasive medical techniques, such as computer tomography (CT). In any event, the fairly limited evidence suggests that the early whales had brains of unremarkable size, some of which were, indeed below average.94 The transition by whale ancestors from a terrestrial habitat to an aquatic existence, the elucidation of which has been one of the triumphs of palaeontological investigation,95 was evidently not in itself a spur to bigger brains. A dramatic increase in brain size is apparent when present-day dolphins are compared with these early ancestors, but the exact history is still not resolved. The increase probably started in the Oligocene, about 30 Ma ago, followed perhaps by a further jump in the Miocene. Nor, too, is it yet clear whether these spurts of encephal-ization were geologically sudden or more gradual.96 Nevertheless, it appears that by the Miocene (if not before) brain size had increased suddenly, especially in the ancestors of the porpoises and dolphins. It is surely significant that this vast organ, which metabolically is ruinously expensive,97 has been maintained for a protracted period, probably far in excess of that for hominids, and possibly for as long as 20 Ma.98 Evidently big brains may be, in at least some circumstances, adaptively useful, and are not just fickle blips of happenstance that in due course sink back into the chaotic welter of the evolutionary crucible.99

What, however, might have initiated one or more upsurges in dolphin brain size? At present perhaps the best evidence is that the trigger was environmental, specifically the dramatic cooling of the Southern Ocean.100 Among the consequences of this event, which was the harbinger of global refrigeration that culminated in the present ice age, was increased oceanic productivity as marine upwelling intensified.101 As Australia pulled away from Antarctica, marking the final break-up of the once immense supercontinent known as Gondwana, so the circum-Antarctic current became firmly established, the ice caps began to spread down from the mountains of the Antarctic continent, and in the adjacent oceans the baleen-sievers and predatory toothed whales both diversified, the deep waters filling with their clicks, whistles, and other vocalizations. This environmental trigger has an interesting parallel, perhaps, with the hominid story because it has been suggested that the major increases in brain size in such forms as Homo erectus may have been encouraged by increasing aridity in Africa, imposing new stringencies but also spurring new possibilities.102

Large brains may therefore be favoured when the environment offers a special challenge. Their persistence for many millions of years requires, however, additional explanations. Of these it may be that the emergence of sophisticated social organizations (with an emotional dimension) and the necessary corollary of advanced vocalizations may be especially significant. The social structure of dolphin groups, especially in the well-studied bottlenoses, is directly relevant to the theme of evolutionary convergence.103 At first sight it might seem rather remarkable that the bottlenose dolphins show 'striking parallels in social organization and complexity with that of the chimpanzee',104 as well as parallels to the ateline or spider-monkeys,105 a group to which I return below on account of a series of other instructive convergences. Such associations fall into a category known as fission-fusion societies, which as the name suggests are rather fluid in their composition, with alliances and coalitions of varying durations.106 Societies of this type are, as Marino notes, 'extremely complex because they represent a constantly dynamic social situation involving the movement of different individuals into and out of groups at various times'.107 Even so, some individuals may stay together for protracted intervals, and a common feature is a stable alliance of two to three male dolphins. These males form temporary consortships with females. Mating is probably promiscuous, but so far as the females are concerned it is also highly coercive.108

The similarity with chimp societies is another fine example of convergence within social systems. Nor is this resemblance likely to be accidental. On the contrary, it is much more likely to be adaptive and arises because despite the radical ecological differences there is a deeper constraint imposed by the patchiness in space and time of food resources in both ocean and jungle.109 The parallels are not exact; why should they be? Moreover, as studies of the dolphins continue, so further complexities in the structure of their societies are emerging. They indicate that, in some ways, despite having a fission-fusion society, the dolphins have advanced further than our closest relatives, the chimps. It is now apparent that their societal structure is more complex than hitherto realized, and that with dolphin groups form so-called 'super-alliances'. This clearly implies that their intelligence is well suited to handling an extended social network comprising at least a hundred individuals.110 Such intelligence is also well attested in the examples of cooperation between dolphins and humans, notably in the dolphins' assistance with fishing by providing clues as to where to cast the net or in herding the fish.111

