Other Growth Changes

Some alterations in tissue growth are not cancerous. Atrophy, for example, is a lessening in size. It is the shrinking of cells or tissues for various reasons. Starvation, for instance, causes atrophy of the adipose, or fatty, tissues. Disuse of a body part may also lead to atrophy. When a fractured arm is placed in a cast, the arm’s muscles decrease in size from lack of use.

Compensatory hypertrophy, in medicine, condition that results when one of a paired set of organs, such as a kidney or a lung, is removed and the remaining organ increases in size.

Hypertrophy is an increase in size of individual cells or fibres It results in an enlargement of the body part containing these muscles or fibres Hypertrophy of the heart has already been discussed. Compensatory hypertrophy is best seen in paired organs. When a diseased kidney is removed from the body, the remaining kidney grows larger because it now must do the work of two kidneys.

RESPIRATORY SYSTEM DISEASES

The lungs are spongy organs through which vital oxygen enters the body and needless carbon dioxide exits. Oxygen and carbon dioxide are exchanged in and out of capillaries in the many tiny air sac’s, or alveoli, in the lungs. Although the breathing passages have defences against invading germs and irritants, the lungs can be stricken by a number of serious diseases.

Chronic bronchitis is a disease that results from infection of the air passages by bacteria or viruses. It is marked by cough and increased production of sputum, an accumulation of saliva, mucus, and pus. Air pollution and cigarette smoking both can aggravate the malady.

Tuberculosis, bacterial disease most frequently affecting lungs; associated with fever and loss of weight; commonly transmitted through the air (droplet infection) but also from drinking unpasteurized milk obtained from infected cows.

Tuberculosis is a complicated disease that most often strikes the lungs. The bacilli that cause it grow from place to place in the lung, leaving cavities in the unoccupied sites.

Symptoms of tuberculosis may include weight loss, fever, chest pain, cough, and sputum. After the active infection is arrested, a period follows when the disease may break out again. Tuberculosis is treated with isoniazid and other drugs.

Pneumonia, or acute infection of the lungs, may occur suddenly in a seemingly healthy person. It is usually marked by fever, cough, and chest pain. Lung X rays show patches of inflammation. Though once quite fatal, the threat of pneumonia has been reduced as a result of antibiotic treatment.

Pleurisy, an inflammation of the pleura; caused by infection, injury, or other chest diseases.

Pleura, the serous membrane that covers the lungs, lines the walls of the thorax, and is reflected upon the diaphragm.

Pleurisy is severe chest pain accompanying each deep breath in a person with an inflamed pleura, the twin membrane around each lung and lining the chest cavity. Pleurisy can attend pneumonia or result from direct infection of the pleura.

Emphysema is a serious lung disease that follows destruction of the elastic and connective tissue fibres supporting the lung. It is linked with advancing age. Certain forms of emphysema are inherited. Heavy cigarette smoking and long exposure to air pollutants seem to encourage the disease. A person with emphysema, lacking sufficient lung elasticity, wheezes and has trouble breathing. Furthermore, air movement in the lungs is reduced and the patient is easily fatigued because he fails to get enough oxygen or get rid of enough carbon dioxide.

Asthma is the wheezing or whistling sound that accompanies each breath when the air passages contain too much mucus. It may follow lung infection or result from an allergic reaction that causes muscle spasms and swelling in the air passages.

Acute pulmonary oedema results when fluid quickly accumulates in the lungs and fills the alveoli. The fluid build-up is caused by heart trouble that, in turn, produces back pressure in the pulmonary veins and the left atrium of the heart to which they carry oxygen-rich blood from the lungs. A person suffering acute pulmonary oedema is suddenly breathless and turns blue because of oxygen-poor blood. The condition is treated with oxygen, digitalis to strengthen heart action, and diuretics to speed fluid removal by the kidneys.

Pneumothorax, presence of air in the usually air-free pleural space between the lungs and chest walls.

Pneumothorax occurs when air gets into the chest between the pleural lining. The lung then collapses. A collapsed lung may occur when the chest is pierced in some way or when an abnormal bleb, or blister, on the lung surface bursts.

