The Bases of Human Behaviour

Behaviour understand the evolutionary nature of human behaviour, relate the functions of nervous system and endocrine system to behaviour, explain the role of genetic factors in determining behaviour, understand the role of culture in shaping human behaviour, describe the processes of enculturation, socialisation, and acculturation, and relate biological and socio-cultural factors in understanding human behaviour. After reading this chapter, you would be able to Introduction Evolutionary Perspective Biological and Cultural Roots Biological Basis of Behaviour Neurons Structure and Functions of Nervous System and Endocrine System and their Relationship with Behaviour and Experience The Nervous System The Endocrine System Heredity: Genes and Behaviour Cultural Basis : Socio-Cultural Shaping of Behaviour Concept of Culture Biological and Cultural Transmission (Box . ) Enculturation Socialisation Acculturation Key Terms Summary Review Questions Project Ideas Contents There are one hundred and ninety-three species of monkeys and apes. One-hundred and ninety-two of them are covered with hair.

The exception is the naked ape self-named, homo-sapiens. – Desmond Morris Evolution occurs through the process of natural selection. You know that members of each species vary greatly in their physical structure and behaviour. The traits or characteristics that are associated with high rate of survival and reproduction of those species are the most likely ones to be passed on to the next generations.

When repeated generation after generation, natural selection leads to the evolution of new species that are more effectively adapted to their particular environment. This is very similar to the selective breeding of horses or other animals these days. Breeders select the fittest and the fastest male and female horses from their stock, and promote them for selective breeding so that they can get the fittest horses. Fitness is the ability of an organism to survive and contribute its genes to the next generation.

Three important features of modern human beings differentiate them from their ancestors: (i) a bigger and developed brain with increased capacity for cognitive behaviours like perception, memory, reasoning, problem solving, and use of language for communication, (ii) ability to walk upright on E VOLUTIONARY P ERSPECTIVE You must have observed that people differ with respect to their physical and psychological characteristics. The uniqueness of individuals results from the interaction of their genetic endowments and environmental demands. In this world, there are millions of different species of organisms differing in a variety of ways. Biologists believe that these species were not always like this; they have evolved to their present form from their pre-existing forms.

It is estimated that the characteristics of modern human beings developed some , , years ago as a result of their continuous interaction with the environment. Evolution refers to gradual and orderly biological changes that result in a species from their pre-existing forms in response to the changing adaptational demands of their environment. Physiological as well as behavioural changes that occur due to the evolutionary process are so slow that they become visible after hundreds of generations. Human beings, the homo sapiens, are the most developed organisms among all creatures on this earth.

Their ability to walk upright, larger brain size relative to body weight, and the proportion of specialised brain tissues make them distinct from other species. These features have evolved through millions of years and have enabled them to engage in several complex behaviours. Scientists have attempted to study the relationship of complex human behaviour with the processes of the nervous system, particularly the brain. They have tried to discover the neural basis of thoughts, feelings, and actions.

By understanding the biological aspects of human beings, you will be able to appreciate how the brain, environment and behaviour interact to generate unique forms of behaviour. In this chapter, we begin with a general description of the nervous system in an evolutionary perspective. You will also study the structure and functions of the nervous system. You will learn about the endocrine system, and its influence on human behaviour.

Later in this chapter, you will also study the notion of culture and show its relevance to the understanding of behaviour. This will be followed by an analysis of the processes of enculturation, socialisation, and acculturation. Introduction two legs, and (iii) a free hand with a workable opposing thumb. These features have been with us for several thousand years.

Our behaviours are highly complex and more developed than those of other species because we have got a large and highly developed brain. Human brain development is evidenced by two facts. Firstly, the weight of the brain is about . per cent of the total body weight, and it is the highest among all species (in elephant it is .

per cent). Secondly, the human cerebrum is more evolved than other parts of the brain. These evolutions have resulted due to the influence of environmental demands. Some behaviours play an obvious role in evolution.

For example, the ability to find food, avoid predators, and defend one’s young are the objectives related to the survival of the organisms as well as their species. The biological and behavioural qualities, which are helpful in meeting these objectives, increase an organism’s ability to pass it on to the future generation through its genes. The environmental demands lead to biological and behavioural changes over a long period of time. B IOLOGICAL AND C ULTURAL R OOTS An important determinant of our behaviour is the biological structures that we have inherited from our ancestors in the form of developed body and brain.

