To contact us:

Phone: +2348063832484








The two lobes of a Venus’s-flytrap leaf form a deceptively safe and attractive landing place for insects and other animals. Less than a second after the frog trips the trigger, bristles on the inside surface of the leaf, the lobes close enough to trap the intruder below interlocking spines. If sensory organs determine that the prisoner contains protein, the leaf closes further, and the plant’s digestive enzymes start to flow.

Oxford Scientific Films

Biodiversity or Biological Diversity, sum of all the different species of animals, plants, fungi, and microbial organisms living on Earth and the variety of habitats in which they live. Scientists estimate that upwards of 10 million—and some suggest more than 100 million—different species inhabit the Earth. Each species is adapted to its unique niche in the environment, from the peaks of mountains to the depths of deep-sea hydrothermal vents, and from polar ice caps to tropical rain forests.

Bacterium Showing Flagella

Although many forms of bacteria are not capable of independent movement, species such as the Salmonella bacterium pictured here can move by means of fine threadlike projections called flagella. The arrangement of flagella across the surface of the bacterium differs from species to species; they can be present at the ends of the bacterium or all across the body surface. Forward movement is accomplished either by a tumbling motion or in a forward manner without tumbling.

Chris Bjornberg/Science Source/Photo Researchers, Inc.

Biodiversity underlies everything from food production to medical research. Humans the world over use at least 40,000 species of plants and animals on a daily basis. Many people around the world still depend on wild species for some or all of their food, shelter, and clothing. All of our domesticated plants and animals came from wild-living ancestral species. Close to 40 percent of the pharmaceuticals used in the United States are either based on or synthesized from natural compounds found in plants, animals, or microorganisms.

Scarlet Ibis

The scarlet ibis is one of 30 species of wading birds characterized by a long neck and legs. It has bright red plumage and dwells in the marshes, lakes, and shallow coastal waters of Venezuela and Brazil.

Roland Seitre/Peter Arnold, Inc.

The array of living organisms found in a particular environment together with the physical and environmental factors that affect them is called an ecosystem. Healthy ecosystems are vital to life: They regulate many of the chemical and climatic systems that make available clean air and water and plentiful oxygen. Forests, for example, regulate the amount of carbon dioxide in the air, produce oxygen as a byproduct of photosynthesis (the process by which plants convert energy from sunlight into carbohydrate energy), and control rainfall and soil erosion. Ecosystems, in turn, depend on the continued health and vitality of the individual organisms that compose them. Removing just one species from an ecosystem can prevent the ecosystem from operating optimally.


Although many starfish have 5 arms, or rays, some species may have as many as 44 arms. All starfish can grow back arms lost through predation and physical injury. Starfish have a flattened body with the mouth located on the oral, or lower body surface. Many starfish can evert their stomach through their mouth to feed on food items too large to ingest.

Dorling Kindersley

Perhaps the greatest value of biodiversity is yet unknown. Scientists have discovered and named only 1.75 million species—less than 20 percent of those estimated to exist. And of those identified, only a fraction have been examined for potential medicinal, agricultural, or industrial value. Much of the Earth’s great biodiversity is rapidly disappearing, even before we know what is missing. Most biologists agree that life on Earth is now faced with the most severe extinction episode since the event that drove the dinosaurs to extinction 65 million years ago. Species of plants, animals, fungi, and microscopic organisms such as bacteria are being lost at alarming rates—so many, in fact, that biologists estimate that three species go extinct every hour. Scientists around the world are cataloging and studying global biodiversity in hopes that they might better understand it, or at least slow the rate of loss.




Everywhere there is life, there is more than one distinct type of organism. Even a drop of seawater offers a multitude of different microscopic plants, animals, and less complex life forms. The rich diversity of the living world is connected in two distinct ways. First, different types of organisms live side by side in complex ecological networks of interdependency, each relying on the others that share its habitat for nutrients and energy. Second, all life on Earth is connected in an evolutionary tree of life. At the bottom of the tree is the common ancestor from which all living things descended—a single-celled microbe that lived more than 3.5 billion years ago—and in its uppermost branches are gorillas, chimpanzees, orangutans, and our own species, Homo sapiens.



Ecological Diversity

Sea Otter Floating and Eating

Native to the American and Asian shores of the North Pacific Ocean, sea otters feed and nurse while floating on their backs. Sea otters help maintain diversity in subtidal waters because they feed on sea urchins, which would otherwise graze kelp forests to extinction.

BBC Worldwide Americas, Inc.