Lung abscess is an accumulation of a mass of pus inside the lung. A lung abscess can increase the seriousness of pneumonia and other lung infections, especially in chronically ill persons.

Hyaline membrane disease is a disorder of some prematurely born infants. The alveoli of afflicted babies are lined with a protein material, limiting the amount of oxygen their blood can receive. The disease is often fatal.

Histoplasmosis is a fungus infection of the lungs. Fungi lodge in the lungs and multiply until body defences wall them off. In some areas it was once called “summer flu” because its symptoms resemble those of influenza. Serious cases involve weight loss and a long convalescent period.

Silicosis, disease of the lungs, caused by inhaling tiny sharp particles of stone dust; fibrous tissue forming around particles causes cough, shortness of breath, and weakness.

Pneumoconiosis means “dust disease.” It can strike miners and industrial workers who inhale damaging amounts of dust. One of the most serious is silicosis, which results from inhaling quartz dust. Another, anthracosilicosis, arises from inhalation of coal and quartz dust.

SKIN DISEASES

Because of its location the skin is perhaps more susceptible to disease than any other body organ. Even so, it is marvellously designed for its particular jobs of protecting the inner body against harm from the outside surroundings, receiving clues about what is happening externally, and keeping the body cool by means of the evaporation of sweat produced by its sweat glands. The skin is thick, leathery, and tough enough to prevent mechanical injury to the body. It is also covered with a barrier of dead cells that block harmful chemicals from getting into the body.

The skin is richly supplied with nerves that enable the perception of pain, touch, heat, and cold. Blood vessels in the skin can either contract or expand in response to nerve signals. A person’s emotional state can often be observed through changes in skin colour Shame or rage reddens the skin; fear blanches it. The skin may react to disease in a great many ways including formation of blisters, pimples, ulcers, tumours, and by haemorrhage

Blackheads are an accumulation of a horny material in special follicles of the face. The characteristic black dots in blackheads are not dirt but melanin, the pigment responsible for skin colour

Acne is an outcropping of blackheads or pimples on the face of an adolescent. It is brought on by hormonal changes that accompany sexual maturity. It is not caused by food, emotions, or uncleanliness. Antibiotics are available for the treatment of severe acne, but most cases respond well to local application of a peeling agent.

Warts are horny growths caused by virus infection. They are spread from person to person. Although warts cannot be prevented, they can be burned away with an electric needle or a caustic chemical such as nitric acid.

Hives, or urticaria, are itchy, whitish elevations of the skin. They appear and disappear rapidly. Hives are often the result of an allergic reaction to certain foods or medicines. Persons who suffer severe cases of hives can receive a series of desensitizing shots. Antihistamine drugs sometimes can relieve a bout of hives.

Birthmark, a skin blemish, result of an overgrowth of blood vessels.

Birthmarks are the result of an overgrowth of blood vessels. They usually show up after birth as port-wine-coloured stains or strawberry-coloured marks. The strawberry marks may eventually disappear but at times can be destroyed quickly by the application of extreme cold. Port-wine stains and other long-lasting skin blemishes can be concealed by special cosmetics.

Eczema, or dermatitis, is a superficial inflammation of the skin. It can be an allergic reaction to poison ivy, dyes, or drugs. It can be provoked by such irritants as acids, solvents, or excessive use of soap or detergents. Sunburn can also cause eczema. Some forms of it, such as infantile eczema and seborrhoeic dermatitis, stem from an unknown cause. Nonetheless, nearly all types of eczema can be relieved by the application of corticosteroid creams.

Athlete’s foot is a fungus infection of the skin between the toes. The infected area is scaly, moist, and itchy. It usually has a disagreeable smell. Athlete’s foot can be relieved when anti fungal drugs are applied to the infected skin each day. Fungus infections that cause a loss of hair or nails must be treated with griseofulvin, an antibiotic.