This example of convergence in a sophisticated social context finds another very interesting parallel, but this time between two larger-than-average mammals, the sperm whales and the elephants.112 Linda Weilgart and her colleagues comment that despite their self-evident differences in 'a remarkable number of ways, including life history and ranging behavior, sperm whales and elephants resemble each other more than they do other animals - even ones that share similar ancestries, diets, environments and predators. The closest resemblance is found in their complex and unusual, but comparable, social organization.'113 In both these gigantic mammals the females and young form highly social units, highly communicative with various long-distance vocalizations.114 Socialization is intense, and in the sperm whales, for example, there seems to be a form of 'babysitting' in which the vulnerable young are cared for by other adults when their mothers are engaged in deep dives in pursuit of food.115 The males, in contrast, are solitary and wide-ranging, and return to the mating game only when they are not merely sexually mature but big enough to win contests. Social complexity, communal care of the young, intelligence, and memory, as well as longevity, seem to be the key ingredients in driving this remarkable convergence.

In the sophisticated and dynamic milieu of many cetacean societies, it is not surprising that vocalizations are complex and varied, especially in the dolphins. As has been repeatedly pointed out, the relative opacity of water means that facial expressions are of very limited use, and so sound production and acoustics have largely taken priority. In the specific case of the dolphins their fission-fusion societies are probably highly dependent on the production of recognizable whistles and other noises.116 Indeed, there is evidence that the vocalizations are far from a cacophony. Dolphins are accomplished mimics, and the speed and accuracy with which they can imitate given sounds is highly impressive.117 Evidently they can make contact across quite substantial distances, and one group of researchers have identified what they term 'whistle matching', in which the receiving dolphin returns an effectively identical whistle to the sender.118 This, however, is a very controversial notion, and it is much more likely that the whistles are simply contact calls. In particular, Brenda McCowan and Diana Reiss119 present evidence that groups of about 12 dolphins have a shared whistle type, but embedded in this there are subtle variations that in part are individualistic. The extent to which individuals do or can recognize each other remains moot, but all would agree that dolphin whistles are by no means fully understood; interestingly the type of dolphin known as Cephalorhynchus does not produce whistles. Its vocalizations, however, are convergent on those of the phocoenid porpoises.120 It has been remarked that given their ability for mimicry and their frequent contact with humans it is rather surprising that dolphins' powers of imitation have not extended to our speech.121 As it happens, certain other marine mammals are not so restricted. A famous example concerns the captive Harbour seal, one Hoover. Perhaps because of a bout of illness, followed by attention-seeking, the seven-year-old Hoover started to mimic English words.122 As the investigators reported, 'One observer wrote in the files, "he says 'Hoover' in plain English." I have witnesses'.123 Perhaps because he lived in Maine, Hoover spoke with a Boston accent, although the tendency to slur words made him sound inebriated. A somewhat similar case concerned a beluga whale, who also repeated his name and evidently enjoyed socializing with humans.124 Lori Marino also tells me that in the New York aquarium the belugas imitate the sound of the elevated train that runs near by.

The failure of dolphins to imitate human speech should not, however, distract from more intriguing similarities. In their case what is especially significant is the way the infant dolphins learn to vocalize.125 As has been pointed out by various investigators, this process has strong parallels with humans: there is a whole range of sounds that evidently represent babbling, over-production, and finally an attrition to a more standard repertoire.126 Not only that, but notwithstanding the debate concerning 'signature whistles' (note 118), it is known that dolphin vocalizations are considerably more complex than was once thought.127 It is tantalizing to think that such vocalizations, and their parallels in birds (note 175, Chapter 8)

and some primates,128 might provide an analogy as to how humans learnt to speak. In this context it is also worth recalling some remarks by Marc Hauser and Peter Marler, who commented that 'no one would, of course, claim homology between [bird] subsong and [human] babbling.' Rather, similarities would be viewed as convergences, illustrating 'a basic set of strategies that any species would be likely to employ if it embarks on the development of a system of communication based on learned signals'.129 So, too, Diana Reiss remarks on the discovery of a 'surprising complexity and plasticity in the communication, orientation, and navigation systems of many species ... diverse species either use or can learn to use, to different degrees, symbolic or referential communication for intraspecific or interspecific exchanges. This suggests that there may be a convergence or continuity in the communication and cognitive abilities in animals from different evolutionary paths.'130 These comments on the commonalities of vocalization and thereby the transmission of information are potentially of universal significance, as it is now being realized that dolphins might provide a model of how to achieve communication with extraterrestrials. Nor need this be the only clue. Readers of Mary Doria Russell's The Sparrow will recall how the aliens were first detected in a transmission of their singing; so, too, the song of the humpback whales131 may be a contribution to a universal music.132

