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GENETICS (Part 1 of 3)   Leave a comment

DEFINITION:1 the branch of biology that deals with heredity and variation in similar or related animals and plants 2 the genetic features or constitution of an individual, group, or kind.

April 28, 1994: Biological clock found in mice. Evidence for a so-called biological clock in mice was announced by scientists at Northwestern University in Illinois. It was the first time that a gene governing the daily cycle of waking and sleeping, called the circadian rhythm, had been found in mammals. Previously, genes governing circadian rhythms had been found only in fruit flies and bread mould The biological clock gene in mice was found on mouse chromosome number 5. The chromosomes of all living things hold the DNA, which determines the genetic make-up of each individual. Scientists hoped that this research would someday help them find a similar gene governing the biological clock in humans.

Why do human children resemble their parents? Why do the offspring of any species resemble their parents? Biologists have shown that the factors which cause such resemblances are passed on relatively unaltered from generation to generation by a process called heredity. Resemblances, they say, are transmitted by genes, cell units too tiny to be seen even with a microscope. The branch of biology that deals with genes is called genetics.

Through the ages men have speculated about heredity. In ancient Greece, for example, it was thought that the blood was in some way responsible for the transmission of hereditary traits, and the word “blood” is still often used to mean ancestry. Since the beginning of the 20th century, however, genes have been known to be the carriers of traits, though until the 1940s very little was known about them. Scientists recognized that genes were directly responsible for the characteristics of an organism and that genes were transmitted from parents to offspring. However, they had little idea of the gene structure and composition that made these actions possible.

By the 1950s scientists had learned a great deal about the chemistry of genes. Genes were found to be segments of certain complex molecules located in the cell nucleus. The molecules have the unique ability to duplicate themselves and, in so doing, to pass on body-building instructions to the next generation of a species.

THE ORIGINS OF MODERN GENETICS

Even before the beginnings of written history people were aware of some of the ways in which heredity takes place. The domesticated animals and plants of today are proof of this. Today’s domesticated horses, cattle, dogs, corn, wheat, and cotton differ greatly from their primitive, “wild” ancestors. They are products of the ancient breeders’ art, an art that included the proper selection of parents, well-controlled matings, and the careful choice of the best offspring to further improve a breed.

Early Theories of Heredity

Over the centuries more and more became known about the control of heredity for practical purposes. However, scientists remained baffled about the actual processes of trait transmission. All sorts of what proved to be erroneous explanations were advanced. In the 17th century, for example, a group of biologists called the ovists held that the ovaries of females contained the hereditary material and that the male sperm merely triggered embryonic development. Other scientists were of the opinion that tiny but fully formed creatures were present in the sperm.

Early in the 19th century the French biologist Jean Baptiste Lamarck suggested that traits and abilities acquired during the lifetime of an organism could be transmitted to future generations. This theory was termed “the inheritance of acquired characteristics.” Long before Lamarck, notions of this kind had led expectant mothers to practice the piano, gaze at beautiful pictures, or think “kind” thoughts in the hope that this would affect the character of their unborn children. For similar reasons, many breeders exposed plants and animals to the environmental conditions their breeding programs were intended to combat. Genetic discoveries in the mid-1800s proved Lamarck’s view to be mistaken.

1859: Darwin’s theory of evolution. A heated debate that continues to this day was sparked in 1859 with the publication of Charles Darwin’s ‘On the Origin of Species by Means of Natural Selection’. This work was immediately recognized by the scientific community as a landmark treatise on biology and evolution, but some Christians saw it as a threat to their theology.

Charles Darwin began his observations in December 1831 when, at age 22, he left England for South America aboard the exploratory ship HMS Beagle. During this five-year voyage Darwin observed many species of animals and birds and collected many fossils. His observations on the differences and similarities of species, both living and extinct, led him to ask many questions: Why did some species survive and others die out? Why did certain species live in certain places and not in others? These questions preoccupied him when he returned to England in 1836.

Darwin’s observations led him to doubt the commonly held belief that all the species had been created at once and had remained unchanged through time. The problem was to find out what forces made organisms change. Darwin’s answer was his theory of natural selection: certain members of a species have traits that make them better adapted to their environment. These animals are more successful and therefore have more surviving offspring that inherit these traits. Animals that are not well adapted do not have as many offspring and eventually die out. In this way, species change and certain groups become extinct.

Although Darwin devoted much of his time to his theory of natural selection, he did not publish it for more than 20 years. He knew that his explanation of the species would anger many people, since it did not agree with the dominant Christian theology of the time. Despite early scientific and religious opposition, Darwin’s theory of natural selection is now accepted as the explanation of evolution, at least within the scientific community. However, arguments continue between evolutionists and creationists (those who believe all species were created by God in their present form). Darwin’s theories have indeed changed the way most people view the world, from the evolution of humans to the philosophical bases of science itself.

1865: The birth of genetics. It was unfortunate for the biological sciences that Gregor Mendel was an obscure Austrian monk. His pioneering work in the field of genetics was being done at the time that Charles Darwin’s publications on evolution were beginning to create worldwide controversy, but Mendel’s work would remain unknown for years.

Mendel became an Augustinian monk in 1843, but his abilities in mathematics and the sciences were evident. His experiments on the principles of heredity were begun in about 1856 in what is now Czechoslovakia. By crossing various strains of peas with one another, Mendel found that traits were passed on from generation to generation in what he called “discrete hereditary elements” in sex cells, or gametes.

Mendel reported the results of his experiments to a local society for the study of natural science in 1865 and published his findings in the society’s journal. They were as good as buried there for the next 35 years. Although the journal found its way to libraries in Europe and North America, few paid any attention to his writings. When other botanists obtained results similar to Mendel’s, they began searching through earlier writings on the subject. Only then was Mendel’s 1865 research revealed. His “discrete hereditary elements” are now called genes, and the new science once called Mendelism is known as genetics.

Two Pioneers of Genetics

In 1859 the English biologist Charles Darwin published his epic ‘The Origin of Species’, an attempt to demonstrate that all living things are related through the common bond of evolution. Darwin assumed that all species produce more offspring than reach maturity. Those offspring that survive and reproduce, he reasoned, do so because they are better suited to the existing environment. Because environment changes with time, he argued, species must either adapt to the new conditions or become extinct. Darwin did not know just what mechanisms made it possible for such changes in species to take place. He recognized, however, that if his theory were correct, changeable or mutable units of heredity must exist and that variations in species must arise as a result of an accumulation of small changes in these units of heredity.

In 1865 Gregor Mendel, a monk in an Austrian Roman Catholic monastery, wrote a paper that laid the foundation for modern genetics. Mendel was the first to demonstrate experimentally the manner in which specific traits are passed on from one generation to the next. He concluded that “discrete hereditary elements” (not called genes until the 1900s) in the sex cells are responsible for the transmission of traits. Mendel was ahead of his time, however. The significance of his work was not realized until 1900.

Mendel’s Contributions to Genetics

Pea, a climbing pod-bearing plant (Pisum sativum), or its seed.

In the monastery garden where he conducted his experiments, Mendel observed the inheritance of traits in the easily available garden pea, Pisum sativum. The plant is an ideal genetic working material because a number of progeny can be produced in a short time and because its reproductive parts are so constructed that accidental fertilization is nearly impossible.

Mendel began by tracing the inheritance of one or two contrasting traits at a time. Thus, he crossed tall peas with short peas or red-flowered peas with white-flowered peas. Then he recorded how many of the progeny developed each of the contrasting traits. He used the progeny in subsequent matings to follow the progress of the traits under study through a number of generations.