The importance of such a biological bases becomes obvious when we observe cases in which brain cells have been destroyed by any disease, use of drug or an accident. Such cases develop various kinds of physical and behavioural disabilities. Many children develop mental retardation and other abnormal symptoms due to transmission of a faulty gene from the parents. As human beings, we not only share a biological system, but also certain cultural systems.

These systems are quite varied across human populations. All of us negotiate our lives with the culture in which we are born and brought up. Culture provides us with different experiences and opportunities of learning by putting us in a variety of situations or placing different demands on our lives. Such experiences, opportunities and demands also influence our behaviour considerably.

These influences become more potent and visible as we move from infancy to later years of life. Thus, besides biological bases, there are cultural bases of behaviour also. You will learn about the role of culture in behaviour at a later point in this chapter. B IOLOGICAL B ASIS OF B EHAVIOUR Neurons Neuron is the basic unit of our nervous system.

Neurons are specialised cells, which possess the unique property of converting various forms of stimuli into electrical impulses. They are also specialised for reception, conduction and transmission of information in the form of electrochemical signals. They receive information from sense organs or from other adjacent neurons, carry them to the central nervous system (brain and spinal cord), and bring motor information from the central nervous system to the motor organs (muscles and glands). Nearly billion neurons are found in the human nervous system.

They are of many types and vary considerably in shape, size, chemical composition, and function. Despite these differences, they share three fundamental components, i.e. soma, dendrites, and axon. The soma or cell body is the main body of the nerve cell.

It contains the nucleus of the cell as well as other structures common to living cells of all types (Figure . ). The genetic material of the neuron is stored inside the nucleus and it becomes actively engaged during cell reproduction and protein synthesis. The soma also contains most of the cytoplasm (cell- fluid) of the neuron.

Dendrites are the branch- like specialised structures emanating from the soma. They are the receiving ends of a neuron. Their function is to receive the incoming neural impulses from adjacent neurons or directly from the sense organs. On dendrites are found specialised receptors, which become active when a signal arrives in electrochemical or biochemical form.

The received signals are passed on to soma and then to axon so that the information is relayed to another neuron or to muscles. The axon conducts the information along its length, which can be several feet in the spinal cord and less than a millimeter in the brain. At the terminal point the axon branches into small structures, called terminal buttons . These buttons have the capability for transmitting information to another neuron, gland and muscle.

Neurons generally conduct information in one direction, that is, from the dendrites through soma and axon to the terminal buttons. The conduction of information from one place to another in the nervous system is done through nerves, which are bundles of axons . Nerves are mainly of two types: sensory and motor . Sensory nerves, also called afferent nerves, carry information from sense organs to central nervous system.

On the other hand, motor nerves, also called efferent nerves, carry information from central nervous system to muscles or glands. A motor nerve conducts neural commands which direct, control, and regulates our movements and other responses. There are some mixed nerves also, but sensory and motor fibers in these nerves are separate. Nerve Impulse Information travels within the nervous system in the form of a nerve impulse.

When stimulus energy comes into contact with receptors, electrical changes in the nerve potential start. Nerve potential is a sudden change in the electrical potential of the surface of a neuron. When the stimulus energy is relatively weak, the electrical changes are so small that the nerve impulse is not generated, and we do not feel that stimulus. If the stimulus energy is relatively strong, electrical impulses are generated and conducted towards the central nervous system.

The strength of the nerve impulse, however, does not depend on the strength of the stimulus that started the impulse. The nerve fibers work according to the “ all or none principle ”, which means that they either respond completely or do not respond at all. The strength of the nerve impulse remains constant along the nerve fiber. Synapse Information is transmitted from one place to another within the nervous system in the form of a neural impulse.

A single neuron can carry a neural impulse up to a distance covered by the length of its axon. When the impulse is to be conducted to a distant part of the body, a number of neurons participate in the process. In this process, one neuron faithfully relays the information to a neighboring neuron. The axon tip of a preceding neuron make functional connections or synapse with dendrites of the other neuron.