Nor should these comparisons in communication be taken as some sort of fanciful whimsy: it is possible to teach dolphins to understand sentences and take the appropriate action.133 The actual experiments involved two dolphins, each one of which was taught an artificial language based respectively on computer-generated sounds (approximating to, but sensibly enough not identical to, their whistles) and on signs given by the hand and arm movements of a human. What emerged was a degree of comprehension that not only associated 'words' as symbols for given objects, e.g. a ball or hoop, but mastered both syntax (word order) and semantics (meaning), even when the 'words' were presented in a novel order. Such instructions provided a short cut to learning new tasks, that otherwise would have involved laborious routines and training. Indeed, this work has been taken further and there is now good evidence that dolphins can understand human gestures that refer to different parts of their bodies.134 Thus a gestural symbol achieves, for the dolphin, a semantic meaning. It is difficult to avoid the conclusion that dolphins are capable of abstract thought via mental representations that entail symbolic referents.

Beyond humans such an ability is rare indeed, as Marino notes: 'The fact that artificial "language" studies can only be meaningfully attempted with these very few species [dolphins, bonobo chimps, and perhaps African Grey parrots] suggests that these few species have converged toward a level of cognitive complexity that allows them to understand a simple but symbolic and rule-based system of communication.'135 This is not to imply, incidentally, that in the specific case of dolphins, they may one day develop a language with grammar136, but their syntactical competence seems to be firmly established.137 Human language may, on this planet, be unique, but waiting in the wings of the theatre of consciousness are other minds stirring, poised on the threshold of articulation.

In this sense the wide divergences of opinion as to the extent to which animal communications are indicative of the origins of human language, let alone to the possession of sentience by non-human species, are less important than the realization that what we call language is an evolutionary inevitability. Most of the cognitive substratum is already firmly in place. Nor should we be fooled by the routine criticism that because only some primates, cetaceans, or parrots achieve syntactic competence then the rest somehow have failed. That competence may in fact be more widespread than we realize.138 But even if it is not, then the explanation for its evolutionary emergence is contextual, notably in terms of highly complex social worlds where communication and memory are adaptations to a constantly changing world.139 It would actually be more surprising if convergences did not occur in such complex contexts. Of course, the belief still persists that the emergence of human language was a contingent fluke, but everything else we know about evolutionary convergence and the exploration of functional 'spaces' makes this seem increasingly improbable. And what of grammar and syntax, how the world, as well as the word, achieves meaning? So far as humans are concerned, a universal grammar may have evolved as a result of natural selection that optimizes the exploration of 'language space' in terms of rule-based systems.140 These themes resonate, of course, with much of this book, that is, to address the question as to how life 'navigates' to particular functional solutions. This agenda has the potential, if not the promise, of revealing both a deeper structure to biological organizations and a predictability to the process.

Notwithstanding decades of interest, the more we learn about dolphins the more remarkable they seem to be. Not only are they intensely vocal, but they show other convergences. For example, their powers of memory, at least so far as lists are concerned, are strongly reminiscent of the memory processes seen in humans,141 and it seems likely that at least short-term memory is retained as internal representations.142 So, too, there are similarities in their response to uncertainty, the dither factor. Broadly speaking, when faced with a problem, humans decide either to avoid it (escape) or to collect more information. The difficulty is that in times of high uncertainty a decision to collect more information may lead to a catastrophic error. In comparing the uncertainty responses of humans and dolphins an investigation by David Smith and his colleagues concluded that 'The dolphin performed nearly identically ... Human and dolphin uncertain responses seem to be interesting cognitive analogs.'143

Another observation seems at first just a curiosity. Dolphins sleep, but they also need to swim continuously lest they drown by failing to come to the surface. What do they do? Effectively either the left or the right side of the brain falls asleep, while the other side remains fully conscious with the corresponding eye open. Interestingly, birds have convergently arrived at this arrangement.144 It seems possible that at least some birds can engage in such unihemispheric sleep while flying, but its principal function seems to be as a protection against attack. For dolphins, however, having only half a brain asleep is apparently to keep in contact with the rest of the school.145 Dolphin brains therefore show a high degree of what is referred to as inter-hemispheric independence. This is presumably a precondition for lat-erality, which is a well-known feature of the human brain, and may possibly occur also in the dolphins. As remarked above, dolphin brains (Fig. 9.4) are large, and the hominids outstripped them only about 1.5 Ma ago. So far as the degree of folding of the neocortex is concerned, it seems that in this respect the dolphin brain is the more convoluted.146 The same applies to the cerebellum, at least in the bottlenose and common dolphins, in which the cerebellum is significantly larger than in any primate, including humans.147 Marino and colleagues suggest that this enlargement of the cerebellum is not only linked to coordination of movement, but has broader functions