Somatic cells (or body cells), cells of the body that compose the tissues, organs, and parts of that individual other than the germ cells.

Gamete (or germ cell), sex cell that fuses with a cell of the opposite sex to form new life.

From the evidence obtained in this way, Mendel reasoned that contrasting traits are governed by units of inheritance existing in pairs in somatic, or body, cells but singly in gametes, or sex cells. If the genotype R stands for red and the genotype r for white, then homozygous red-flowered peas have RR somatic cells and R gametes. The somatic cells and gametes of homozygous white-flowered peas are, by contrast, rr and r, respectively.

Allele, in genetics; an alternate form of gene located on a specific site on a chromosome.

The separation of alleles (R from r, for example) in gamete formation is called the principle of segregation. Mendel correctly assumed that chance determines which gene of a pair finds its way into a given gamete. A red-flowered pea may be a heterozygous, or hybrid, Rr. That is, in some way the allele for red flowers (R) “dominates” the allele for white flowers (r). However, the R and r alleles of the hybrid segregate during sex-cell division to produce an equal number of R and r gametes. This is proved by test crossing the hybrid with a homozygous white (rr) plant. Since the homozygous white produces only r gametes and the hybrid produces both R and r gametes, the ratio of red plants to white plants is one to one.

Mendel also demonstrated that non allelic genes (for tall or short and red or white phenotypes, for example) segregate independently of one another into the gametes. This phenomenon is called the principle of independent assortment. For example, a cross between pure strains of tall plants with red flowers (TTRR) and short plants with white flowers (ttrr) produces hybrid progeny that are all tall with red flowers (TtRr). A test cross between these tall, red hybrids (TtRr) and short, white pure strains (ttrr) results in four equally distributed types of progeny 25 percent tall, red TtRr, 25 percent short, red ttRr, 25 percent tall, white Ttrr, and 25 percent short, white ttrr. Modern geneticists have learned, however, that independent assortment does not always hold true because non alleles located side by side on the same chromosome tend to be inherited as a package.

1953: Discovery of DNA structure. The full name of DNA is deoxyribonucleic acid. It carries the codes of genetic information that transmit inherited characteristics to successive generations of living things.

DNA was discovered in 1869 by Friedrich Miescher. In 1943 its role in inheritance was demonstrated. In 1953 its structure was determined by an American biochemist, James D. Watson, and an English physicist, Francis H.C. Crick. Watson and Crick showed the structure to be two strands of a phosphoryl-deoxyribose polymer arranged as a double helix. Watson and Crick were awarded the Nobel prize in physiology or medicine in 1962.

1973: Biotechnology. Two American biochemists, Stanley H. Cohen and Herbert W. Boyer, inaugurated the science of genetic engineering and its associated field of biotechnology in 1973. They showed that it was possible to break down DNA into fragments and combine them into new genes, which could in turn be placed in living cells. There they would reproduce each time a cell divided into two parts.

Genetic engineering makes it possible to modify existing organisms or create organisms that already exist in the human body but that are difficult to isolate. For example, one early product was a genetically engineered form of insulin, used in the treatment of diabetes. Other genetically engineered products include interferons, which are used in the treatment of viral infections and showed promise in the treatment of various forms of cancer. Scientists hope that genetically engineered products will someday prevent or cure such genetic disorders as muscular dystrophy and cystic fibrosis.

Genetic engineering also opens the possibility of creating entirely new organisms. In 1980 the United States Supreme Court ruled that newly developed organisms could be patented, thus giving ownership rights to the companies that made them.

Posted 2012/04/19 by Stelios in Education

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GENETICS (Part 3 of 3)   Leave a comment

Sex Linkage

Linked genes occur on the sex chromosomes as well as on the non sex chromosomes, or autosomes. In humans, a woman carries two X chromosomes and 44 autosomes in each body cell and one X chromosome and 22 autosomes in each egg. A man carries one X and one Y chromosome and 44 autosomes in each body cell and either an X or a Y chromosome and 22 autosomes in each sperm cell.

Only sons inherit traits carried by genes located on the Y chromosome, because a boy (XY) develops whenever a Y sperm fertilizes an egg. Traits carried on genes located on an X chromosome of the father are transmitted only to daughters (XX).

GENES AND THE GENETIC CODE

Genes, the arbiters of body form and organ function, work with precision. They transmit to each cell a genetic code that determines the cell’s purpose.

Nucleic Acids The Key to Heredity

Nucleic acid, any of substances comprising genetic material of living cells; divided into two classes: RNA (ribonucleic acid) and DNA (deoxyribonucleic acid); directs protein synthesis and is vehicle for transmission of genetic information from parent to offspring.

The structure of DNA makes gene transmission possible. Since genes are segments of DNA, DNA must be able to make exact copies of itself to enable the next generation of cells to receive the same genes.

Adenine, a purine base that codes hereditary information in the genetic code in DNA and RNA.

Cytosine, pyrimidine base that codes genetic information in DNA or RNA.

The DNA molecule looks like a twisted ladder. Each “side” is a chain of alternating phosphate and deoxyribose sugar molecules. The “steps” are formed by bonded pairs of purine-pyrimidine bases. DNA contains four such bases the purines adenine (A) and guanine (G) and the pyrimidines cytosine (C) and thymine (T).

The RNA molecule, markedly similar to DNA, usually consists of a single chain. The RNA chain contains ribose sugars instead of deoxyribose. In RNA, the pyrimidine uracil (U) replaces the thymine of DNA.

DNA and RNA are made up of basic units called nucleotides. In DNA, each of these is composed of a phosphate, a deoxyribose sugar, and either A, T, G, or C. RNA nucleotides consist of a phosphate, a ribose sugar, and either A, U, G, or C.

Nucleotide chains in DNA wind around one another to form a complete twist, or gyre, every ten nucleotides along the molecule. The two chains are held fast by hydrogen bonds linking A to T and C to G A always pairs with T (or with U in RNA); C always pairs with G. Sequences of the paired bases are the foundation of the genetic code. Thus, a portion of a double-stranded DNA molecule might read: A-T C-G G-C T-A G-C C-G A-T. When “unzipped,” the left strand would read: ACGTGCA; the right strand: TGCACGT.

DNA is the “master molecule” of the cell. It directs the synthesis of RNA. When RNA is being transcribed, or copied, from an unzipped segment of DNA, RNA nucleotides temporarily pair their bases with those of the DNA strand. In the preceding example, the left hand portion of DNA would transcribe a strand of RNA with the base sequence: UGCACGU.

Genes and Protein Synthesis

A genetic code guides the assembly of proteins. The code ensures that each protein is built from the proper sequence of amino acids.

Genes transmit their protein-building instructions by transcribing a special type of RNA called messenger RNA (mRNA). This leaves the cell nucleus and moves to structures in the cytoplasm called ribosomes, where protein synthesis takes place.

Cell biologists believe that DNA also builds a type of RNA called transfer RNA (tRNA), which floats freely through the cell cytoplasm. Each tRNA molecule links with a specific amino acid. When needed for protein synthesis, the amino acids are borne by tRNA to a ribosome.

For years biologists wondered how amino acids were guided to fit together in the exact sequences needed to produce the thousands of kinds of proteins required to sustain life. The answer seems to lie in the way the four genetic “code letters” A, T, C, and G are arranged along the DNA molecule.