A neuron is Fig. . : The Structure of Neuron Nucleus Terminal buttons Dendrites (receiving end) Soma Cytoplasm Axon (transmitting) Myelin sheath Nodes of ranvier functions. Based on location, the nervous system can be divided into two parts: Central Nervous System (CNS) and Peripheral Nervous System (PNS).

The part of the nervous system found inside the hard bony cases (cranium and backbone) is classified as CNS. Brain and spinal cord are the organs of this system. The parts of the nervous system other than central nervous system are placed in the PNS. PNS can be further classified into Somatic and Autonomic nervous system.

Somatic nervous system is concerned with voluntary actions, while the autonomic nervous system performs functions on which we have no voluntary control. The organisation of the nervous system is schematically presented in Figure . . never physically connected with another neuron; rather there is a small gap between the two.

This gap is known as synaptic cleft. The neural impulse from one neuron is transmitted by a complex synaptic transmission process to another neuron. The conduction of neural impulse in the axon is electrochemical, while the nature of synaptic transmission is chemical (Figure . ).

The chemical substances are known as neurotransmitters. S TRUCTURE AND F UNCTIONS OF N ERVOUS S YSTEM AND E NDOCRINE S YSTEM AND THEIR R ELATIONSHIP WITH B EHAVIOUR AND E XPERIENCE Since our biological structures play an important role in organisation and execution of behaviour, we shall look at these structures in some detail. In particular, you will read about the nervous system and the endocrine system, which work together in giving a shape to human behaviour and experience. The Nervous System Human nervous system is the most complex and most developed of all living creatures.

Though the nervous system functions as a whole, for the ease of study, we can divide it into many parts depending on its location or Fig. . : Transmission of Nerve Impulse through Synapse Terminal button Synaptic vesicles Synaptic cleft Neurotransmitter Dendrite Fig. .

: Schematic Representation of the Nervous System Spinal Cord (Ascending Pathways, Interneurons, and Descending Pathway) Somatic Nervous System (SNS) (Sensory and Motor Nerves, Voluntary) Brain (Hindbrain, Midbrain, and Forebrain) Sympathetic Division (Trouble Shooter) Parasympathetic Division (Housekeeping) Autonomic Nervous System (ANS) (Internal System, Involuntary) Nervous System Central Nervous System (CNS) Peripheral Nervous System (PNS) (Neural Tissue outside Brain and Spinal Cord) Endocrine System The Peripheral Nervous System The PNS is composed of all the neurons and nerve fibers that connect the CNS to the rest of the body. The PNS is divided into Somatic Nervous System and Autonomic Nervous System. The autonomic nervous system is further divided into Sympathetic and Parasympathetic systems. The PNS provides information to the CNS from sensory receptors (eyes, ears, skin, etc.) and relays back motor commands from the brain to the muscles and glands.

The Somatic Nervous System This system consists of two types of nerves, called cranial nerves and spinal nerves. There are twelve sets of cranial nerves which either emanate from or reach different locations of the brain. There are three types of cranial nerves - sensory, motor, and mixed. Sensory nerves collect sensory information from receptors of the head region (vision, audition, smell, taste, touch, etc.) and carry them to the brain.

The motor nerves carry motor impulses originating from the brain to muscles of the head region. For example, movements of the eyeballs are controlled by motor cranial nerves. Mixed nerves have both sensory and motor fibers, which conduct sensory and motor information to and from the brain. There are thirty one sets of spinal nerves coming out of or reaching to the spinal cord.

Each set has sensory and motor nerves. Spinal nerves have two functions. The sensory fibers of the spinal nerves collect sensory information from all over the body (except the head region) and send them to the spinal cord from where they are then carried out to the brain. In addition, motor impulses coming down from the brain are sent to the muscles by the motor fibers of the spinal nerves.

The Autonomic Nervous System This system governs activities which are normally not under direct control of individuals. It controls such internal functions as breathing, blood circulation, salivation, stomach contraction, and emotional reactions (Figure . ). These activities of the autonomic system are under the control of different structures of the brain.