Less convoluted

Hemispheres not as independent No paralimbic lobe Slower auditory processing No echolocation

More convoluted More hemispheric independence Unique paralimbic lobe Faster auditory processing Echolocation figure 9.4 A comparison of the human (left) and dolphin (right) brains, with some of the principal differences listed. (From, courtesy of L. Marino, Emory University.)

connected with the complexities of sensory processing, memory, and cognition.

These differences, in neocortical folding and cerebellum, underscore a key fact. This is to the effect that the large brain of the dolphins may have arisen from a common mammalian substrate,148 but it is very far from being identical to that of the human.149 The contrasts include a marked and very different development of particular areas and lobes, with the temporal and parietal regions emphasized in dolphins as against the frontal and occipital in humans (and other primates). Particularly noticeable is the development in the dolphins (and other cetaceans) of a unique paralimbic lobe, unknown in other mammals, which evidently has a special role in a variety of functions, including vision, touch, and motor activities. As Marino notes, 'The segregation of the limbic and supralimbic regions by an interposed paralimbic lobe is a radical departure from the typical terrestrial mammalian pattern of cortical evolution;' she continues, 'The fundamental topography of cortical sensory projection regions in a cetacean brain also stands in stark contrast to that of the primates.'150 Nor are these the only differences: the neocortex is thinner, the internal laminae are less defined, and the cellular structure is generally simpler.151 To quote Marino again, 'The differences in gross morphology and topological arrangement of cortical sensory zones between cetacean and primate brains persist at an even deeper level in the form of profound differences in cortical cytoarchitecture.'152 Yet despite all these differences the degree of cognitive convergence is striking.

The presence of an enlarged cerebellum has already been alluded to, and it is probably no accident that it is similarly enlarged in the mi-crochiropteran bats, which also echolocate.153 We should also recall, at this juncture, the immense cerebellum of the mormyrid fish with their highly developed capacities for electrogeneration and electrore-ception (Chapter 7, p. 182). All these animals are masters of sensory processing, possessing in their different ways remarkable acuities. In the case of dolphins and humans it will be apparent that despite both are mammals their brains, as Lori Marino stresses, 'represent two fundamentally different cortical organizational themes ... [and thus] compels the conclusion that any similar complex cognitive processes between primates and cetaceans are convergent.'154 The evolution of the brain cannot therefore be divorced from its adaptational requirements and a corresponding moulding of function to those needs.155

figure 9.5 Dolphins with their bubble rings. (Photograph courtesy of Brenda McCowan, University of California, Davis and Lori Marino, Emory University.)

This is important, not only because it confers a predictability to the evolution of brain structure (see pp. 266-267), but because it also suggests that while the routes to adaptive success, of which one is a higher intelligence, may be quite strikingly different (as in dolphins and humans) the end-points converge again and again.

It remains the case that in some ways the dolphin brain is a curious amalgam of a rather archaic brain, reminiscent of the relatively primitive condition seen in such mammals as the hedgehog and the bat,156 combined with the massive enlargement of the deeply convoluted lobes that gives it an uncanny similarity to our own brains (Fig. 9.4). Even so, the complexity of the dolphins' social life, sophisticated and specific communication, and ability to mimic and learn clearly indicate that complex intelligence is not the unique preserve of humans, and that in some respects the convergence seen in dolphins is more compelling than the classical comparisons with the apes. To this list should, of course, be added the playfulness of dolphins, perhaps best exemplified by the blowing of bubble-rings (Fig. 9.5) where both some degree of forethought in their production and an ability to manipulate the ascending circle of air are again consistent with some degree of cognition.157 What is often regarded as a key ability, that of self-recognition (usually tested by using mirrors), has long been suspected in dolphins,158 and has now been unequivocally demonstrated.159

This finding is of particular importance because it helps to refute the notion that something like a human can emerge only by some quirky path of evolutionary happenstance. As the investigators, Diana Reiss and Lori Marino, remind us,