The Genetic Code

Experimental evidence indicates that the genetic code is a “triplet” code; that is, each series of three nucleotides along the DNA molecule orders where a particular amino acid should be placed in a growing protein molecule. Three-nucleotide units on an mRNA strand for example UUU, UUG, and GUU are called codons. The codons, transcribed from DNA, are strung out in a sequence to form mRNA.

According to the triplet theory, tRNA contains anti codons, nucleotide triplets that pair their bases with mRNA codons. Thus, AAA is the anti codon for UUU. When a codon specifies a particular amino acid during protein synthesis, the tRNA molecule with the anti codon delivers the needed amino acid to the bonding site on the ribosome.

The genetic code consists of 64 codons. However, since these codons order only some 20 amino acids, most, if not all, of the amino acids can be ordered by more than one of them. For example, the mRNA codons UGU and UGC both order cysteine. Because mRNA is a reverse copy of DNA the genetic code for cysteine is ACA or ACG. Some codons may act only to signal a halt to protein synthesis.

To illustrate the operation of the genetic code, assume that one protein is responsible for the development of brown hair and that this protein is composed of three amino acid molecules arranged in linear sequence for example, cysteine-cysteine-cysteine. (This is a much simplified example, since proteins actually incorporate from 100 to 300 amino acid molecules.) The gene (DNA segment) specifying formation of this protein reads: ACAACAACA. It produces the mRNA segment UGUUGUUGU. This segment then drifts to a ribosome. Three tRNA molecules, each with the cysteine-bearing anti codon ACA, line up in order on the ribosome and deposit their cysteine to make the brown-hair protein.

Since code transmission from DNA to mRNA is extremely precise, any error in the code affects protein synthesis. If the error is serious enough, it eventually affects some body trait or feature.

Mutations

Down’s syndrome (or mongolism), a congenital condition with moderate to severe mental retardation; characteristic features include: broad flat faces, slanted eyes, small ears and noses; heart defects and other abnormalities.

Certain chemicals and types of radiation can cause mutations changes in the structure of genes or chromosomes. The simplest type of mutation is a change in the DNA or RNA nucleotide sequence. Mutations may also involve the number of chromosomes or the gain, loss, or rearrangement of chromosome segments. If a mutation occurs in parental sex cells, the change is passed on to the offspring. In humans, an extra chromosome in body cells (47 instead of 46) has been implicated in Down’s syndrome, a serious mental abnormality.

Most mutations are considered harmful and are, therefore, eventually eliminated. Some, however, enable an organism to adapt to a changing environment. Biologists believe that mutations have caused the many genetic changes involved in the evolution of species.

Assisted by Val W. Woodward

Genetic Terms

allele. One of the members of a gene pair, each of which is found on chromosomes; the pair of alleles determines a specific trait.

chromosome. A structure in the cell nucleus containing genes.

dominance. The expression of one member of an allelic pair at the expense of the other in the phenotypes of heterozygotes.

gene. One of the chromosomal units that transmit specific hereditary traits; a segment of the self-reproducing molecule, deoxyribonucleic acid.

genotype. The genetic make-up of an organism, which may include genes for the traits that do not show up in the phenotype.

heterozygous. Containing dissimilar alleles.

homozygous. Containing a pair of identical alleles.

phenotype. The visible characteristics of an organism (for example, height and colouration).

recessiveness. The masking of one member of an allelic pair by the other in the phenotypes of heterozygotes.

Posted 2012/04/19 by Stelios in Education

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HUMAN DISEASES (Part 2 of 7)   Leave a comment

What Happens When Immunity Backfires

Paradoxically, a person’s immunity system can backfire and develop auto-antibodies against his own body tissue. In many diseases of unknown cause, doctors have found many unusual antibodies in the blood serum of patients.

Rheumatoid arthritis (RA), chronic disease of the connective tissue, causing painful sensations in joints and muscles.

Doctors think the patients become sensitive to something made by their own bodies. Only a slight change in certain proteins in normal body tissue is necessary for them to become antigens. Most diseases marked by the production of auto-antibodies cannot be traced to infection or drug allergy. In rheumatoid arthritis, for example, the rheumatoid factor is the presence of auto-antibodies in the victim’s blood. These auto-antibodies may stick to the membranes lining the bone joints and cause a reaction that destroys tissue in the joints. In other disorders associated with reversed immunity, auto-antibodies strike red blood cells, tissues surrounding small blood vessels, or other target areas. Ulcerative colitis, a disorder marked by an inflamed portion of the intestine, often with ulcers, is also believed to be an autoimmune disease.

In some cases, lymphocyte defects or discrepancies in antibody production lead to an immune deficiency. The victim is then helpless against recurring infections. A simple head cold can soon become pneumonia. Antibiotics or serums with antibody-rich gamma globulin offer temporary relief in such cases.

1796: Inoculation against disease. The simple medical procedure known as vaccination first came into use in about 1713 as a means of preventing smallpox. Such inoculation sometimes proved dangerous, because individuals sometimes caught a severe case of the disease instead of a mild one. This problem was solved by Edward Jenner, a British physician, in 1796. He realized that individuals inoculated with the much milder cowpox virus became immune to smallpox. Jenner tested his theory in May 1796.

This kind of inoculation earned the name vaccine, from the Latin word vaccinus, meaning “from cows.” Since Jenner’s day vaccines have been developed to fight polio, diphtheria, whooping cough, measles, typhoid fever, cholera, tetanus, and other diseases.

1928: Penicillin. In 1928 the Scottish bacteriologist Alexander Fleming was doing research on the Staphyloccus bacteria when he noticed that a growth of mould Penicillium notatium was contaminating the culture. There was no bacteria where the mould was present. Following up on this fact, Fleming found there was something in the mould that prevented bacterial growth. He named this substance penicillin.

By continued experiment Fleming learned that penicillin is capable of killing many common disease-causing bacteria. His discovery proved to be one of the first and most useful antibiotics used in medicine today. By 1940 penicillin had been turned into an injectable medicine. Its use grew dramatically during World War II as an infection-preventing agent.

HOW DRUGS FIGHT DISEASE

With the advent of drug therapy in the 20th century, doctors began to use lifesaving drugs to fight disease. The clinical use of sulphanilamide, the predecessor of sulphur drugs, in the 1930s and the mass production of penicillin, the first antibiotic, in the 1940s gave physicians extremely powerful tools with which to fight infection. A disease-fighting drug never acts by itself. It always works in conjunction with the body’s immunity system. Vaccines have also become available for the prevention of certain diseases.

How Certain Drugs Quell Infection

Such antibiotics as penicillin, streptomycin, and tetracycline are very effective against bacterial infections. The name “antibiotic” comes from antibiosis, or the use of substances made by one living thing to kill another. Antibiotics are made by bacteria and moulds that are specially cultured in commercial drug laboratories.

Antibiotics kill bacteria and other disease organisms in various ways. Some destroy the cell walls of bacteria. Others interfere with bacterial multiplication or fatally alter the way bacteria make vital proteins. Still others mix up the genetic blueprints of the bacteria.

Ordinarily, an antibiotic tricks bacteria into using the antibiotic’s chemicals instead of closely related ones that the organisms really need for making the key enzymes required for their growth and reproduction. With the antibiotic assimilated into their systems instead of the vital chemicals, an essential activity or structure of the pathogens is lacking and they die.