Ecological diversity is the intricate network of different species present in local ecosystems and the dynamic interplay between them. An ecosystem consists of organisms from many different species living together in a region that are connected by the flow of energy, nutrients, and matter that occurs as the organisms of different species interact with one another. The ultimate source of energy in nearly all ecosystems is the Sun. The Sun’s radiant energy is converted to chemical energy by plants. This energy flows through the systems when animals eat the plants and then are eaten, in turn, by other animals. Fungi derive energy by decomposing organisms, releasing nutrients back into the soil as they do so. An ecosystem, then, is a collection of living components—microbes, plants, animals, and fungi—and nonliving components—climate and chemicals—that are connected by energy flow.

Removing just one species from an ecosystem damages the flow of energy of that system. For instance, in the late 19th and early 20th centuries, sea otters were hunted to near extinction in many kelp forests off the coast of the Pacific Northwest of the United States and western Canada, causing the entire ecosystem to suffer. Otters eat sea urchins, small, spiny organisms that share their habitat. When the otters disappeared, the sea urchin population exploded and started to destroy the vast beds of kelp. Without the kelp, other species that lived in the ecosystem, including many species of fish and snails and other invertebrates, began to decline in number. Efforts to restore sea otter populations brought the kelp communities back to near normal in the late 20th century.

Blue Spotted Sea Urchin

This underside view of the blue spotted sea urchin shows its mouth apparatus, commonly called Aristotle’s lantern. This structure is composed of five jaws arranged in a radial, or concentric, pattern. This arrangement allows the sea urchin to feed efficiently on a variety of marine algae and kelps. When sea otters were hunted to near extinction on the Pacific coast of North America, sea urchin populations exploded. In the absence of their primary predator, the urchins overgrazed kelp beds, devastating their entire ecosystems.

Oxford Scientific Films

Measuring ecological diversity is difficult because each of the Earth’s ecosystems merges into the ecosystems around it. A lake, for example, might have a distinct shoreline, but the plants fringing its edges are quite different from the aquatic plants in the middle of the lake or the trees and shrubs surrounding the lake. Beavers may live in the lake, but they construct dams from trees that grow in adjacent ecosystems. Nutrients flow into the lake via streams and rivers beyond the lake’s ecosystem.



Evolutionary Diversity

Animal Kingdom

Kingdom Animalia includes more than one million living species, grouped into more than 30 phyla. Vertebrates, members of the phylum Chordata, comprise only one percent of these organisms. Phylum Arthropoda is more successful in sheer numbers, total mass, and distribution than all other groups of animals combined. The remaining animal phyla are composed of mostly marine-dwelling organisms. Illustrated here is the evolutionary relationship between all of these groups.

Booktionary Corporation. All Rights Reserved.

Every species on Earth is related to every other species in a pattern every bit as complex as the patterns of energy flow within an ecosystem. In evolutionary diversity, the connection is not energy flow, but rather genetic connections that unite species. The more closely related any two species are, the more genetic information they will share, and the more similar they will appear. An ever-widening circle of evolutionary relatedness embraces every species on Earth.

An organism’s closest relatives are members of its own species—that is, other organisms with which it has the potential to mate and produce offspring. Members of a species share genes, the bits of biochemical information that determine, in part, how the animals look, behave, and live. One eastern gray squirrel, for example, shares the vast majority of its genes with other eastern gray squirrels, whether they live in the same area or are separated by thousands of miles. Members of a species also share complex mating behaviors that enable them to recognize each other as potential mates. When a female eastern gray squirrel is ready to mate, she exudes a scent that attracts male eastern gray squirrels. Mating and sharing a common supply of genes unite a species.

For virtually every species there is a similar and closely related species in an adjacent habitat. West of the Rocky Mountains, one finds western gray squirrels instead of eastern gray squirrels. Although western gray squirrels are more similar to than different from their eastern counterparts, these animals do not share a common mating behavior with eastern gray squirrels. Even when brought into close proximity, eastern and western gray squirrels do not mate, and so constitute two distinct species.

Gray Squirrel

Like other tree-dwelling squirrels, the gray squirrel, Sciurus carolinensis, feeds mainly on nuts, seeds, fruits, and other types of plant material. Caching supplies, it may bury an acorn 30 m (100 ft) away from the tree that produced it. The sensitive noses of some squirrels can recover a store hidden more than a foot below the surface. While a forgotten acorn may germinate and grow into a new tree, gray squirrels can harm more than help a tree population. Especially in Great Britain, the gray squirrels’ unexplained habit of stripping the bark from young trees has taken its toll. Even oak trees, in which the species tends to build its bulbous nest, called a drey, are not spared from their gnawing teeth.