Bacterial infections such as the psoriasis caused by “staphylococci” germs are rare because of modern standards of hygiene and sanitation. However, the bacterial disease gonorrhoea, which passes between the skin of the sex organs, has risen to epidemic proportions among teenagers in recent years. This and other bacterial infections of the skin are remedied with antibiotics.

NERVOUS SYSTEM DISEASES

The nervous system is the quick communication system of the body. Information from the outside world enters the body through the sense organs and is sent to the spinal cord for instant response or is relayed to the brain for further processing.

Nerves and the membranes that protect portions of the nervous system are susceptible to breakdown or infection. Sometimes, the organisms that cause such diseases as mumps or infectious hepatitis can infect the nervous system, too.

Nervous System Infections

Meningitis is an inflammation of the meninges, or membranes around the brain and spinal cord. It can occur through viruses, bacteria, fungi, or yeasts that get into the nervous system. Meningitis is a serious disease and can be fatal.

Shingles, inflammation of certain nerve tissue caused by virus herpes zoster.

Shingles, or herpes zoster, is a virus-caused inflammation of certain nerve tissue. Painful skin bumps occur over the line of the inflamed nerve or its branches. Shingles and chicken pox are both caused by the same virus.

Non-infectious Nerve Disorders

Neuritis, disease of the nerves causing pain, abnormal circulation, and reflex action; differs from neuralgia because of inflammation; treatment includes heat, proper nutrition, physical therapy, and medication.

Neuritis is the degeneration of one or more nerves. It is often marked by a pins-and-needles feeling, a burning sensation, or a stabbing pain. Neuritis can result from infection, especially of the facial nerve, hard body blows, or bone fracture causing nerve injury. Everyday hard grasping of tools and activities requiring cramped body positions can also trigger neuritis.

Neuralgia, severe, stabbing pain along course of nerve; not associated with nerve damage; attacks often triggered by infection, malnutrition, chilling, or fatigue; sometimes is symptom of organic disease; trigeminal neuralgia, popularly called tic douloureux, affects main sensory nerve of face and is treated by local anaesthetic or cutting of nerve roots.

Neuralgia is often confused with neuritis but is a distinct problem. Neuralgia is characterized by sudden, sharp bursts of pain along any of the sensory nerves near the body surface.

Sciatica is severe leg pain resulting from an inflamed sciatic nerve or its branches. A ruptured, or “slipped,” disk one of the pads between the vertebra of the spine often causes sciatica.

Tics are usually habitual muscle twitches in the face or neck that seem to serve no purpose. A tic is generally intensified by an emotional situation or by fatigue.

Vertigo, a severe form of dizziness resulting from the inability of the body to adapt to abrupt or unexpected motion.

Vertigo is a dizziness or disorientation that occurs when something is wrong with the body’s balancing system, part of which is located in the inner ear. The sufferer feels as though he is falling through space.

Parkinson’s disease (or paralysis agitans, or Parkinsonism), chronic disorder of nervous system, manifest by tremors and muscle weakness, accompanied by changes in pigmented cells of brain stem; strikes in middle or late life; treated with drugs and sometimes by brain surgery; named for James Parkinson (1755-1824), British physician who identified it in 1817.

Parkinsonism, or Parkinson’s disease, is thought to stem from changes in brain chemistry. Victims of the disorder walk with a slow, shuffling gait, have a wide-eyed, unblinking facial look, and experience muscle tremors, or shakes. They also have trouble speaking and swallowing. Parkinsonism can be treated with a drug called levodopa, or L-dopa.

Multiple sclerosis (MS), chronic disease of the nervous system; cause unknown; leads to disturbances of vision, speech, coordination, and bodily functions.

Multiple sclerosis is a slow-developing disease that eventually involves the entire brain and spinal cord. Its cause is not yet known, but the disease eats away the fatty myelin sheath around many nerves. As a result, it interferes with proper nerve-signal transmission to muscles and organs. Muscle control, vision, mental abilities, and many other body functions are eventually impaired. Physical therapy is often required because the limbs of victims become weak and they are easily tired doing ordinary tasks.