Sulphur drugs act in a somewhat similar but less effective way. Weakened but not killed by the sulphur drugs, the pathogens fall easy prey to the body’s scavenger cells. Drugs are also available against parasitic worms, infectious amoeba, and other pathogenic organisms.

Antibiotics are not very effective against viruses because the drugs cannot get into the body cells where viruses hide and multiply. However, the body produces a protein called interferon that inhibits viral reproduction.

A drug is sometimes recognized by the body’s immunity system as an antigen. It then triggers a severe reaction. In some cases, a person can suffer anaphylaxis, or extreme sensitivity, to penicillin after repeated injections. Without quick medical aid, severe cases of anaphylactic shock can be fatal.

How Bacteria Become Drug Resistant

Once in every several hundred million cell divisions a mutation makes a bacterium immune to an antibiotic drug. The mutation alters the bacterium’s genetic code and thus its ability to use certain chemicals for its life activities. Mutations can be caused by the radiations from outer space that stream into the Earth’s atmosphere, as well as by some atmospheric chemicals. As a result of the mutation, all bacteria that stem from the immune germ will be resistant to the drug unless any of them undergoes a mutation that makes the strain susceptible again. Hence, whenever a new antibiotic is developed, there will be a chance that bacteria will develop an immunity against it. But because mutations are fairly rare, doctors have a good chance of fighting a bacterial disease with the new drug before future strains become resistant.

Some members of a bacterial strain are resistant to certain drugs naturally. In the course of time they can eventually become selected through evolutionary forces to become the dominant drug-resistant forms of a pathogenic strain.

More importantly, some bacteria can pass on their drug resistance to bacteria of another strain by “infection.” Since the passing of resistance factors does not depend upon the lengthy process of mutation, it poses a much greater problem of drug immunity. As a consequence, doctors often must prescribe more than one antibiotic to fight certain diseases in the hope that this will slow bacterial resistance.

Use of Vaccines and Hormones

A person can become artificially immune to some diseases by means of a vaccine. Vaccines contain antigens that stimulate the production of protective antibodies. Immunity to smallpox, polio, measles, rabies, and certain other diseases, is induced by injecting a person with vaccines containing living but attenuated, or weakened, disease organisms.

A vaccine containing only dead organisms protects against typhoid fever and whooping cough, as well as against measles and polio. Vaccines containing toxins, or poisons, are used to prevent diphtheria and tetanus. When injected into a person, they trigger the production of special antibodies called antitoxins.

Some body disorders are caused by too much or too little hormone production. Hormones are body chemicals that influence many vital biochemical reactions. When someone suffers a hormone deficiency, a doctor usually can treat the deficiency with hormone shots.

1347: Black Death. The plague is one of the most devastating diseases that has ever afflicted mankind. It is a highly contagious fever caused by the bacillus Yersinia pestis, which is carried by fleas that infest rats.

The plague, commonly called bubonic plague or the Black Death, has been known since ancient times, but the best documented instance was its deadly appearance in Europe in 1347. It raged throughout all of Europe, killing at least one-fourth of the population probably 25 million people. Without understanding how it is spread, people had no defence against the disease. Poor sanitary conditions and the disruption of war only worsened the epidemic.

In Europe the epidemic started in Sicily and was spread by shipboard rats to other Mediterranean ports. It moved to North Africa, Italy, Spain, England, and France. By 1349 it made its way to Austria, Germany, Switzerland, and the Low Countries. By 1350 it reached Scandinavia and the Baltic states.

In general, the population of Europe did not recover to its size before the plague until the 16th century, and some towns never recovered. The immediate results of the plague a general collapse of economies, a breakdown of class relationships, and a halt to wartime hostilities forced a massive restructuring of society. It has had a lasting impact on art, literature, and religious thought.

INFECTIOUS DISEASES

Infectious diseases can be transmitted in many ways. They can be spread in droplets through the air when infected persons sneeze or cough. Whoever inhales the droplets can then become infected. Some diseases can be passed through contaminated eating or drinking utensils. Some can be spread through sexual activity. Others can even be spread in the course of medical or surgical treatment, or through the use of dirty injection equipment, especially by drug abusers.

Cold (also called common cold, or coryza), illness, acute inflammation of upper respiratory tract.

Once an infectious organism gains a foothold in the body, it begins to thrive and multiply. Its success is slow or fast, depending upon the nature of the pathogen. The symptoms of the common cold, for example, appear within a few days of infection. However, the symptoms of kuru, an uncommon disease of the nervous system, often appear three years or longer after infection.

Incubation period, length of time before the symptoms of a disease appear.

Every infectious disease has an incubation period. This is the length of time between the pathogen’s gaining a foothold in the body and the appearance of the first symptoms of the disease.

Several factors also determine whether a person will become the victim of a disease after being infected. The number of invading germs the dose of the infection influences the outbreak of disease. So does the virulence of the pathogens; that is, their power to do harm. In addition, the condition of the body’s immunological defences also affects the probability of catching a disease.

Contagious Disease

A great many infectious diseases are contagious; that is, they can easily be passed between people. To acquire certain contagious diseases someone need only be in the presence of someone with it, or come in contact with an infected part of the body, or eat or drink from contaminated utensils.

Someone can be a carrier of a contagious disease in several ways. He can be an asymptomatic carrier, or have a disease without ever developing its symptoms. He can be an incubationary carrier and pass on the pathogens at any time during the “silent” incubation period. He can be a convalescent carrier and transmit some of the infectious organisms remaining in the body even after recovery. Of course, anyone suffering the frank symptoms of a contagious disease can pass it on to others while the disease is running its course.

HEART AND BLOOD SYSTEM DISEASES

Disease of the heart or of the blood vessels, called cardiovascular disease, is the leading cause of death in the United States and Canada. It claims more than a million lives each year in the United States; more than 70,000 each year in Canada.

The heart is a muscular pump. When its own tissue or blood vessels become diseased, serious and sometimes fatal harm can follow.

Coronary Artery Disease

Disease of the coronary arteries that supply oxygen and nutrients to the heart is the most common heart ailment. Coronary artery disease accounts for more than a third of all deaths among males in the United States between the ages of 35 and 55. It also strikes many women past the age of 50. Hypertension (high blood pressure), overweight, cigarette smoking, diabetes mellitus, excess cholesterol, triglycerides and other fats in the blood, and probably lack of regular exercise contribute to the chance of getting coronary artery disease.

Coronary artery disease is characterized by an atheroma, a fatty deposit of cholesterol beneath the inner lining of the artery. The atheroma obstructs the passage of blood, thereby reducing the flow of nourishing blood to the heart muscle. It also sets up conditions for a blood clot in the coronary artery. Atheroma formation seems to run in families. Eating foods rich in saturated animal fat and cholesterol is also thought to contribute to atheroma formation.

Many persons with coronary artery disease do not experience symptoms. If the obstruction is bad enough, however, it may cause angina pectoris, myocardial infarction, or heart enlargement and failure.

Angina pectoris, brief paroxysm of severe chest pain with feeling of suffocation.

Angina pectoris is a chest pain that feels like something is squeezing or pressing the chest during periods of physical exertion. It takes place when the heart’s oxygen needs cannot be met because of a blocked coronary artery. Rest will relieve the pain. Some persons have angina pectoris for years and still live active lives.

Myocardial infarction is commonly called heart attack. Tissue death that results from a lack of blood is called infarction. When the coronary artery becomes so obstructed that the myocardium, or heart muscle, does not receive oxygen, it dies.