The Autonomic Nervous System has two divisions: Sympathetic division and Parasympathetic division. Although the effect Parasympathetic Stimulates tear glands Dilates pupil Inhibits salivation Increases sweating Accelerates heart Dilates bronchi Decreases digestive functions of stomach Secretes adrenaline Decreases digestive functions of intestine Inhibits bladder Spinal cord Chain of sympathetic ganglia Fig. . : The Functions of the Autonomic Nervous System Constricts pupil Inhibits tear gland Increases salivation Slows heart Constricts bronchi Increases digestive functions of stomach Increases digestive functions of intestine Contracts bladder Sympathetic Brain scanning reveals that while some mental functions are distributed among different areas of the brain, many activities are localised also.

For example, the occipital lobe of the brain is a specialised area for vision. of one division is opposite to the effect of the other, both work together to maintain a state of equilibrium. The sympathetic division deals with emergencies when the action must be quick and powerful, such as in situations of fight or flight. During this period, the digestion stops, blood flows from internal organs to the muscles, and breathing rate, oxygen supply, heart rate, and blood sugar level increases.

The Parasympathetic division is mainly concerned with conservation of energy. It monitors the routine functions of the internal system of the body. When the emergency is over, the parasympathetic division takes over; it decelerates the sympathetic activation and calms down the individual to a normal condition. As a result all body functions like heart beat, breathing, and blood flow return to their normal levels.

The Central Nervous System The central nervous system (CNS) is the centre of all neural activity. It integrates all incoming sensory information, performs all kinds of cognitive activities, and issues motor commands to muscles and glands. The CNS comprises of the (a) brain and (b) spinal cord. You will now read about the functions of the major parts of the brain and for what behaviours is each part responsible.

The Brain and Behaviour It is believed that the human brain has evolved over millions of years from the brains of lower animals, and this evolutionary process still continues. We can examine the levels of structures in the brain, from its earliest to the most recent form in the process of evolution. The limbic system, brain stem and cerebellum are the oldest structures, while Cerebral Cortex is the latest development in the course of evolution. An adult brain weighs about .

kg and contains around billion neurons. However, the most amazing thing about the brain is not its number of neurons but its ability to guide human behaviour and thought. The brain is organised into structures and regions that perform specific functions. Ask some students to make small slips of paper and write names of the parts of the nervous system on them.

Put the slips together in a bowl and ask the students from the class to pick one slip each. Give them a few minutes and ask them to learn the location and function of the part mentioned in the slip. Each student is to then come forward and introduce him/herself as that part and explain the location and functions of that part. Activity .

Structure of the Brain For the convenience of study, the brain can be divided into three parts: Hindbrain, Midbrain and Forebrain (Figure . ). Hindbrain This part of the brain consists of the following structures: Medulla Oblongata : It is the lowest part of the brain that exists in continuation of the spinal cord. It contains neural centres, which Fig.

. : Structure of the Brain Hypothalamus Pituitary gland Thalamus Cerebrum (cerebral cortex) Pineal gland Brainstem Midbrain Pons Medulla oblongata Spinal cord Cerebellum a vital role in our behaviour. It regulates physiological processes involved in emotional and motivational behaviour, such as eating, drinking, sleeping, temperature regulation, and sexual arousal. It also regulates and controls the internal environment of the body (e.g., heart rate, blood pressure, temperature) and regulates the secretion of hormones from various endocrine glands.

Thalamus : It consists of an egg-shaped cluster of neurons situated on the ventral (upper) side of the hypothalamus. It is like a relay station that receives all incoming sensory signals from sense organs and sends them to appropriate parts of the cortex for processing. It also receives all outgoing motor signals coming from the cortex and sends them to appropriate parts of the body. The Limbic System : This system is composed of a group of structures that form part of the old mammalian brain.

It helps in maintaining internal homeostasis by regulating body temperature, blood pressure, and blood sugar level. It has close links with the hypothalamus. Besides hypothalamus, the limbic system comprises the Hippocampus and Amygdala. The hippocampus plays an important role in long-term memory.

The amygdala plays an important role in emotional behaviour. The Cerebrum : Also known as Cerebral Cortex , this part regulates all higher levels of cognitive functions, such as attention, perception, learning, memory, language behaviour, reasoning, and problem solving. The cerebrum makes two-third of the total mass of the human brain. Its thickness varies from .

mm to mm, which covers the entire surface of the brain and contains neurons, neural nets, and bundles of axons. All these make it possible for us to perform organised actions and create images, symbols, associations, and memories. The cerebrum is divided into two symmetrical halves, called the Cerebral Hemispheres. Although the two hemispheres appear identical, functionally one hemisphere usually dominates the other.