Stroke

Stroke (or cardiovascular accident), common term for cerebral thrombosis (a blood clot that interrupts the blood supply of the brain) and for cerebral haemorrhage (a rupture in a blood vessel that allows blood to escape into the brain tissue); both can cause brain damage with resulting paralysis or death.

A stroke, or cardiovascular accident, occurs when blood can no longer nourish brain tissue and key nerve cells are thereby destroyed. A blood clot in one of the brain’s blood vessels, haemorrhage from a broken blood vessel there, or hardening of a brain artery can cause a stroke.

Depending upon the brain area affected, a stroke can culminate in loss of limb use particularly the arms speech difficulties, and partial blindness. In time, victims of relatively non severe strokes often regain most or all of the impaired body functions. In more severe cases, extensive physical or speech therapy is needed for partial rehabilitation of the stroke victim.

Epilepsy

Epilepsy, disease of the nervous system, frequently from subtle brain damage, less often from injury; characterized by sudden, recurrent seizures with loss of consciousness and severe convulsions (grand mal), or in mild form by brief blackouts and fainting spells (petit mal).

Epilepsy is a brain disorder in which nerve signals “fire” abnormally and cause convulsive seizures, or alternating muscle contractions and relaxations. Scar tissue in the brain can provoke some seizures. In many cases, however, doctors cannot pinpoint the reason for an epileptic attack. Someone might have a seizure once and never again. If someone has more than one seizure, the second and any that may follow are officially called epileptic attacks.

Doctors generally recognize several types of epilepsy, including grand mal, petit mal, and infantile spasms. A grand mal attack is usually marked by rigidly contracted muscles, loss of consciousness, and collapse. The attack may last from two to five minutes, followed by deep sleep.

A petit mal attack usually comes as a lapse of awareness for less than a minute. The victim then resumes whatever activity he was engaged in before the attack without realizing anything out of the ordinary took place. Infants under the age of three sometimes have infantile spasms during which sharp muscle contractions force the body to jackknife for a few seconds. Anti convulsive drugs are used to treat and prevent all such attacks.

METABOLIC AND DEFICIENCY DISEASES

Disease can sometimes follow from alterations in normal body metabolism caused by deficiencies in diet, hormones, and vitamins. It can also stem from malfunctions in the body’s immunity system.

Malnutrition and Vitamin Deficiencies

Malnutrition can be either over nutrition or under nutrition Obesity resulting from overeating can lead to high blood pressure, heart disease, and diabetes. Under eating can stifle the development of body and mind.

Marasmus is the condition that results when a child’s diet lacks both total calories and protein. A child with marasmus is always hungry and wastes away. Kwashiorkor is a protein deficiency that saps a child’s strength even though his diet contains enough calories. A child with kwashiorkor lacks an appetite and is sullen. Both conditions occur in underdeveloped nations.

Vitamin deficiencies are uncommon among people in the world’s richer nations, except in the cases of pregnant women and those who breast-feed their babies. Since ample vitamins are in the general diet in those lands, there is no medical justification for daily doses of multivitamins to stimulate vigour or prevent colds or infections.

Iron, silver-grey, hard, brittle, fusible element that is the cheapest and most used of all metals. In pure form it is very reactive chemically and rapidly corrodes in moist air and warm temperatures. Iron is often alloyed with other metals to make it tough yet malleable. Pig iron is used to produce steel. The use of iron is prehistoric

Properties of Iron

Symbol Fe

Atomic number 26

Atomic weight 55.8

Group in periodic table VIII

Boiling point 4,982 F (2,750 C)

Melting point 2,795 F (1,535 C)

Specific gravity 7.874

Mineral deficiencies can also produce body disorders. Iron is indispensable for the prevention of anaemia Magnesium is a cofactor in many enzymes. Deficiency of it causes dizziness, weakness, and convulsions. Iodine is a major part of the thyroid hormones. Without it a person can develop a goitre Fluorine is not considered essential, but it plays a great part in minimizing dental caries, or cavities. Trace elements, such as chromium, cobalt, and manganese are also needed for a healthy body.

Hormone Deficiencies

The body’s endocrine system produces a variety of hormones. When the endocrine glands are not working properly, certain disease processes can begin.