Heart attack (also called myocardial infarction, or coronary occlusion), an acute episode of heart disease.

Once, it was believed that a blood clot occluded the coronary artery and caused the infarction. This is why a heart attack is sometimes called a coronary occlusion. However, it now appears that most clots form in the artery after the infarction.

The first few hours after a heart attack are the most critical because abnormal heart rhythms may develop. Ventricular fibrillation is the most dangerous. The ventricles of the heart contract so fast that the pumping action is baulked Death follows in three or four minutes. Heart attack patients are usually treated in the coronary care unit of a hospital for a few days to enable electronic monitoring of the heart rate and rhythm.

Heart failure, condition that develops when repeated heart attacks occur.

Heart failure can occur when repeated heart attacks put too much strain on the remaining healthy heart muscle. As attacks destroy more and more heart muscle, the remaining muscle hypertrophies, or enlarges, to maintain effective pumping. Pressure builds up in a weakened heart, however, and causes fluid backup in the lungs. As a result, the heart output cannot keep pace with the body’s oxygen demands.

PROTECTIVE COLOURATION   Leave a comment

 

Monarch butterfly

DEFINITION: (or colouring) natural colouration of certain organisms allowing them to blend in with their normal environment and escape detection by enemies.

As animals evolved, most of them developed body colours and markings that improved their chances of surviving. This adaptive mechanism, known as protective colouration, may serve any number of functions. Colouring can help protect an animal by making it hard to see. For an animal that spends much of its life trying to avoid dangerous enemies, this is the most useful function. Thus protective colouration is often found among the most helpless creatures those who have little or no other means of defence A white snow hare, for example, blends into its white surroundings and so becomes less visible to predators.

Conversely, colour can help an organism by making it more conspicuous the bright colours of a poisonous snake may warn off intruders, for example. In general, the purpose of protective colouration is to decrease an organism’s visibility or to alter its appearance to other organisms. Sometimes several forms of protective colouration are superimposed on one animal.

Types of Protective Colouration

There are a variety of protective colouration schemes. Each works in a slightly different manner.

Cryptic colouration helps disguise an animal so that it is less visible to predators or prey. One of the most common types of cryptic colouration is background matching, which may take various forms. Many helpless animals have developed colours and markings that match their surroundings in order to hide from predators. Fish eggs and microscopic zoo plankton, for example, are transparent and nearly invisible as they drift in the upper layers of oceans and freshwater lakes. A fawn’s spotted coat camouflages the animal against the speckled forest floor. Some animals attempt to camouflage themselves physically. The decorator crab, for example, cements bits of algae, seaweed, and other ocean debris onto its shell so that it resembles the ocean floor.

Grasshoppers and other insects that live among green plants are often green, and insects that live in the soil, such as ants, are often earth-coloured. The pepper moth has coloured patches that camouflage it against the tree on which it lives. The Sargasso sea dragon lives amid masses of floating algae. The fish is not only coloured to match the plants, but its fins and scales are even shaped like algae. The oriental leaf butterfly, which lives on leaf-littered forest floors, is so intricately and completely camouflaged that its markings include leaf veins and a stem.

Sometimes it is the predator that is camouflaged. Certain predatory fish, for example, blend in with harmless schooling fish and then prey on members of the school. Some species of groupers are camouflaged against the ocean floor as they lie motionless, waiting for prey to swim by.

Certain animals can change their colour in response to different environments or situations. Certain lizards are well known for their ability to match their colour to their surroundings. Varying hares change colours with the season: through the winter their fur is white, and as the snow disappears, their fur turns brown. Thus they remain camouflaged throughout the year.

Another form of cryptic colouration is called disruptive colouration, a scheme in which spots, stripes, or other colour patterns visually break up an animal’s outline. Such patterns may mask the animal’s true shape or make it difficult for a predator to visually resolve it from a colourful or similarly disruptive background. Predators, such as the cheetah, tiger, and leopard, may use their disruptive colouration to avoid being seen. The spots or stripes on their fur allow them to get close to their prey before being observed, improving their chances of getting food. Many fishes and certain birds exhibit disruptive colouration, as do some snakes. The boa constrictor, a tree dweller that grows to several feet in length, is marked with a complex pattern of spots and stripes so complete that a stripe even extends across its eyes. Some patterns of disruptive colouration operate on the same principle to conceal movement. Snakes that are concentrically banded, for example, are difficult to detect when they move between long blades of grass.

A third form of cryptic colouration is counter shading, designed to mask an organism’s three-dimensional form. Many animals, particularly vertebrates, are counter shaded, or shaded lighter on their lower surfaces and darker on their upper surfaces. This colouration counteracts the effects of overhead light, which accentuates an animal’s three-dimensional form by lightening the animal’s upper body and casting its lower body into shadow.

Counter shading gives the body a more uniform darkness and less depth relief so that the animal is less conspicuous.

Many marine animals are counter shaded so that they will not appear as silhouettes when seen from below. A silhouetted organism would be conspicuous and thus attract predators. When viewed from above, counter shaded marine animals blend into the darkness of the sea bottom; when viewed from below, their light lower bodies match the appearance of the water’s surface.

Alluring colouration Some animals are coloured so that a predator’s attention is drawn to a non-vital part of the animal’s body. The lizard known as the blue-tailed skink has a bright blue tail that the animal can shed at will with no harm to itself. Potential predators are attracted to the tail; if they attack the tail, the skink sheds it and darts away unharmed.

Monarch butterfly, insect (Danaus plexippus) of the order Lepidoptera, family Danaidae; breeds on milkweeds.

Warning colouration is intended not to camouflage an organism but to make it more noticeable. Such colouration is found among animals that have natural defences that they use to deter or fend off predators. These defences can take many forms. An animal may simply cause a disagreeable smell (such as a skunk’s odour), or it may actually cause pain (as from bee’s sting) or even death (as from snake’s venom). Many of these animals are brightly coloured, presumably as a warning to potential aggressors. The monarch butterfly, for example which bears a conspicuous pattern of bright orange and black has such a disagreeable taste that a bird will often regurgitate after eating it. Behavioural biologists believe that predatory animals learn to associate such brightly coloured animals with unpleasant or painful experiences and therefore are likely to pass them up as potential prey in favour of a more drab animal. Common warning colours are red, black, and yellow.

Dewlap, in reptile anatomy, a hanging fold of skin under the neck.

Some organisms can change their colour from drab to bright when threatened. The octopus, for example, turns white when agitated and red when it is suddenly frightened. Certain chameleons, usually camouflaged, display a brightly coloured throat sac, or dewlap, as a warning signal to invaders. Furthermore, when a male chameleon enters another’s territory, the dewlap display of the territory’s “owner” serves as a warning to keep out.

Fin, in zoology, external membrane used for propulsion in water.

Other forms of protective colouration Some animals are coloured in such a way that they draw attention to themselves only when they are in motion. Certain birds have light-coloured feathers that are visible only during flight. When the bird comes to rest, these feathers are tucked under darker feathers, so that the bird is once again inconspicuous. Similarly, many fishes have colourful dorsal fins that are extended while the fish is swimming then folded down when the fish is at rest.

In both cases, the animal can use its colouration to perform a sort of disappearing act. It can draw a predator away from a certain area, perhaps a nest of vulnerable offspring, by catching the predator’s attention and moving to another location. If the predator pursues the decoy, the bird or fish can disappear by coming to rest.