Dorling Kindersley

Each species has other, more remotely related species, which share a more general set of characteristics. Gray squirrels, chipmunks, marmots, and prairie dogs all belong to the squirrel family because they share a number of features, such as tooth number and shape, and details of skull and muscle anatomy. All of these animals are rodents, a large group of more distantly related animals who share similar chisel-like incisor teeth that grow continuously. All rodents are related to a broader group, mammals. Mammals have hair, raise their young on milk, and have three bones in the middle ear. All mammals, in turn, are more distantly related to other animals with backbones, or vertebrates. All these organisms are animals but share a common cell structure with plants, fungi, and some microbes. Finally, all living organisms share a common molecule, ribonucleic acid (RNA), and most also have deoxyribonucleic acid (DNA). These molecules direct the production of proteins—molecules responsible for the structure and function of virtually all living cells.









Preliterate Societies

Trepanned Skull

Trepanning, the procedure of cutting a hole in the skull, is the earliest known medical operation. Some anthropologists believe that trepanning was performed on people with mental illnesses to drive out evil spirits from their heads. This skull dates from the Inca civilization.

Daniele Pellegrini/Photo Researchers, Inc.

Evidence for trepanning, the surgical procedure of cutting a hole in the skull, dates back 4,000 to 5,000 years. Some anthropologists speculate that Stone Age societies performed trepanning on people with mental illnesses to release evil spirits or demons from their heads. In the absence of written records, however, it is impossible to know why the operation was performed.



Ancient Societies


The Greek physician Hippocrates was one of the first scholars to challenge the notion that disease was punishment sent from the gods. He believed that all illnesses, including mental illnesses, had natural origins.

Culver Pictures

The literature of ancient Greece and Rome contains evidence of the belief that spirits or demons cause mental illness. In the 5th century bc the Greek historian Herodotus wrote an account of a king who was driven mad by evil spirits. The legend of Hercules describes how, driven insane by a curse, he killed his own children. The Roman poets Virgil and Ovid repeated these themes in their works. The early Babylonian, Chinese, and Egyptian civilizations also viewed mental illness as possession, and used exorcism—which sometimes involved beatings, restraint, and starvation—to drive the evil spirits from their victim.

Not all ancient scholars agreed with this theory of mental illness. The Greek physician Hippocrates believed that all illnesses, including mental illnesses, had natural origins. For example, he rejected the prevailing notion that epilepsy had its origins in the divine or sacred, viewing it as a disease of the brain. Hippocrates classified mental illnesses into categories that included mania, melancholia (depression), and phrenitis (brain fever), and he advocated humane treatment that included rest, bathing, exercise, and dieting. The Greek philosopher Plato, although adhering to a somewhat supernatural view of mental illness, believed that childhood experiences shaped adult behaviors, anticipating modern psychodynamic theories by more than 2000 years.



The Middle Ages

The Middle Ages in Europe, from the fall of the Roman empire in the 5th century ad to about the 15th century, was a period in which religious beliefs, specifically Christianity, dominated concepts of mental illness. Much of society believed that mentally ill people were possessed by the devil or demons, or accused them of being witches and infecting others with madness (see Witchcraft). Thus, instead of receiving care from physicians, the mentally ill became objects of religious inquisition and barbaric treatment. On the other hand, some historians of medicine cite evidence that even in the Middle Ages, many people believed mental illness to have its basis in physical and psychological disturbances, such as imbalances in the four bodily humors (blood, black bile, yellow bile, and phlegm), poor diet, and grief.

The Islamic world of North Africa, Spain, and the Middle East generally held far more humane attitudes toward people with mental illnesses. Following the belief that God loved insane people, communities began establishing asylums beginning in the 8th century ad, first in Baghdād and later in Cairo, Damascus, and Fez. The asylums offered patients special diets, baths, drugs, music, and pleasant surroundings.



The Renaissance

The Renaissance, which began in Italy in the 14th century and spread throughout Europe in the 16th and 17th centuries, brought both deterioration and progress in perceptions of mental illness. On the one hand, witch-hunts and executions escalated throughout Europe, and the mentally ill were among those persecuted. The infamous Malleus Maleficarum,which served as a handbook for inquisitors, claimed that witches could be identified by delusions, hallucinations, or other peculiar behavior. To make matters worse, many of the most eminent physicians of the time fervently advocated these beliefs.

