MOTIVATION AND FITNESS

I trust that, after studying the material presented up to this point, the reader has a fair idea about the various factors underlying such motivated behavioural activities as mating, parental care, feeding, food selection, drinking, stimulus seeking and defensive or agonistic reactions. The material in the preceding chapters indicate that although the response patterns may differ, these motivated acts have one important feature in common. They are terminated when an end-point corresponding to a goal is achieved. The concept of fitness was discussed in the early part of this book with the presumption that organisms have evolved in such a way to maximise fitness. I discussed how evolutionary processes may have selected mechanisms that result in a particular behaviour. From this perspective, the functional significance of any aspect of behaviour is seen in terms of fitness maximisation or the chances it gives to the perpetuation of the organism's genes. The functional significance of mating behaviour is obvious, even though it may not directly enhance the survival of the individual. Although a motivated act such as feeding contributes directly to the survival chances of the individual, it does so through its contribution to the chances of gene perpetuation. The traditional distinction made between activities such as feeding, drinking or attacking and activities concerned with gene perpetuation such as sexual behaviour is unwarranted. All behaviour has been affected by evolutionary processes with consequences on fitness.

In discussing sexual selection, I presented material indicating that sexual dimorphism and sexual behaviour may decrease an individual's survival even though such attributes increase the chance of gene perpetuation.

Most of the literature in psychology and physiology that deals with feeding in animals and humans focuses on hunger or how much is eaten (the regulation of food intake) rather than what is eaten (the selection of foods). Motivation textbooks rarely elaborate on the determinants of food selection, and if they do, such discussions occur in the section on hunger. The fact that food habits are used in the naming of higher-level taxonomic groups (e.g. carnivores, herbivores or omnivores, etc.) supports the notion that food selection is a major force in evolution. The prominence of food selections in our daily life is also evident amongst humans. If animals and humans are to survive and reproduce in their environments, they must find and eat foods that provide all the nutrients necessary for self-maintenance and reproduction, as well as to avoid eating lethal amounts of toxic plants or animals that they encounter.

This chapter describes and discusses the mechanisms that explain how animals and humans manage to discriminate foods containing needed nutrients from ingestible sources that are either valueless or dangerous to eat. The other major issue concerns the tendency amongst humans to be selective in their acceptance of a small subset of many edible items that are available to them. Explanations of these two major issues will be accomplished by a discussion of built-in ‘hardware and software programmes’ cognitive or learning processes and socio-cultural factors (mainly in humans) which are responsible for the choice of foods.

I wrote this book as a text for intermediate and advanced level courses in motivation, and as supplementary material for courses on comparative psychology and biopsychology. Although there may be overlap with material in other current textbooks on motivation, the approach and treatment taken in this one is quite different. It does not present an exhaustive review of facts and anthology of theories in the field, but instead, attempts to cover selected material linked in a coherent fashion. In doing so I have attempted to make some sense of the diverse range of topics that are covered in other motivation texts. I have also attempted to indicate the interplay of material on animal and human research, and hope that the reader will find the presentation a natural one in which the transition between the two appears unforced.

The organisation of each of the substantive chapters begins with a consideration of ‘classic’ theories and studies of a specific motivated activity, and is followed by discussion of selected current developments indicating further complexities of the issue. Even though some earlier theories have been superseded by recent models, like Mook (1996), I believe that students will benefit from such exposure, and consequently, develop a better understanding of how current models and research evolved. Shortly after I had completed this book, I encountered others offering new insights that were not available during my preparation. Within the limited time remaining for the production of this book, I have attempted to fine-tune some of my presentation with some ideas that I have learned from these new works.

Until recently most psychologists studying reproductive behaviour focused on proximate causal mechanisms and paid scant attention to issues concerning the functional aspects of such behaviour. There are some outstanding exceptions. Although Donald Hebb is best remembered for his seminal work on physiological models of learning, memory and other cognitive processes, his views on evolution and behaviour also revealed foresight in the following statement. ‘The function of behavior in evolution is simply to keep an animal alive and well enough to mate and in other ways to get the next generation established, the process then repeating itself and leading to still another generation’ (Hebb, 1972, p. 171). Few psychologists during that era considered ultimate causal mechanisms in their theoretical analysis aside from short passing reference to the significance of evolutionary factors in the explanation of behaviour. They seldom ventured beyond that level. Textbooks on the psychology of motivation with an experimental emphasis tended to focus on proximate causal mechanisms underlying rat behaviour (Beck, 1978; 1990; Bindra, 1959; Bolles, 1967; Brown, 1961; Hall, 1961; Young, 1961).