Some organisms imitate the protective colouration of others. This phenomenon is known as mimicry. A harmless animal may display the same warning colouration as a dangerous or inedible one in order to deceive predators into reacting as though the benign animal had the same defences as its model. In other cases, several noxious species will share a similar warning colouration so that potential predators will generalize and avoid all species with such colouring

Evolution of Protective Colouration

The intricate schemes of protective colouration are the results of long-term evolution. Through aeons of adaptive changes, certain organisms have acquired patterns of colouration that have helped them survive and reproduce.

Effective forms of protective colouration have been passed on to following generations. The processes of mutation, natural selection, and reproduction have combined to produce many organisms with colourations that are fine-tuned to their individual environments and their individual protective needs.

Assisted by Elliot Mitchell, science teacher, Latin School of Chicago.

MIMICRY – close resemblance, in colour, form, or behaviour, it serves to disguise or conceal the organism from predators   Leave a comment

Helen Zille sounding like an African

A fascinating result of evolution is the phenomenon of mimicry, the superficial resemblance of one organism to another that gives the mimicking organism some advantage or protection from predators. Many plants and animals have evolved such resemblances in order to increase their own chances of survival. A walking stick, for example, is an insect that closely resembles the twig of a plant. By virtue of this similarity, or mimicry, it often remains unnoticed by predators. The chameleon is a tree-dwelling lizard that is able to change its body colour to blend in with a variety of backgrounds.

Monarch butterfly, insect (Danaus plexippus) of the order Lepidoptera, family Danaidae; breeds on milkweeds.

Biologists have distinguished between several types of mimicry. In 1861 the English naturalist Henry Walter Bates described a form of mimicry in which the mimic takes advantage of the defences of its model. Such mimicry is called Batesian mimicry. In a well-known instance, the monarch butterfly serves as the model. The monarch is extremely distasteful to many birds; in fact, a bird that eats the monarch will often vomit shortly after its meal. Consequently many otherwise predatory birds will shun the monarch. The viceroy butterfly, which is not distasteful itself, has assumed colouring and markings very similar to the monarch, and thus many birds will avoid it as well. Another example is the harmless snake caterpillar, which can mimic the body and movement of a snake to discourage its natural predators.

Another style of mimicry was described in 1878 by the German zoologist Fritz Muller. In Mullerian mimicry two similar species derive mutual benefits from their resemblance. For example, two wasps, the sand wasp and the yellow jacket, are very similar in appearance, and both can inflict a painful sting. A predator that encounters either the sand wasp or the yellow jacket will learn to associate their colouration with pain and will thenceforth avoid preying on either species.

Anglerfish, marine fishes of the order Lophiiformes with lure-like appendages for baiting prey.

In yet another form of mimicry, called aggressive mimicry, a predator mimics a harmless organism in order to catch its unwitting prey. One aggressive mimic, the angler fish, lies motionless in the water while waving a small fishlike appendage. When a would-be predator approaches to eat the bait, it becomes a quick meal for the angler fish. Another fish, the sabre-toothed blenny, mimics the colour and behaviour of the harmless cleaner wrasse, which feeds on parasites attached to other fish. The blenny uses this resemblance to get close enough to its prey to attack it before it can recognize the deception.

The European cuckoo exhibits a type of parasitic mimicry. It lays its eggs in the nest of a bird whose eggs are similar in appearance. The host bird then raises the cuckoo’s young.

Mimicry is the product of natural selection. Mimicking organisms have developed their particular similarities over time. Each step of the organism’s transition has given it some slight advantage that has increased its chances for survival. For example, a change in colouration that allows a predator to camouflage itself may increase its chances of sneaking up on its prey. Thus it is able to acquire more food and increase its chances of staying healthy, surviving, and reproducing. Evolutionary biologists have used mimicry as a research tool and to help prove Charles Darwin’s theory of evolution. They can trace the evolution of mimicking organisms to learn how long the model and mimic have shared a habitat and to what selective pressures the two organisms have adapted.

Assisted by Elliot Mitchell.

Posted 2012/01/14 by Stelios in Education

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ANTHROPOLOGY (Part 1 of 2).   Leave a comment

The science that studies human cultures is called anthropology. It is a discipline that deals with the origins and development of human societies and the differences between them. The word anthropology is derived from two Greek words: anthropos meaning “man” or “human”; and logos, meaning “thought” or “reason.” Anthropologists attempt, by investigating the whole range of human development and behaviour, to achieve a total description of cultural and social phenomena.

The Spheres of Anthropology

The science of anthropology is divided into two major disciplines, physical anthropology and cultural anthropology. Each of these is basically an independent science, although specialists in one field frequently consult and cooperate with scholars in the other. Physical anthropology is generally classified as a natural science, while cultural anthropology is considered a social science.

Physical anthropology is concerned with the biological aspects of human beings. In trying to learn about racial differences, human origins, and evolution, the physical anthropologist studies fossil remains and observes the behaviour of other primates. Primates are an order of mammals that includes human beings as well as apes and monkeys.

Cultural anthropology deals primarily with the growth of human societies in the world. It is a study of group behaviour, the origins of religion, social customs and conventions, technical developments, and family relationships. A major sub field of cultural anthropology is linguistics, the study of the history and structure of language. Linguistics is a valuable tool of the anthropologist because it enables him to observe a people’s system of communication and to learn the ideas by which they view the world. It also enables him to collect an oral history of the group being studied. Oral histories are constructed from a society’s poems, songs, myths, proverbs, and folk tales.

Physical and cultural anthropology are connected by two other fields of study: archaeology and applied anthropology. In excavations, archaeologists find the remains of ancient buildings, tools, pottery, and other artefacts by which a past culture may be dated and described.

Applied anthropology makes use of the research done by physical and cultural anthropologists in order to help governments and other institutions form and implement policies for specific population groups. It may, for instance, aid governments of underdeveloped countries in showing backward peoples how to cope with the complexities of 20th-century civilization. It may also be used by governments in the formulation of social, educational, and economic policies for ethnic minorities within their borders. The work of applied anthropology is often done by specialists in the fields of economics, sociology, history, and psychology.

Because anthropology is such a wide-ranging discipline, investigating as it does every facet of all human societies, it must draw upon research done in other disciplines to form its conclusions. Among these disciplines are history, geography, geology, biology, anatomy, genetics, economics, psychology, and sociology, along with the highly specialized tasks of linguistics and archaeology already mentioned.

The Problem of Terminology

Different terms are used to describe the fields of anthropology in the United States and Europe. While in the United States the term anthropology is used to name the whole subject, in Europe the name ethnology is applied. (Ethnology is defined as the science that studies the many races of mankind their beginnings, characteristics, differences, and distribution.) What is called “cultural anthropology” in the United States is also termed “ethnology” in European countries. The term physical anthropology is used in both parts of the world.

The sub areas of cultural anthropology in the United States are three: historical anthropology (or ethnology), prehistory (or prehistoric archaeology), and linguistics (or linguistic anthropology). In Europe the sub areas are: ethnology (in the strictest sense as the historical description and comparison of races), prehistory (or prehistoric ethnology), and linguistics (or linguistic ethnology).

PHYSICAL ANTHROPOLOGY

The science of physical anthropology has focused to a great extent on determining the place of human beings in nature, on comparing them with lower primates, and on interpreting the physical differences among the races. In pursuing its goals, physical anthropology has used the sciences of comparative anatomy, evolution, and genetics.