Abnormal output of growth hormone from the pituitary gland early in life can result in one of two disorders dwarfism if there is too little or gigantism if there is too much. Abnormal output of certain hormones from the adrenal glands causes irregular regulation of the body’s water balance and disturbs the normal retention and excretion of salts. Malfunction in sex hormone production can stem sexual activity, as well as produce excessive hair growth and distribution. Malfunction of the thyroid gland affects the rate at which food is burned for energy, causing the metabolic rate to run too fast or too slow for everyday needs. When part of the pancreas breaks down, diabetes develops.

1921: Insulin found to treat diabetes. In 1921, at the University of Toronto, Frederick Grant Banting and Charles H. Best conducted experiments that successfully isolated the hormone insulin. This hormone is used to control the disease diabetes. The name of the hormone is derived from the Latin word for island, insula, because the hormone is produced in the part of the pancreas called the Islets of Langerhans.

Although it had been known for some time that the pancreas made the enzymes responsible for digesting proteins, it had not been possible to isolate insulin. Insulin is a protein and is digested by the enzymes. Banting and Best used animal experiments to extract insulin and demonstrated that it stopped symptoms of diabetes. Commercial production of insulin uses pigs, oxen, and sheep as sources for the hormone.

Diabetes Mellitus

Diabetes mellitus, a fairly common disease, is caused by lack of biologically active insulin, a hormone secreted by the pancreas. Without insulin the body cannot use sugars and starches in the food. It must then rely upon its stored fat for energy. This storehouse is soon exhausted, however, because without insulin the body can no longer make and store fat. In addition, protein is no longer manufactured and the muscle mass of the body dwindles. The effect of growth hormone is reduced too. All this adds up to a rise in the level of blood sugar and increased urination, which, in turn, dehydrates the body and makes the diabetic thirsty. The sufferer loses weight, experiences muscle cramps, and has an itchy skin. If diabetes is not treated, sodium and potassium are lost in the urine and the products of fat breakdown, called ketones, build up in dangerous proportions in the blood. The blood also becomes increasingly acid and body dehydration reaches a dangerous level. Finally, the untreated diabetic goes into a potentially fatal coma.

Diabetes is treated by limiting the patient’s diet and injecting him with insulin derived from cattle or hog pancreases. This treatment was pioneered by the Canadian physicians Frederick G. Banting and Charles H. Best in the 1920s.

Recently, an oral medication has proved capable of lowering the blood sugar of diabetics who develop a mild form of the disease after they reach adulthood. These tablets do not contain insulin but are helpful as long as the pancreas of the diabetic still produces some insulin.

Long-term diabetes is often associated with blood vessel degeneration. When this complication occurs, the diabetic can suffer heart disease, stroke, eye haemorrhage and blindness, kidney failure, gangrene of the feet, and serious neuritis.

The normal blood-sugar level ranges between 60 and 100 milligrams per 100 cubic centimetres of blood. It rises slightly higher after a meal. When the level falls below normal, a person has hypoglycaemia and may develop headache, irritability, sweatiness, and other symptoms. Later, the patient has trouble keeping balance, speaks incoherently, and may even become violent or act listless and withdrawn. Finally, the hypoglycaemic person falls into a coma and may have convulsions.

A diabetic may experience hypoglycaemia when he gets an excessive dose of insulin or oral medication. Hypoglycaemia can also result from diseases of the adrenal, pituitary, and pancreas glands, as well as from starvation, liver damage, and alcohol intake. Moreover, some otherwise healthy persons, especially those under too much stress, can suffer mild hypoglycaemia In an emergency, a health care provider may administer sugar, either orally or by intravenous injection. Glucagon, a pancreatic hormone that raises the blood-sugar level, can also be injected. Long-range treatment involves correcting the disorder engendering the low blood sugar. People suffering from hypoglycaemia often respond very favourably to a change in diet that balances sugar and other nutrients.