Following the publication of E. O. Wilson's Sociobiology: the new synthesis (1975) and R. Dawkins' The selfish gene (1976), a new group of psychologists were inspired by the implications of evolutionary factors to the explanation of motivational processes. This ‘new generation’ of behavioural scientists which include Buss (1989, 1999), Cosmides & Tooby (1987; 1992; 1995), Daly & Wilson (1983; 1988; 1994) and Symons (1979) have reconceptualised motivational analysis through their incorporation of evolutionary theory.

Observations of animals placed into an unfamiliar environment indicate that they display a characteristic pattern of behaviour which suggests exploration. They typically move throughout the physical space and enter many parts of it. If unfamiliar objects are present in this environment, the animals may approach these objects and make physical contact with them. These actions are characteristic of stimulus seeking behaviour ‘which serves to acquaint the animal with the topography of the surroundings included in the range’ (Shillito, 1963). Such behaviour in which the animal familiarises itself with its environment may serve an adaptive role. By doing so, the animal acquires information that is potentially useful, such as discovering potential food sources and escape routes. The phenomenon is manifested in all mammals. The notion that familiarity of the environment assists solutions to problems encountered later is also relevant to humans using the World Wide Web. Users who surf the Web without any particular goal acquire information which may become useful to them in later contexts (Seltzer, 1998).

Russell (1983) suggested that there is more to be gained from immediate exploration of a new environment than from not exploring, and thus regards the former as an adaptive strategy. Not exploring would lay an animal open to the hazards of an unknown environment. In social animals such as the rat, exploration may also have the goal of establishing contact with conspecifics. This is often the case when the animal has been removed from a group for testing (Suarez & Gallup, 1985).

WHY THIS BOOK?

This book is concerned with the analysis of motivated behaviour from a biological perspective. Although some psychology students may find biological topics less to their personal tastes than material that is specifically human-oriented with a social emphasis, I hope that they may be pleasantly surprised by the material in this book. It is possible to link these topics and it has been attempted in a third year undergraduate Motivation course which I taught from such a perspective at the University of British Columbia, Canada, for over 30 years. The encouraging reactions of these students during lectures and in their course ratings has motivated me to share some of this material with you.

Texts by Colgan (1989) and Toates (1986) have focused on some issues in animal motivation which form the corpus of the present book, but these earlier books were relatively short and very selective in their coverage. Although this book adopts a conceptual framework similar to that developed in the Colgan and Toates books, it is less restrictive and thus appropriate for a broader based Motivation course. Most of the recent texts on motivation (e.g. Franken, 1994; Mook, 1996; Petri, 1996) are expansive, eclectic and almost encyclopaedic in their coverage of topics. Although the framework of this book is derived from the animal motivation tradition, it can also be used to analyse relevant issues in human motivation. Thus this work sits between the larger omnibus motivation texts and the smaller ones that focus specifically on animal motivation.

Almost every text devotes a chapter, or at least a section of one to the history of motivation, and then lists various definitions of this concept by different theorists.

Feeding is the means by which an organism acquires the materials for building, maintaining and moving the vehicle that carries the next generation. Since nutrition is the main requirement of all living systems, feeding preceded by food-seeking behaviour, is a necessity of life. Organisms must feed to live and they also must work to feed. Evolution has played a role in influencing the eating and drinking behaviour of all species. It has selected for the mechanisms that motivate the organism's ingestion of nutrients and its selection. There are two fundamental aspects of feeding: energy balance and diet selection. Energy balance deals with how much animals eat in relation to their energy expenditures, whilst diet selection deals with mechanisms that allow omnivores to choose the appropriate nutrients. This chapter will deal with the former and Chapter 5 will be concerned with the latter issue.