Early Investigations

Modern physical anthropology began taking shape in the first half of the 19th century when there arose a great interest in studying the origins of mankind, the biological relationships between the races, and the changeability of man as an animal species. In working out their theories, anthropologists devised a framework called the “great chain of being.” This was a model of nature that arranged all species in a hierarchical order, from the lowest to the highest. The point of this notion was to discover if there was steady progression from lower life forms up through the lower primates (apes and monkeys) to human beings. Since no continuous progression to human beings could at first be found, scientists theorized that there must be a “missing link” between the lower primates and man.

In order to classify and distinguish between the apes, monkeys, and races of man, the anthropologists have used comparative anatomy, measuring brain size, cranial capacity, arm and leg length, and height. They have also noted the colour of skin and personality traits as clues for putting animals and races in their proper order.

The work of most 19th-century anthropologists was hampered by ignorance in a number of areas, including an ignorance that has since been dissipated by geology, astronomy, archaeology, and the biological sciences. The age of the Earth was unknown. Many people, in accordance with the religious teachings of the time, believed it to be about 6,000 years old. Religious teaching also suggested that all species were created at one time, thus precluding any evolution from lower to higher forms. The first archaeological discoveries indicating the very ancient origins of mankind were not made until the middle of the 19th century, and then many anthropologists ignored or disputed them. The first major breakthrough for anthropologists came in the natural sciences when in 1859 Charles Darwin published his ‘Origin of Species by Means of Natural Selection’.

Evolution, as first described by Darwin, was a crucial concept for anthropologists in reaching an understanding of the origins of man. The essential impact for the evolution of man was the idea of natural selection, although many decades passed before its implications were appreciated or employed. Darwin showed that nature selects those forms that are better adapted to a particular geographic zone and way of life. The notion of adaptation implied that organisms changed slowly over millions of years. It also disqualified any need for a “missing link,” although this theory persisted well into the 20th century. The missing link had not been considered to be a product of evolutionary development but a creature placed between man and ape in the natural order of things.

Modern Physical Anthropology

A major shift in the approach to physical anthropology occurred at the beginning of the 20th century with the discovery of genetic principles and of the ABO blood groups. Genetics was actually rediscovered. In 1865 an Austrian monk, Gregor J. Mendel, had formulated the first laws of heredity and laid the foundation of the science of genetics. His findings were almost entirely ignored at the time. In 1900 three other European botanists arrived at the same conclusions that Mendel had published 35 years earlier, and in researching the literature on the subject they found his work.

Genes are the units within sex cells such as the sperm and egg that transmit specific hereditary traits from one generation to the next. The study of inherited traits has become essential to anthropologists in seeking to understand human variations and differences between races. Genetics has modified the theory of progressive evolution somewhat, because it has been shown by experiment that there may be genetic reversals that is, reversions back to traits and characteristics thought to be discarded in the hereditary process.

Early in the 20th century another Austrian, a physician named Karl Landsteiner, discovered the blood groups, or types, known as O, A, B, and AB. This led anthropologists to investigate blood differences among the races. They have noted that certain races and sub races have particular distributions of one or another blood type. This has enabled scientists to categorize the races and, since blood types are genetically determined, to trace early migration patterns.

Dating is crucial for physical anthropologists, as well as for geologists and archaeologists. It is a method that allows them to determine how old something is whether it be a layer of rocks, a human-like fossil, or a collection of pottery.

There are two kinds of dating: relative and absolute. Relative dating shows the order in which events occurred but does not tell exactly when they occurred. Methods of absolute dating indicate with a fair degree of precision how old something is. Of the two types of dating, the determination of relative age relationships came into use first. Absolute dating depends upon technological advances that have been made in the 20th century.

Geologists and archaeologists have long used relative dating methods to determine the approximate age of the Earth and of fossils and artefacts Geologists examine the many strata of the Earth’s crust to determine the intervals of time from one layer of rock to another. Archaeologists also use the principle of layering to verify the sequence of human cultures.

Another method of determining relative age is fluorine dating. It is based upon the principle that fossil bones absorb the element fluorine from the soil in which they are buried. The longer they are buried, the more fluorine the bones will contain. Determining the amount of fluorine is often not a practical means of relative dating because it requires many samples from an immediate area.

Absolute dating attempts to pinpoint when a given rock, fossil, or other object reached its present condition. The basic method for determining absolute age is called radiometry measuring the rate of radioactive decay of an element. This can be done with a high degree of accuracy, although no method is infallible without a great deal of corroborative testing.

One of the types of absolute dating that has been used by physical anthropologists is potassium-argon dating. It is a method of determining the time of origin of rocks and thereby of the fossils found within them by measuring the amount of decay of potassium-40, a radioactive isotope of the element potassium, into the element argon, one of the rare gases. The half-life of potassium-40, which is the time it will take one half of any quantity of it to decay into potassium, is 1,265,000,000 years. Potassium-argon dating has been used to measure the ages of a wide variety of objects, from meteorites 4,500,000,000 years old to volcanic rocks only 20,000 years old. Such dating techniques applied to the remains and surroundings of ancient human beings have constantly pushed back the estimated age of mankind. By the early 1980s man was believed to be at least 3 million years old. This is based on the dating of a number of remarkable discoveries of fossil remains made in the Great Rift Valley of Africa, at sites in Ethiopia, Kenya, and Tanzania.

CULTURAL ANTHROPOLOGY

Cultural anthropologists are concerned with the origin and development of human societies in all their complexity. Cultural anthropology attempts to devise theories to explain the origin of aspects of various human cultures, each of which has unique features as well as characteristics in common with other societies.

Within the field of cultural anthropology, several schools of thought have arisen some mutually contradictory since the 19th century. Among them are evolutionism, historical particularism, diffusionism, functionalism, structuralism, and neo-evolutionism.

Evolutionism

The theory of biological evolution was first formally presented by Charles Darwin in ‘On the Origin of Species’ in 1859. This theory argued that man is an animal and possesses many of the same instincts and needs as do other social animals. Darwin stated that successful species adapted to changing environmental conditions, and that through a process he called natural selection only the most adaptable individuals or groups survive.

Lewis Henry Morgan, (1818-81), U.S. archaeologist and ethnologist, born near Aurora, N.Y. (‘League of the Ho-de-no-sau-nee, or Iroquois’; ‘Ancient Society’); bequeathed fund to found women’s college in University of Rochester.

Nineteenth-century anthropologists applied these theories to their cultural studies. They believed that all societies follow a universal sequence in their development, and that all men possess the same thought processes and basic mental structure. In 1855, for example, sociologist Herbert Spencer claimed that all societies develop from simple to more complex groups. According to Lewis H. Morgan of the United States, the three basic stages that all societies must pass through are savagery, barbarism, and civilization. Each of these stages, he believed, is characterized by specific technological developments.

A related 19th-century approach that applied evolution to society focused on stages of religious thought. Sir Edward Tylor, an English anthropologist, argued that these stages are animism, or a belief in the soul and in spirits; polytheism, or a belief in more than one god; and monotheism, or a belief in one god. Tylor also suggested that some groups could skip particular stages in their cultural development by learning from other cultures.

Another kind of cultural evolution was proposed by Karl Marx and Friedrich Engels. This theory defined a society by its method of producing goods and services and presented a developmental sequence that included necessary social conflict.

Cultural evolutionists analysed aspects of modern cultures that seemed to have survived from previous stages. They developed a number of points of view that are considered valuable contributions to anthropology. Among these are the concept of culture itself, the methods of comparing different cultures, and concepts for the study of social organizations.