On the other hand, some scholars vigorously protested these supernatural views and called renewed attention to more rational explanations of behavior. In the early 16th century, for example, the Swiss physician Paracelsus returned to the views of Hippocrates, asserting that mental illnesses were due to natural causes. Later in the century, German physician Johann Weyer argued that witches were actually mentally disturbed people in need of humane medical treatment.



The Age of Enlightenment

Pinel Frees the Insane

French physician Philippe Pinel supervises the unchaining of mentally ill patients in 1794 at La Salpêtrière, a large hospital in Paris. Pinel believed in treating mentally ill people with compassion and patience, rather than with cruelty and violence. This painting, Pinel Frees the Insane from Their Chains, was completed by French artist Tony Robert-Fleury in 1876.

Belzeaux/Photo Researchers, Inc.

During the Age of Enlightenment, in the 18th and early 19th centuries, people with mental illnesses continued to suffer from poor treatment. For the most part, they were left to wander the countryside or committed to institutions. In either case, conditions were generally wretched. One mental hospital, the Hospital of Saint Mary of Bethlehem in London, England, became notorious for its noisy, chaotic conditions and cruel treatment of patients (see Bedlam).


The Hospital of Saint Mary of Bethlehem, a London mental hospital commonly known as Bedlam, sold admission tickets to the public in the 18th century, becoming a popular tourist attraction. In this engraving by English artist William Hogarth, part of his series A Rake’s Progress (1735), two women (seen in the background) tour the hospital, watching the mentally ill patients for their amusement. The hospital became notorious for its miserable conditions and cruel treatment of patients.

Art Resource, NY

Yet as the public’s awareness of such conditions grew, improvements in care and treatment began to appear. In 1789 Vincenzo Chiarugi, superintendent of a mental hospital in Florence, Italy, introduced hospital regulations that provided patients with high standards of hygiene, recreation and work opportunities, and minimal restraint. At nearly the same time, Jean-Baptiste Pussin, superintendent of a ward for “incurable” mental patients at La Bicêtre hospital in Paris, France, forbade staff to beat patients and released patients from shackles. Philippe Pinel continued these reforms upon becoming chief physician of La Bicêtre’s ward for the mentally ill in 1793. Pinel began to keep case histories of patients and developed the concept of “moral treatment,” which involved treating patients with kindness and sensitivity, and without cruelty or violence. In 1796 a Quaker named William Tuke established the York Retreat in rural England, which became a model of compassionate care. The retreat enabled people with mental illnesses to rest peacefully, talk about their problems, and work. Eventually these humane techniques became widespread in Europe.



Reform in the United States

Clifford Beers

In 1908, after his release from a mental asylum, Clifford Whittingham Beers wrote A Mind That Found Itself, which exposed the poor conditions he had suffered while confined. He went on to establish several organizations dedicated to the promotion of mental health reforms in the United States.

Library of Congress

People living in the colonies of North America in the 17th and 18th centuries generally explained bizarre or deviant behavior as God’s will or the work of the devil. Some people with mental illnesses received care from their families, but most were jailed or confined in almshouses with the poor and infirm. By the mid-18th century, however, American physicians came to view mental illnesses as diseases of the brain, and advocated specialized facilities to treat the mentally ill. The Pennsylvania Hospital in Philadelphia, which opened in 1752, became the first hospital in the American colonies to admit people with mental illnesses, housing them in a separate ward. However, in the hospital’s early years, mentally ill patients were chained to the walls of dark, cold cells.

In the 1780s American physician Benjamin Rush instituted changes at the Pennsylvania Hospital that greatly improved conditions for mentally ill patients. Although he endorsed the continued use of restraints, punishment, and bleeding, he also arranged for heat and better ventilation in the wards, separation of violent patients from other patients, and programs that offered work, exercise, and recreation to patients. Between 1817 and 1828, following the examples of Tuke and Pinel, a number of institutions opened that devoted themselves exclusively to the care of mentally ill people. The first private mental hospital in the United States was the Asylum for the Relief of Persons Deprived of the Use of Their Reason (now Friends Hospital), opened by Quakers in 1817 in what is now Philadelphia. Other privately established institutions soon followed, and state-sponsored hospitals—in Kentucky, New York, Virginia, and South Carolina—-opened beginning in 1824.