'Bottlenose dolphins, great apes, and humans all possess high degrees of encephalization and neocortical expansion ... Yet the brains of dolphins are markedly different from those of primates on many levels ... reflecting the fact that the cetacean ... and primate ancestral lines diverged at least 65-70 million years ago. The present findings imply that the emergence of self-recognition is not a byproduct of factors specific to great apes and humans but instead may be attributable to more general characteristics such as a high degree of encephalization and cognitive ability ... More generally, these results represent a striking case of cognitive convergence in the face of profound differences in neuroanatomical characteristics and evolutionary history.'160

The evidence therefore seems to be increasingly consistent not only with a cognitive capacity, but with one arrived at independently and convergently with humans. These abilities, it seems, can encompass a comprehension both of symmetry and of signs,161 thereby indicating that, as I have already suggested, the notion that dolphins might well be capable of abstract thought is not in itself intrinsically absurd.

In the wider context of the toothed whales (such as the killer whales) and other marine mammals (such as the elephant seals and the Weddell seals) it has long been recognized that their vocalizations are not necessarily uniform across their geographical ranges, but in some instances can be divided into recognizable variants, that is, dialects.162 Some investigators are now going further, and speak of the cultural transmission of behaviours (that is, a state in which transmission of information is no longer entirely reliant on the gene). And what is patently true of humans most probably applies also to various marine mammals, and perhaps not surprisingly to some birds.163 For various whales such transmission involves not only vocalization but other activities, such as feeding behaviours.164 In the light of such work it is difficult to escape two conclusions: first, that the emergence of cultural capabilities represents a continuum, and second that convergences are inevitable. This is not to deny that humans have gone further; they have what has been termed a 'hyperculture', but it does not rule out such a phenomenon evolving elsewhere, whether on Earth or on Threga IX. That cultural attributes are manifested in such features as vocalization should not make us forget that their contexts are ones that are firmly embedded in a social matrix. This in turn has intriguing ramifications, such as, for example, the convergent development of the female menopause. Far from it being a puzzle why evolution 'permits' post-reproductive females, there are in fact probably sound adaptive reasons why it should in some complex societies.165 More than an echo of this has also been found in the African elephants, where the oldest of the females also tends to be the wisest, the best able to remember elephants from other groups, and thus able to transmit the requisite social knowledge to her own 'family'.166 As already emphasized (note 112), elephant and sperm-whale social structures are strongly convergent,167 and it has been repeatedly pointed out that to slaughter the largest and oldest in such matrilineal clans is a stupid course of action if the result is to deprive the group of the accumulated knowledge that enables it to prosper. It is a small irony that as the Darwinian synthesis was emerging in mid-Victorian Britain the rooms were lit by the burning of sperm whale oil, and the soothing music from the piano arose as the fingers moved across the elephant ivory keys.168

In the case of whale vocalizations it is also evident that a number of discrete categories are recognizable, but in the context of their possible cultural transmission what is significant is that only certain call types change with time, whereas others remain invariant. As certain call types change in a particular social group (which has a matrilineal social structure; see note 165), they will typically diverge in structure from the sounds made by another social group, although it is also possible that on occasion calls will in fact come to resemble one another. In either case there is a clear implication that within a social group a component of this change must be by learning, that is, by a cultural instruction. In their study of a pod of killer whales and their vocalizations Patrick Miller and David Bain169 inclined to a view that the changes arose by cultural transmission mediated by learning, and they were not afraid to suggest that such learning might occur 'as a consequence of exposure to the sounds of tutors'. They concluded that the 'Vocal similarity [of the pod] seems to be correlated with the mul-tilayered structure of killer whale society, and ultimately to the social interactions that contribute to the stability of the social structure.'170 Shifts in sound production might certainly, as the various investigators are careful to point out, be underpinned by a genetic change, but it seems just as likely that it is by imitation, improvisation, and experimentation. So, too, in humpback whales the arrival of some 'foreigners' led to a rapid adoption of the new song, literally a 'cultural revolution'.171 And should we be so surprised? Like humans, these marine mammals are long-lived, show a high degree of cognition, demonstrate prolonged parental care, and form cohesive societies.