Two major works in the field of anthropology, Sir James Frazer’s ‘Golden Bough’ (1890) and Ernest Crawley’s ‘Mystic Rose’ (1902), contained vast amounts of research on primitive and traditional societies and tended to reinforce the theories of evolutionists. Both were encyclopaedic collections of customs, religious and magical practices, and much other curious data. Evolutionists saw evidence of a sequence of magical, religious, and scientific thought that seemed to be part of the development of every human society.

Historical Particularism

By the beginning of the 20th century, anthropologists in Great Britain, Germany, and the United States were questioning the belief that all societies developed in much the same way. They suggested that each culture was unique because each had its separate geography, history, creativity, and degree of contact with its neighbours

One of the first to reject evolutionism was a German-born American anthropologist, Franz Boas. Boas emphasized the importance of fieldwork and observation. Fieldwork involves seeking information about a particular group’s behaviour by gathering data and recording observable behaviours in that group’s natural environment.

Boas believed that every aspect of a culture should be recorded and that the anthropologist studying a native culture should not only learn its language but should attempt to think like its people. Boas emphasized the importance of collecting information that described the individuals and their interrelationships in a particular culture. Such information was gathered through the recording of life histories and folklore, and then connecting these details with archaeological and historical data. Boas also believed that similarities among different cultures were the result of similar outside influences rather than to the similarity in thought processes or to any universal laws of development. He stressed the importance of analysing a culture within its historical context.

Boas is known as the founder of the culture history school of anthropology, which dominated American cultural anthropology for much of the 20th century. Anthropologists who followed Boas’ theories included Ruth Benedict, Alfred L. Kroeber, Margaret Mead, and Edward Sapir.

Posted 2011/12/14 by Stelios in Education

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RELIGION.   1 comment

It has been said that thoughts of death lead necessarily to the development of religion. It is difficult to imagine what need there would be for religion in a world in which no one ever died or became ill. All religions attempt to give answers to basic questions: From where did the world come? What is the meaning of human life? Why do people die and what happens afterwards? Why is there evil? How should people behave? In the distant past these questions were answered in terms of mythology. Much of literature deals with them. Modern sciences try to investigate them.

As a word religion is difficult to define, but as a human experience it seems to be universal. The 20th-century German-born American theologian Paul Tillich gave a simple and basic definition of the word: “Religion is ultimate concern.” This means that religion encompasses that to which people are most devoted or that from which they expect to get the most fundamental satisfaction in life. Consequently, religion provides adequate answers to the basic questions posed above.

Four centuries earlier the German reformer Martin Luther spoke in similar terms about God. He stated that to have a god was to “have something in which the heart trusts completely,” whether such a god was a supernatural being or something in the world like wealth, power, career, or pleasure. Putting Tillich’s and Luther’s definitions together, it is possible to see that religion does not necessarily have to be involved with shrines, temples, churches, or synagogues. It does not need complex doctrines or clergy. It can be anything to which people devote themselves that fills their lives with meaning.

In Western civilization religion has traditionally been defined as belief in and worship of one God. This is true for Judaism, Christianity, and Islam. The statements by Tillich and Luther make it clear, however, that such a definition may be too narrow. In original Buddhism in India and Confucianism in China, there was no recognition of a supreme being. Both of these philosophies were basically concerned with patterns of human behaviour

Regardless of definitions, all religions (as the word is normally used) have certain elements in common. These include common rituals to perform, prayers to recite, places to frequent or avoid, holy days to keep, means by which to predict the future, a body of literature to read and study, truths to affirm, charismatic leaders to follow, and ordinances to obey. Many have buildings set aside for worship, and there are activities such as prayer, sacrifice, contemplation, and perhaps magic.

Closely associated with these elements is personal conduct. Although it is possible to separate ritual observances from moral conduct, worship has normally implied a type of relationship with a god from which certain behaviour patterns are expected to follow. A notable exception in history is the official state religion of ancient Rome, which was kept separate from personal commitment and morality.

Religion and Belief

The existence of religion is rooted fundamentally in human ignorance. People do not know the origin of the world, why there is death, or the answers to other basic questions. Explanations must be devised on the basis of a complete lack of evidence. The first explanations gave the world the fascinating mythologies of the ancient Greeks, Romans, and other civilizations. Under the influences of Judaism and Christianity, mythology was replaced in Western civilization by religions based on historical events. Nevertheless, all acceptance of religion is based on belief, not on the weight of evidence or the reaching of reasonable conclusions.

Atheism, the belief that there is no Supreme Being or God; usually associated with materialism (the belief that matter is the sole guiding force of the universe); the term comes from the Greek word atheos, meaning “without God”.

This means, for example, that all statements about God or the gods are statements of belief. Even the assertion that there is no God atheism is a statement of belief. In the case of religions based on historical events, interpretations of those events are accepted by believers as true. Non-believers arrive at completely different interpretations.

If belief is the key to religion, it is also the chief problem. If religion were a form of knowledge, then its teachings would have to be supported by visible evidence that could be examined by everyone. There would then be widespread acceptance of it as knowledge as there is in mathematics or the natural sciences. But there can be no evidence, as science understands the term, that a supreme being created the universe. Nor can there be any evidence of life after death. These and other beliefs are not open to verification; they are matters of faith. One trusts that they are true, and they seem to give valid explanations to fundamental questions.

Religion and Science

Modern science had its origins in the late Middle Ages, especially during the period called the Renaissance. Many of its discoveries brought it into conflict with the traditional beliefs held by the medieval church. The assertion by Galileo and others that the Earth was not the centre of the universe outraged many church leaders, and Galileo was brought to trial for teaching unacceptable doctrines.

Conflicts between religion and science did not cease with the Renaissance. Today there are many religious people who condemn all teaching about the theory of evolution. They assert that the Biblical account of creation is literally true; therefore, evolution is unacceptable to them.

Opposition between religion and science arose from the mistaken notion that religion could present its doctrines as undisputed knowledge that would hold true for all time. The medieval church had incorporated into its system of belief certain ancient scientific assertions about the Earth and the heavens. As these assertions were slowly proved false, the church reacted because it had used ancient science to support its doctrine. In other words, it had attempted to use assumed facts of science to support belief. It feared, consequently, that if the facts were swept away, the belief would crumble. As it happened, religious resistance to science alienated many educated people.

The church did not realize that real belief cannot be supported by evidence from science. Nor can belief be undone by scientific evidence. The sciences deal with what they can see, inspect, and experiment with. They can make no valid statements about the existence or non-existence of a god because such statements must be made without any available evidence. On the other hand, religion cannot pretend to invalidate the findings of scientists for fear that belief will be challenged. If the objects of faith are true and the objects of scientific discovery true as well, then the objects are equally true and cannot contradict each other.

The uneasiness between science and religion has not been limited to Christianity. Marxist communism of the 20th century has become a kind of religion. It has an all-embracing world-view, and it has a faith in the historical process for which no evidence exists. During Joseph Stalin’s rule in the Soviet Union, scientific theories that seemed to contradict his version of Marxism were suppressed. Stalin’s favourite scientist was Trofim Lysenko, a biologist and agronomist who supported theories on heredity completely at variance with the genetic principles developed by Gregor Mendel. Through Lysenko’s influence and under Stalin’s insistence, all other approaches to biology were outlawed. Some scientists who had previously taught Mendelian genetics were forced to change their opinion and teach Lysenko’s version of biology.

Posted 2011/12/04 by Stelios in Education

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