For example, the left hemisphere usually controls language regulate basic life supporting activities like breathing, heart rate, and blood pressure. This is why medulla is known as the vital centre of the brain. It has some centres of autonomic activities also. Pons : It is connected with medulla on one side and with the midbrain on the other.

A nucleus (neural centre) of pons receives auditory signals relayed by our ears. It is believed that pons is involved in sleep mechanism, particularly the sleep characterised by dreaming. It contains nuclei affecting respiratory movement and facial expressions also. Cerebellum : This highly developed part of the hindbrain can be easily recognised by its wrinkled surface.

It maintains and controls posture and equilibrium of the body. Its main function is coordination of muscular movements. Though the motor commands originate in the forebrain, the cerebellum receives and coordinates them to relay to the muscles. It also stores the memory of movement patterns so that we do not have to concentrate on how to walk, dance, or ride a bicycle.

Midbrain The midbrain is relatively small in size and it connects the hindbrain with the forebrain. A few neural centres related to some special reflexes and visual and auditory sensations are found here. An important part of midbrain, known as Reticular Activating System (RAS), is responsible for our arousal. It makes us alert and active by regulating sensory inputs.

It also helps us in selecting information from the environment. Forebrain It is considered to be the most important part of the brain because it performs all cognitive, emotional, and motor activities. We will discuss four major parts of the forebrain: hypothalamus, thalamus, limbic system, and cerebrum. Hypothalamus : The hypothalamus is one of the smallest structures in the brain, but plays behaviour.

The right hemisphere is usually specialised to deal with images, spatial relationships, and pattern recognition. These two hemispheres are connected by a white bundle of myelinated fibers, called Corpus Callosum that carries messages back and forth between the hemispheres. Cerebral cortex has also been divided into four lobes - Frontal lobe, Parietal lobe, Temporal lobe, and Occipital lobe. The Frontal lobe is mainly concerned with cognitive functions, such as attention, thinking, memory, learning, and reasoning, but it also exerts inhibitory effects on autonomic and emotional responses.

The Parietal lobe is mainly concerned with cutaneous sensations and their coordination with visual and auditory sensations. The Temporal lobe is primarily concerned with the processing of auditory information. Memory for symbolic sounds and words resides here. Understanding of speech and written language depends on this lobe.

The Occipital lobe is mainly concerned with visual information. It is believed that interpretation of visual impulses, memory for visual stimuli and colour visual orientation is performed by this lobe. Physiologists and psychologists have tried to identify specific functions associated with specific brain structures. They have found that no activity of the brain is performed only by a single part of the cortex.

Normally, other parts are involved, but it is also correct that there is some localisation of functions, i.e. for a particular function, a particular part of the cortex plays a more important role than the other parts. For example, if you are driving a car, you see the road and other vehicles by the function of your occipital lobe, hear the horns by the function of your temporal lobe, do many motor activities controlled by parietal lobe, and make decisions by the help of frontal lobe. The whole brain acts as a well coordinated unit in which different parts contribute their functions separately.

Spinal Cord The spinal cord is a long rope-like collection of nerve fibers, which run along the full length inside the spine. Its one end is connected with the medulla of the brain and another is free at the tail end. Its structure all along its length is similar. The butterfly shaped mass of grey matter present in the centre of the spinal cord contains association neurons and other cells.

Surrounding the grey matter is the white matter of the spinal cord, which is composed of the ascending and descending neural tracts. These tracts (collections of nerve fibers) connect the brain with the rest of the body. The spinal cord plays the role of a huge cable, which exchanges innumerable messages with the CNS. There are two main functions of the spinal cord.

Firstly, it carries sensory impulses coming from the lower parts of the body to the brain; and motor impulses originating from the brain to all over the body. Secondly, it performs some simple reflexes that do not involve the brain. Simple reflexes involve a sensory nerve, a motor nerve, and the association neurons of the grey matter of the spinal cord. Reflex Action A reflex is an involuntary action that occurs very quickly after its specific kind of stimulation.