Brain, Behaviour and Evolution

David A. Oakley, H. C. Plotkin, David A. Oakley, H. C. Plotkin

• Publisher: Routledge
• Year: 2018
• ISBN:
  9781351370240
• Edition: 1
• Topic: Psicología
• Subtopic: Historia y teoría en psicología

Originally published in 1979, this book provides students with an example of the ways in which an evolutionary perspective can rephrase and clarify traditional questions and issues in psychology. The format provides the student firstly with the minimal amount of basic information in neuroanatomy, genetics and modern evolutionary theory in a form which is readily related to the remainder of the volume. The book then goes on to consider the relationships between different forms of explanation in biology, and the role of brain behaviour students in these relationships. Finally, the reader is given an opportunity to follow the reasoning which stems from a biological approach when applied to topics in human behaviour such as learning, dreaming, sleeping, exploration, anxiety, reasoning, intelligence and consciousness. Modern evolutionary biology places man in a broader context than does traditional psychology, and this new perspective reduces our tendency to view life solely from a human standpoint. The significance as well as the uniqueness of some traditionally 'human' attributes are challenged by this approach.

1 The evolution and genetics of behaviour¹

Linda Partridge

Introduction

Darwin’s theory of evolution through natural selection is the main unifying idea in biology today. In this respect the development of psychology has proceeded rather separately from that of biology. It has always concentrated upon man, and usually the comparative approach has not been used to study the evolution of behaviour, but in the hope that ‘animals’ will act as simplified types of human beings. Certainly there are some respects in which mechanisms basic to the organization of all behaviour can be best studied in animals. However, we lose a whole dimension of animal behaviour if we ignore its diverse origins and the selective forces which shaped it.

Animal behaviour is often known as comparative psychology in psychology departments, and as ethology in biology departments. Although they sometimes deal with similar subject matter, these two approaches have very different histories and aims. Comparative psychology takes place in the laboratory, and has traditionally been concerned with ‘intelligence’, problem-solving abilities and other mental traits in animals. Most of the studies have used the laboratory rat. These studies were based upon the idea of a phylogenetic scale of intelligence with ‘lowly’ animals at the bottom, man at the top, and rats and monkeys somewhere in between. One central assumption which has been made by comparative psychologists is that learning is the key to animal behaviour because most behaviour is acquired, and that because so little is built into animals, genetics and evolution are irrelevant to psychology.

Ethology, in contrast, is closely linked with genetics, evolution and ecology, and is the study of animal behaviour as an evolved character. In this approach both learned and inherited behaviour traits are studied in the context of the natural history of the animal. Rather than viewing the different behaviours and skills of different species as part of a phylogenetic scale of intelligence, ethologists consider that present-day species are evolved derivatives of ancestral forms which underwent diversification into many different species, which have become highly ecologically specialized. Every species has an aggregate of special abilities, each of which evolved as a response to ecological factors posing problems. Part of every animal’s repertoire is inherited, and for this reason the study of genetics is seen as highly relevant to animal behaviour.

These two approaches are much less separate than they used to be, and each has made useful contributions to the other. There is now little doubt that behaviour has evolved, and that both genetically determined differences between animals in how they behave, and differences in the context and extent of learning, can be understood in the light of ecological differences.

In this chapter an outline of current views on evolution and genetics will be given especially as they apply to behaviour including human behaviour. The application of evolutionary and genetic ideas to social behaviour will then be discussed.

The theory of evolution by natural selection

What follows is a brief outline of Darwin’s theory of natural selection. An excellent introduction to the subject is given by Maynard Smith (1975), and a more advanced account by Dobzhansky et al. (1977).