In their various ways a number of marine mammals, and especially the dolphins and some of the other toothed whales, are intriguing in their social complexity and cognitive abilities. Much is convergent with other intelligent mammals, including humans, and it is a clear enough indication that at least in this biosphere if we had not emerged as the cerebral species then at some point, and probably sooner rather than later, someone else would. In this sense, humans, as a biological property, were inherent from at least the Cambrian period, if not before. The life of a dolphin appears to be rich and complex, but in evolutionary terms these large-brained cetaceans seem to have reached an impasse. Because they are highly adapted for swimming and living in the sea, they would seem to be unlikely candidates for the emergence of an advanced technology. Even so, despite their aquatic milieu, when it comes to tool use then, once again, the flippered dolphins surprise us. At least one group, principally more solitary females, has learnt to root up conical sponges and stick them on to their anterior beak, a structure known as the rostrum.172 Several alternative explanations can be entertained. Perhaps it is just that dolphins enjoy fooling around. Another possibility is that the sponges have medicinal properties. The most likely explanation, however, is that the sponge acts as a natural glove and as the dolphin rootles around in the sea bed, so it receives some protection from an alarming array of venomous animals, such as the stone-fish, scorpion-fish, sting-rays, sea-snakes, and the occasional blue-ringed octopus. Nor is this the only example of tool use by cetaceans. We saw earlier evidence of cognitive capacities in the formation of bubble rings by dolphins, but the humpback whales produce nets and curtains of bubbles to trap their prey.173 Perhaps on planets that are entirely oceanic (see p. 92) all advanced cognition resides in cetacean-like societies. There, as Michael Denton reminds us,174 access to fire and the skills of smelting and metallurgy would for ever be denied.

grasping convergence

If the path to the humanoid is characterized by any feature other than the carrying of a large brain rich in mentalities, it is the tools dropped on the way. Chosen and then discarded, tools epitomize intelligence and the purposeful. To be sure, those constructed by animals may seem primitive in the extreme, but it is clear enough that human technologies ultimately are based on the same antecedents. More importantly it is also now obvious that such an evolutionary ability may be rare, but it has emerged independently a number of times: inherent in evolution is not only intelligence and cognitive sophistication, but also technology. Tool use, per se, is of course well documented in a wide variety of birds,175 but a particularly famous example is provided by the New Caledonian crows.176 This example has excited interest because of evidence for the manufacture of both particular tool types, including hooks,177 and their standardization, features that had been thought to be effectively restricted to the advanced primates. In addition, Gavin Hunt documents lateralization in tool use and a rule-based method of construction.178 He also stresses that in a number of respects the more famous chimpanzee tool cultures do not match that of these crows, and concludes:

At the least, crows provide an extant species for learning about the neuropsychology associated with ... tool-making, such as handedness, hook use and the shaping of tools to rule systems, including an opportunity to see whether left-hemisphere specialization of the brain for the organization of sequential, manipulatory behaviours in tool-making might indeed be phylogenetically very ancient. If crows' tool behaviour involves cultural transmission, they also offer the opportunity for studying tool-making by pre-modern humans where cognitive, behavioural and social processes may have resulted in largely repetitive rather than innovative tool manufacture, and symbolism and language were rudimentary or absent.179

Apart from the parrots, already mentioned, and for which considerable evidence for cognitive sophistication exists,180 many ornithologists have remarked on the general intelligence of crows. Recent observations on tool modification and goal-directed activities in the American crow bear this out.181

Tool use in chimps has, not surprisingly, received extensive attention. Most of the work focuses, reasonably enough, on the use of sticks and stones.182 The closely related bonobo is also known to engage in tool-making. Remarking on one particular case, Nicholas Toth and his colleagues183 noted that the bonobo in question, one Kanzi, showed 'exceptional progress to date [but] his skill in flaking stone still contrasts sharply to that of Oldowan hominids'.184 They were unsure as to whether this was more a reflection of manipulative abilities as against cognitive constraints. Interestingly, however, chimps also use twigs for dental care in activities that include cleaning the teeth and helping to yank out deciduous ones.185 Much of this activity is self-directed, but examples are also known of one individual performing elementary dentistry on another chimp.