Man has always been fascinated by the amazingly varied behaviour of animals. Ancient man observed the habits of animals, partly out of curiosity but primarily in order to hunt and to domesticate some animals. Most people today have a less practical interest in animal behaviour They simply enjoy the antics and activities of pets, of animals in zoos, and of wildlife. But in modern times animal behaviour has also become a scientific speciality The biologists and psychologists who study animal behaviour try to find out why animals act in the specific ways they do and how their behaviour helps them and their offspring survive. Some of them feel that the behaviour of animals provides clues to the behaviour of man.

Anthropomorphism, the ascribing of human form or qualities to gods or things, as when ancient people attributed powers to fire, stones, and trees, and as animals in fables have the gift of speech.

A great deal of fanciful “animal lore” has arisen over the years in the mistaken belief that animals behave for the same reasons as man. The view that non-human things have human attributes is called anthropomorphism. An example of anthropomorphism is found in the following passage written by the 1st century AD Roman author Pliny the Elder:

The largest land animal is the elephant. It is the nearest to man in intelligence; it understands the language of its country and obeys orders, remembers duties that it has been taught, is pleased by affection and by marks of honour, nay more it possesses virtues rare even for man, honesty, wisdom, justice, also respect for the stars and reverence for the sun and moon.

Undeniably, the elephant can be taught to perform certain tasks, but no one today seriously believes that it reveres the sun and the moon.

Animal behaviour can be studied in natural settings or in the laboratory. Often, laboratory experiments are designed to test notions based on outdoor observation. The study of animal behaviour from the viewpoint of observing instinctive behaviour in the animal’s natural habitat is called ethology. (The ways in which animals solve their common problems for example, eating, drinking, protecting themselves and their offspring from predators, reproducing, and grooming are all the concerns of an ethologist, a scientist who studies animal behaviour) A contrasting viewpoint on behaviour, practised in the United States particularly, has concentrated mainly on learning processes, behavioural development, and the influence of behaviour on an animal’s internal workings the action of nerve impulses and hormones, for example. Both approaches are important.

What Is Behaviour?

Simply defined, animal behaviour is anything an animal does its feeding habits, its reproductive actions, the way it rears its young, and a host of other activities. Behaviour is always an organized action. It is the whole animal’s adjustment to changes inside its body or in its surroundings.

The group activities of animals are an important aspect of animal behaviour Bees, for example, communicate with each other about food, and birds may flock during migratory flights. Group activities are often adaptations to a new set of circumstances. Without adaptation, a species could not survive in an ever-changing environment.

Behaviour can also be thought of as a response to a stimulus some change in the body or in the environment. All animals, even those too small to be seen without a microscope, respond to stimuli.

How an Animal Reacts to a Stimulus

A stimulus is a signal from the animal’s body or its environment. It is a form of energy light waves or sound vibrations, for example. All but the simplest animals receive a stimulus light, sound, taste, touch, or smell through special cells called receptors, located in many places on or in the body. For example, fish have taste buds over much of their body, sometimes even on the tail. These buds enable fish to taste the water they swim through and thus to detect nearby food. Cats, which prowl the dark, rely on sensitive touch organs associated with their whiskers.

At the receptors the incoming energy is changed into nerve impulses. In complex animals these impulses may travel either to the brain or through reflex arcs to trigger the hormone or muscle actions of a response.

Conditioning – A Way of Modifying Behaviour

The behaviour of many, perhaps all, animals can be modified by a kind of training called conditioning. Two types of conditioning have been studied classical conditioning and operand conditioning. The first type was discovered by the Russian physiologist Ivan Pavlov; the second, by the American psychologist B.F. Skinner.

In classical conditioning, an animal can be made to respond to a stimulus in an unorthodox manner. For example, a sea anemone can be conditioned to open its mouth when its tentacles are touched a response that it does not ordinarily make to this stimulus. When undergoing such conditioning, an animal is repeatedly offered two different stimuli in timed sequences. The first, called the neutral, or conditioned, stimulus, does not usually cause the animal to respond in the desired way. In the sea anemone experiment, touch is the neutral stimulus. The second, called the unconditioned stimulus, does cause the desired behaviour Squid juice is the unconditioned stimulus because it will cause the sea anemone to open its mouth. In classical conditioning, the neutral stimulus is followed by the unconditioned stimulus. The unconditioned stimulus may be given while the neutral stimulus is being delivered or afterwards The sea anemone was touched first, then given squid juice. After hundreds of such trials, it opened its mouth when touched even though no squid juice was offered.