The clearest way to explain the theory is probably to give an account of the development of Darwin’s own ideas. When in 1831 he set off for his voyage on HMS Beagle, Darwin was already aware of many of the facts which eventually contributed to his theory. In the eighteenth century Linnaeus had introduced his classification of the known species of animals and plants. Linnaeus viewed species as fixed entities, members of the same species having a characteristic morphology which was different from that of other species. He grouped together species in a hierarchical classification, a process called taxonomy. His system is still used today. In it, for example, man is a member of the Family Hominidae (which includes fossil men as well as modern man), the Order Primates (which includes monkeys and apes), the Class Mammalia (which includes cows, hedgehogs, lions and dolphins), the Subphylum Vertebrata (which includes fish, frogs, reptiles, birds and mammals) and the Phylum Chordata (which includes all animals with a stiff rod or spine, the notochord, running along the length of the body). In his classification Linnaeus recognized that animals and plants fall naturally into groups resembling one another in a variety of respects. The whales, for example, could be classified as fish on the grounds that they live in water and are streamlined. However, unlike fish and in common with mammals they have warm blood, a four-chambered heart, a characteristic arrangement of the skeletal bones and other internal organs, and they suckle their young with mammary glands. The fact that species can be grouped on the basis of resemblance in many respects could imply either that species were created as variations on a number of themes, or instead that their similarities were caused by descent from common ancestors. Linnaeus himself believed in separate creation, and thought that he was uncovering the design of the creator in making his classification. In contrast, several biologists before Darwin held evolutionary views, believing that all living creatures are descended from one or a few ancestors, and that similar forms have a more recent common ancestor than those that have less in common. By implication such an evolutionary outlook would view species as changing entities.

Darwin was also aware that animals and plants are adapted to their environments. Animals which live in cold areas have special means of insulation, such as thick coats of fur or layers of fat below the skin. Some, such as the mountain hare, turn white in winter and are camouflaged against the snowy background. They turn brown again in spring at about the time the snow melts. Camouflage as a defence against predators is a common phenomenon in animals, examples of dramatic cases being the resemblance of some moths to dead leaves, and of other insects to twigs. Some harmless insects are similar in appearance and behaviour to poisonous forms or to species with stings and are hence protected against predation.

The occurrence of adaptation is particularly obvious both when members of distantly related species come to resemble one another because they live in similar environments (the similarity in form of whales and fish is an example), and when members of related species become different in form because of differences in habits. Moles and bats are both modern mammals derived from the insectivore stock. Moles burrow in the ground and their fore-limbs are modified to form powerful shovels, while the fore-limbs of bats are modified to form wings. Adaptation has been thought to imply design by a creator.

When Darwin visited South America he was particularly impressed by the fossilized animal remains which he found there. Many of them, for example the bones of the giant sloths and armadillos, belonged to species which had become extinct, but which closely resembled much smaller modern counterparts. Others, such as fossil horses, have died out altogether, since there were no horses in South America when the Spaniards arrived there in the sixteenth century. In his diary Darwin commented : ‘This wonderful resemblance between the dead and the living will, I do not doubt, hereafter throw much light on the appearance of organic beings on earth and their disappearance from it.’ He also speculated that the extinct species might have died out because of their failure to adjust to their environment. At about that time the geologists William Smith and Charles Lyell both showed that successions of fossils in rock strata gave evidence of continuous change of form through geological time.

Darwin’s views were crystallised by his visit to the Galapagos Islands, a group of volcanic islands in the Pacific some 600 miles west of Ecuador. He found that on several of the islands there existed giant tortoises, and that it was possible to tell from which island any particular tortoise came by the shape of its shell. This led Darwin to speculate that the different island forms, while still members of the same species, had diverged when geographically isolated from each other. Living on the islands Darwin also found a group of finches, now known as Darwin’s finches, consisting of fourteen very similar species. The finches are confined to the Galapagos, and they differ from each other in their bill shapes and feeding methods. Some have heavy bills and eat large seeds, others have more slender bills and eat smaller seeds, some eat insects and one feeds on nectar. There are few other land birds on the Galapagos, and the finches occupy between them a number of niches which on the mainland would be occupied by other birds such as thrushes, woodpeckers, warblers and so on. Darwin remarked: ‘Seeing this gradation and diversity of structure in one small, intimately related group of birds one might really fancy that from an original paucity of birds in this archipelago one species had been taken and modified for different ends.’ He speculated that the different species had diverged in a similar way to the giant tortoises while in isolation on different islands, and that when dispersal resulted in two divergent forms coming together on one island they had changed so much that they would not interbreed, and had in fact become two species.

When he returned to England Darwin encountered two further ideas which were important for his theory. The first of these was contained in Malthus’ ‘Essay on Population’, in which he argued, on the basis of human fecundity, that the human population is capable of increasing indefinitely in geometric progression. Since human populations do not increase in this way, Malthus argued, they must be held in check by the limited amount of food available. There is still little evidence that the main factor holding the human population in check was food, but the observation that animal and plant species are capable of indefinite increase in numbers under favourable conditions was important in Darwin’s theory.

Lastly, Darwin was impressed by the changes which could be brought about by selective breeding of domestic animals. Again, this suggested to him that species were not immutable and could be modified by selective breeding of particular varieties.