Nor is tool use among non-human primates confined to chimps. Significantly in some of the New World monkeys, whose evolutionary history has been separated from that of the Old World monkeys (and their descendants, the great Apes) for about 30 Ma, have convergently acquired tools. In particular, capuchin monkeys (Cebus), and also some of the callitrichids (specifically the golden lion tamarins186) show extensive tool use for a variety of purposes, including a primitive lithic technology when provided with suitable materials in captivity.187 Suzanne Chevalier-Skolnikoff188 also emphasizes that tool use is unlikely to have arisen by trial and error (fiddling around if you will) but is a direct product of advanced sensorimotor abilities: that is, capability combined with motivation. It is difficult to escape the conclusion that once such abilities are in place, tool use becomes an inevitability. In reviewing the earlier literature on tool use by capuchins, Gregory Westergaard and Stephen Suomi provide an effective counterpoint to Chevalier-Skolnikoff's comments.189 They remark, 'We suggest that the ability to make and use simple stone tools is a primitive behavioral capacity that may have been "discovered" numerous times and utilized by more than one hominid genus and species'.190 This idea echoes an earlier suggestion by Sue Parker and

Kathleen Gibson of parallel developments in the capuchin monkeys and great apes.191 This theme was returned to by G. C. Westergaard and his colleagues192 in summarizing a discussion of handedness, locomotion, and tool use. They remark, 'We do not hold that parallels between capuchins, on the one hand, and apes and hominids, on the other, resulted from homologous processes. Instead, we speculate that an array of behavioral similarities, including food-sharing and tool-use, evolved through convergent processes in Cebus and the common ancestor of great apes and modern humans.'193 In parallel to the chimps, however, the capuchin tools do not rival the most primitive of hominid technologies, known as the Oldowan. Nor is it entirely clear why the capuchin seems relatively adept at tool use in captivity, but there are few reports of such activity in the wild.194 As Elisabetta Visalberghi195 notes, this may be due to lack of observation or to their tree habitat, whereas primate tool use is very much associated with ground activities.196 It is also worth remarking that in capuchin tool use the manipulation has a pronounced bias to right-hand employment.197 It is significant that this discussion is put in a selective context by the intriguing possibility of a separation in the brain 'between language and object manipulation'.198 In parenthesis, it is important to stress again that the point of this book is to explore the likelihood of the emergence of certain biological properties. It is not my intention to persuade you that capuchins will one day evolve into humans; they won't. To start with, their mentality has strengths, but also limitations.199 Nor need this tool use necessarily be an appropriate guide to early hominid activities.200 The simple point is rather that tool use is far from being some sort of quirky by-product of evolution, and when tools are first employed other things may become far more probable, at least in some circumstances.

The examples of the capuchin monkey and especially the New Caledonian crow demonstrate that tool use is patently convergent. For us tools and hands are almost synonymous, yet the birds (and even dolphins) are a reminder of valid alternatives. Yet, by and large, tool use would seem to be a prerogative of the vertebrates. So far as there are rivals in a terrestrial context, for advanced complexity we would most probably turn to the insects, some of whose marvels have already been explored. Consider, however, this account by Samuel Wendell Williston of the behaviour of a parasitic wasp.201 It is quite a long quotation, but if at the end you don't rub your eyes, obviously you are more immune to surprise than I am. Thus Williston writes:

An insect, alighting, ran about on the smooth, hard surface till it had found a suitable spot to begin its excavation, which [when finished] was ... nearly vertical, and carried to a depth of about four inches ... The earth, as removed, was formed into a rounded pellet and carefully carried to the neighboring grass and dropped ... When the excavation had been carried to the required depth, the wasp, after a survey of the premises, flying away, soon returned with a large pebble in its mandibles, which it carefully deposited within the opening; then, standing over the entrance upon her four posterior feet [so leaving the front two free], she ... rapidly and most amusingly scraped the dust with her two front feet, 'hand over hand,' back beneath her, till she had filled the hole above the stone to the top. The operation so far was remarkable enough, but the next procedure was more so. When she had heaped up the dirt to her satisfaction, she again flew away and immediately returned with a smaller pebble ... and then standing more nearly erect, with the front feet folded beneath her, she pressed down the dust all over and about the opening, smoothing off the surface, and accompanying the action with a peculiar rasping sound. After all this was done ... she laid aside the little pebble and flew away ... Soon, however, she comes back [with] ... the soft green larva [which] ... is laid upon the ground, a little to one side, when, going to the spot where she had industriously labored, by a few rapid strokes she throws out the dust and withdraws the stone cover, laying it aside. Next, the larva is dragged down the hole, where the wasp remains for a few minutes, afterwards returning and closing up the entrance precisely as before [an action that is repeated four or five times] ... The things that struck us as most remarkable was the unerring judgment in the selection of a pebble of precisely the right size to fit the entrance, and the use of the small pebble in smoothing down and packing the soil over the opening.202

Was this article helpful?

0 0

Post a comment