In operand conditioning, an animal is given some type of reward or punishment whenever it behaves in a certain way for example, whenever it pushes a lever, presses a bar, or moves from one place to another. The reward or punishment, called a reinforcement, follows the action. Food or water may be used as rewards; an electric shock, as a punishment. Rewarding the animal increases the probability that it will repeat the action; punishment decreases the probability. Operand conditioning has been used not only with animals but also in programmed instruction and teaching machines.

Role of the Nervous System in Behaviour

An important relationship exists between an animal’s nervous system and its ability to respond to environmental changes. Animals with a fairly simple nervous system, such as ants, respond in a relatively fixed, or stereotyped, fashion as compared with animals that have a more highly developed and specialized nervous system, such as rats. A rat can link up, or integrate, different stimuli from the environment and can store and use the information from past experience to solve simple and complex problems far better than an ant can. However, the rat does not do as well as a higher mammal, such as a chimpanzee.

For example, a rat, an ant, and a chimpanzee can each learn a complicated pattern of responses to reach food. The rat is trained to run a maze a number of pathways toward a goal, all but one of which end in blind alleys to find food. Then the rat begins at the end of the maze and must learn to run the course backward in order to reach food placed at the starting point. The rat takes less trials to learn the maze backward than forward. An ant given the same training cannot benefit from its past experience. It must learn the backward path as though it were a new one. The chimpanzee shows the greatest learning ability of the three. When the chimpanzee solves a problem, such as discriminating between two geometric shapes, it can do so by generalizing from a “set to learn.” That is, after it has learned that it can obtain food by making the correct choice between the two shapes, it easily makes the correct response on the next try. A rat requires a number of trials before it can associate “shape” with “food.”

The Evolution of Behaviour

Behavioural scientists arrange living things according to the complexity of their behaviour and the extent to which it can be modified. They have found that animals with more complex body and nervous systems have more complex and more modifiable behaviour In addition, however, the behavioural patterns that have evolved among living things are particular ways of adapting to their environments the places where they develop and reproduce. For example, though all animals feed, there are evident differences in the way they feed. Marine worms sift sand for edible organisms. An army ant stings a beetle and brings it back to the colony’s bivouac, where it is dismembered by other members of the colony. A chimpanzee peels a banana before eating it.

It is possible to observe living animals and find out why they act as they do, but can anyone know how extinct animals behaved? There are fossil remains of extinct animals, but behavioural patterns cannot be left as fossils. Yet, equipped only with such fossil remains, scientists can get inklings about the behaviour of extinct species. They achieve this by studying living species in the laboratory or in their natural habitats to determine their behavioural similarities and differences. Then they try to uncover the relationship between the structure of the body parts of these species and the particular function of each body part. Thus, if particular characteristics of the structure of a wing or a leg, for example, can be identified with a particular activity of a living animal, a scientist studying the evolution of behaviour can make plausible guesses about the possible function of fossil bones. He can then develop notions about the possible behaviour of extinct species that were ancestors of certain living animals.

For example, by studying the different groups of passerine, or perching birds, researchers have identified the evolutionary relationships among them. One way is to use tail flick as a taxonomic character a structural trait employed in analysing the relationships among different species. Perching birds flick their tails in a particular way as they move through trees. By analysis of the extent of tail-feather spread during a tail flick and the direction and amount of tail movement, evolutionary relationships can be seen among such passerines as cardinals, buntings, weaver birds, wax bills, and finches.

Evolutionary relationships among species may also be studied by analysing different behavioural patterns. Among the most important behavioural patterns are orientation, social organization, and communication. All species exhibit each of these. However, within species considerable variation exists in the stimuli to which individuals respond, the age at which they respond, and the patterns of their response.