Darwin went on to argue that since animals do not increase indefinitely in numbers, it follows that not all individuals survive to sexual maturity, or that some sexually mature individuals do not breed, or that breeding individuals produce fewer offspring than they would under optimal circumstances. Not all individuals in a species are alike, and at least some differences between them will affect their chances of survival and their fertility. In the ensuing struggle for existence some individuals will be better adapted than others to survive and reproduce and these will leave more offspring. This process is called natural selection. If the characteristics which enabled their parents to survive and reproduce are transmitted to the offspring, there will be evolution of characters bringing about adaptation. Thus by the combined processes of natural selection and of inheritance, the adaptation of the population to its environment is continuously maintained or improved, or is adjusted to a changing environment. An important aspect of Darwin’s theory was that he believed that the hereditary variations upon which selection acted were in their origin non-adaptive. However at that time virtually nothing was known about the basis of heredity, and it was therefore doubted that such random non-adaptive hereditary variations could occur. This is discussed further in the next section.

Darwin’s theory was greeted with uproar for two reasons. First, it conflicted with the account of the creation of living things given in the Book of Genesis. Second, it implied that man himself was the result of natural selection acting upon random hereditary variations in ape-like ancestors.

Since Darwin’s death an enormous amount of work has been done in the fields of comparative anatomy, comparative embryology, population biology and genetics, and this work has yielded further support for the theory.

So far the evolution of the physical structure of animals has been discussed. Part of the structure of many animals is their nervous system, which is partly responsible for determining how they behave. There is now abundant evidence that behaviour can be adaptive in the same way as any other characteristic. One very elegant study of the adaptiveness of behaviour was carried out by Cullen (1957). She was studying a cliff-nesting seabird, the kittiwake, and found that in comparison with other species of gulls, which nest on flat ground, the kittiwake has certain behavioural peculiarities that adapt it to cliff nesting. Predation is less on cliffs than on flat ground, so that kittiwakes give fewer alarm calls and show less anti-predator behaviour such as the removal of conspicuous broken eggshells after the young have hatched. Parent kittiwakes do not recognize their chicks individually at least up to the age of four weeks, probably because the chicks cannot stray from the ledge. Ground-nesting gulls recognize their young a few days after hatching, and their chicks stray from the nest at an early age. Kittiwake nests are made of mud so that they stick to the rock ledges, while those of other gulls are made of grasses, mosses and other such materials. There are also differences in the aggressive and courtship displays, associated with the inability of young kittiwakes to leave the ledge in the face of aggression from strange adults, and with the cramped conditions on the ledges where courtship occurs.

There is also evidence that behaviour has evolved with other features in the formation of groups and species, so that it can be used as a character in taxonomy. Lorenz has used behaviour as a character in the taxonomy of ducks and geese. Any behaviour which is to be used as a taxonomic character must be present in all members of a species and it must be inherited. Lorenz has used various behaviours of young ducks and geese, and some of the aggressive and courtship displays of the adults as the basis of a classification. Behaviours which many species share are assumed to have evolved early in the formation of the group, while a behaviour which is present in only one species is assumed to have evolved after the separation of that species from the others. The use of behaviour resulted in several modifications to the classification of the ducks and geese.

It is rare to be able to see natural selection in action, but some examples have been produced by the activities of man. One example is the phenomenon of industrial melanism. One of the effects of industrial air pollution is to cause a darkening of tree trunks in the woods in industrial areas, both because soot is deposited and because gaseous pollution kills the pale lichens which grow on bark. Since the industrial revolution many species of moth which were previously pale in colour and were camouflaged on the tree bark have evolved dark colouration because of the spread of mutations causing dark colour. These dark moths are better camouflaged against the darkened bark than were the pale varieties and hence less likely to be eaten by birds. This change in colour has been accompanied by a change in the background selection by the moths. In the peppered moth a pale variety occurs in unpolluted rural areas while a dark form occurs in urban areas. If these two varieties are given a choice of white and black backgrounds on which to rest, the dark variety usually picks the black background, while the pale form usually selects the white background. Natural selection has here not only acted on mutations affecting the colour of the moths, but has also affected their background choice.

The extent to which learning occurs, and what can or cannot be learnt, is adaptive. Certain elements of behaviour seem not to be learned in that they appear in their usual form the first time a particular situation is encountered. A male fruitfly of a certain age will court the first female he encounters without having practised or observed othe...