Dorothea Dix

American reformer Dorothea Dix championed the causes of prison inmates, the mentally ill, and the destitute. Horrified by the conditions provided for the mentally ill in Massachusetts, Dix successfully petitioned the state government for improvements in 1843. She was directly responsible for building or enlarging 32 mental hospitals in North America, Europe, and Japan.


Nevertheless, circumstances for most mentally ill people in the United States, especially those who were poor, remained dreadful. In 1841 Dorothea Dix, a Boston schoolteacher, began a campaign to make the public aware of the plight of mentally ill people. By 1880, as a direct result of her efforts, 32 psychiatric hospitals for the poor had opened. Increasingly, society viewed psychiatric institutions as the most appropriate form of care for people with mental illnesses. However, by the late 19th century, conditions in these institutions had deteriorated. Overcrowded and understaffed, psychiatric hospitals had shifted their treatment approach from moral therapy to warehousing and punishment. In 1908 Clifford Whittingham Beers aroused new concern for mentally ill individuals with the publication of A Mind That Found Itself, an account of his experiences as a mental patient. In 1909 Beers founded the National Committee for Mental Hygiene, which worked to prevent mental illness and ensure humane treatment of the mentally ill.



Deinstitutionalization Movement

Following World War II (1939-1945), a movement emerged in the United States to reform the system of psychiatric hospitals, in which hundreds of thousands of mentally ill persons lived in isolation for years or decades. Many mental health professionals—seeing that large state institutions caused as much, if not more, harm to patients than mental illnesses themselves—came to believe that only patients with severe symptoms should be hospitalized. In addition, the development in the 1950s of antipsychotic drugs, which helped to control bizarre and violent behavior, allowed more patients to be treated in the community. In combination, these factors led to the deinstitutionalization movement: the release, over the next four decades, of hundreds of thousands of patients from state mental hospitals. In 1950, 513,000 patients resided in these institutions. By 1965 there were 475,000, and by 1990 state mental hospitals housed only 92,000 patients on any given night. Many patients who were released returned to their families, although many were transferred to questionable conditions in nursing homes or board-and-care homes. Many patients had no place to go and began to live on the streets.

The National Mental Health Act of 1946 created the National Institute of Mental Health as a center for research and funding of research on mental illness. In 1955 Congress created a commission to investigate the state of mental health care, treatment, and prevention. In 1963, as a result of the commission’s findings, Congress passed the Community Mental Health Centers Act, which authorized the construction of community mental health centers throughout the country. Implementation of these centers was not as extensive as originally planned, and many people with severe mental illnesses failed to receive care of any kind.



Recent Developments

One of the most important developments in the field of mental health in the United States has been the establishment of advocacy and support groups. The National Alliance for the Mentally Ill (NAMI), one of the most influential of these groups, was founded in 1972. NAMI’s goal is to improve the lives of people with severe mental illnesses and their families by eliminating discrimination in housing and employment and by improving access to essential treatments and programs.

During the 1980s, all levels of government in the United States cut back on funding for social services. For example, the Social Security Administration discontinued benefits for approximately 300,000 people between 1981 and 1983. Of these, an estimated 100,000 were people with mental illnesses. Although the government eventually restored Social Security benefits to many of these people, the interruption of services caused widespread hardship.

The emergence of managed care in the 1990s as a way to contain health care costs had a tremendous impact on mental health care in the United States. Health insurance companies and health maintenance organizations increasingly scrutinized the effectiveness of various psychotherapies and drug treatments and put stricter limits on mental health care. In response to these restrictions, Congress passed the Mental Health Parity Act of 1996. This law required private medical plans that offer mental health coverage to set equal yearly and lifetime payment limits for coverage of both mental and physical illnesses.

In 1997 the U.S. Equal Employment Opportunity Commission issued new guidelines intended to prevent discrimination against people with mental illnesses in the workplace. The rules, based on the Americans with Disabilities Act of 1990, prohibit employers from asking job applicants if they have a history of mental illness and require employers to provide reasonable accommodations to workers with mental illnesses.

In recent years international agencies, led by the World Health Organization (WHO) of the United Nations (UN) have developed mental health policies that seek to reduce the huge burden of mental illness worldwide. These agencies are working to improve the quality of mental health services in Africa, Asia, Latin America, the Middle East, and elsewhere by educating governments on prevention and treatment of mental illness and on the rights of the mentally ill.

Contributed By:
Alex Cohen
Arthur M. Kleinman

Microsoft ® Encarta ® 2009. © 1993-2008 Microsoft Corporation. All rights reserved.