Organisms regulate their nutritional intake according to shortand long-term energy needs. The mechanism responsible for this regulation, which involves the maintenance of a constant, optimal, internal environment, is called homeostasis. This concept was introduced by Claude Bernard (1879) in his discussion of ‘le milieu intérieur’ and the necessity of the organism keeping its internal environment at a constant, optimal level. (For a detailed discussion of the key components of homeostatic mechanisms and their character of operation, see Schulze (1995).) An example that illustrates the concept of homeostasis is that of the thermostat. After it is set for a certain temperature, it reacts to deviations from that temperature (the set point) by changing the environment so that such deviations are eliminated.

ATTACHMENT ACTIVITIES

Motivational influences that are specifically social constitute the subject of this chapter. Social motives involve activities that affect interactions among organisms of the same species as well as organisms of other species. I will deal with only two issues in this short chapter: the formation and maintenance of social bonds between individuals; and that of pro-social and altruistic acts. The functional and proximate causal aspects of these phenomena will be considered in the analysis. The first and foremost social motive concerns the formation of the bond between an infant and its primary caretaker, usually the mother. The material in Chapter 3 deals with this issue from the perspective of the mother, whilst the material in this chapter complements it through an analysis of processes in the infant. The attachment of a human infant to its caretaker has biological roots. Both babies and adults are programmed by evolution to become attached in certain ways because the former is dependent upon the latter for survival. Attachment behaviours refer to a broad classification of behaviours that keep the infant in close proximity to an attachment figure. These behaviours include crying, clinging and approaching, as well as others produced when the infant is separated from the attachment figure.

Mammals live in a diverse array of habitats and social structures. The basic unit of the family is the mother and infant. However, our examination of material in Chapter 3 suggests that other conspecifics may be involved to some exent in infant caregiving. These caregivers can include the father, siblings or peers, or combinations of these conspecifics.

Drinking is the means by which an organism acquires fluids necessary for the normal functioning of the cells in the body. Water is the medium through which the chemical processes of the body operates. It is the largest component of the body and its volume must be defended within narrow limits. ‘The proportion of water to lean body mass (the body without fat) is essentially constant at 70%’ (Rolls & Rolls, 1982). The energy processes of the cell occur within a fluid medium. In Chapter 4, it was noted that feeding preceded by food-seeking behaviour, is a necessity of life. Similarly, drinking preceded by water-seeking behaviour is also a necessity of life. Living organisms are endowed with mechanisms that have been selected for, and which cause them to be motivated to seek and ingest water when their internal environment's water balance is disturbed. The animal's nervous system is supplied with information from a sample of body fluids, and drinking decisions are based upon the state of this sample. Just as the thermostat samples temperature at a site in a room, it is assumed that the drinking mechanisms sample the fluid environment at one or more sites.

Fluid regulation in living organisms represents a balance between intake and excretion of water. Each side of the equation consists of a ‘regulated’ and an ‘unregulated’ component. The regulated component represents factors which act specifically to maintain body fluid homeostasis (water balance). The primary factors that regulate water balance are thirst and pituitary secretion of the anti-diuretic hormone (ADH), which is also known as vasopressin (Verbalis, 1990).

When animals are exposed to aversive stimuli, particularly those of pain, they are likely to respond by either withdrawing from or attacking the source of the stimuli. ‘Pain is an anatomically developed sensory system genetically differentiated for survival and the defence of the body. Responses to painful stimuli either involve the skeletal musculature or are internal but they are experimentally quantified as escape and avoidance’ (Le Magnen, 1998, p. 4). Both types of responses to this source serve adaptive functions. In many species, specific escape mechanisms have evolved for dealing with physical danger. One of the simplest is the withdrawal reflex that removes the organism from damaging stimuli. When specific taste receptors are in contact with bitter substances, they result in a spitting reflex that protects the organism from ingesting possibly toxic substances that are generally associated with the bitter taste. In Chapter 5 the mechanisms by which rats learn to avoid smells and tastes that have previously been followed by illness were examined. Animals will also react to aversive stimuli with attack behaviour, particularly when escape is difficult. Such a reaction is particularly evident in feral animals.

TWO-FACTOR THEORY OF AVOIDANCE BEHAVIOUR

The standard situation or apparatus used to study responses to aversive stimuli is one in which a rat is placed in a shuttle box – a long narrow box divided in half by a partition. The floor of the box is a grid of steel rods that can can deliver a painful shock when activated by electricity. The rules of the experiment are as follows. The rat has a few seconds to cross the barrier over to the other side of the box.