PASSAGE 1 – Questions 1-10

A new study, conducted by scientists from Oxford University, the Chinese Academy of Medical Sciences and the Chinese Center for Disease Control, has warned that a third of all men currently under the age of 20 in China will eventually die prematurely if they do not give up smoking.

The research, published in The Lancet medical journal, says two-thirds of men in China now start to smoke before 20. Around half of those men will die from the habit, it concludes.

In 2010, around one million people in China died from tobacco usage. But researchers say that if current trends continue, that will double to two million people - mostly men - dying every year by 2030, making it a "growing epidemic of premature death".

But co-author Richard Peto said there was hope - if people can be persuaded to quit. "The key to avoid this huge wave of deaths is cessation, and if you are a young man, don't start," he said.

In many parts of China, meals often fit a comfortable pattern. After putting down their chopsticks, men commonly push their chairs back from the table and light cigarettes. No wonder China has struggled to impose a smoking ban in public places. Here, relationships are often built amid clouds of smoke.

Expensive brands of cigarettes, often decorated with gold detailing on the cartons, are given as gifts. And ordinary brands are affordable to all but the very poor, costing just 2.5 yuan ($0.4; £0.25) a pack.

In a country where smoking is so ingrained in daily life, few understand the harmful effects of tobacco use. According to the World Health Organization (WHO), only 25% of Chinese adults can list the specific health hazards of smoking, from lung cancer to heart disease.

Perhaps it should come as no surprise, then, that only 10% of Chinese smokers quit by choice. Instead, most are forced to give up their cigarettes because they're too sick to continue.
While smoking rates have fallen in developed countries - to less than one in five in the US - they have risen in China, as cigarettes have become more available and consumers richer.

Authorities have shown concern over the rise, with Beijing even introducing a public smoking ban. But efforts have been hampered by the habit's popularity, and its usefulness as a source of tax - the government collects about 428 billion yuan (£44billion, $67billion) in tobacco taxes each year.

Globally, tobacco kills up to half of its users, according to the World Health Organization.

PASSAGE 2 – Questions 11-20

The evidence that humans are causing global warming is strong, but the question of what to do about it remains controversial. Economics, sociology, and politics are all important factors in planning for the future.

Even if we stopped emitting greenhouse gases (GHGs) today, the Earth would still warm by another degree Fahrenheit or so. But what we do from today forward makes a big difference. Depending on our choices, scientists predict that the Earth could eventually warm by as little as 2.5 degrees or as much as 10 degrees Fahrenheit.

A commonly cited goal is to stabilize GHG concentrations around 450-550 parts per million (ppm), or about twice pre-industrial levels. This is the point at which many believe the most damaging impacts of climate change can be avoided. Current concentrations are about 380 ppm, which means there isn't much time to lose. According to the IPCC, we'd have to reduce GHG emissions by 50% to 80% of what they're on track to be in the next century to reach this level.

Is this possible?

Many people and governments are already working hard to cut greenhouse gases, and everyone can help.

Researchers Stephen Pacala and Robert Socolow at Princeton University have suggested one approach that they call "stabilization wedges." This means reducing GHG emissions from a variety of sources with technologies available in the next few decades, rather than relying on an enormous change in a single area. They suggest 7 wedges that could each reduce emissions, and all of them together could hold emissions at approximately current levels for the next 50 years, putting us on a potential path to stabilize around 500 ppm.

There are many possible wedges, including improvements to energy efficiency and vehicle fuel economy (so less energy has to be produced), and increases in wind and solar power, hydrogen produced from renewable sources, biofuels (produced from crops), natural gas, and nuclear power. There is also the potential to capture the carbon dioxide emitted from fossil fuels and store it underground—a process called "carbon sequestration."

In addition to reducing the gases we emit to the atmosphere, we can also increase the amount of gases we take out of the atmosphere. Plants and trees absorb CO2 as they grow, "sequestering" carbon naturally. Increasing forestlands and making changes to the way we farm could increase the amount of carbon we're storing.

Some of these technologies have drawbacks, and different communities will make different decisions about how to power their lives, but the good news is that there are a variety of options to put us on a path toward a stable climate.

PASSAGE 3 – Questions 1-10

Art communicates to us primarily through our eyes. We look at art, and we try to find some meaning in the experience. If we are to begin to think about art more seriously, we might do well to become more aware of the process of seeing itself.

Science tells us that seeing is a mode of perception, or the recognition and interpretation of sensory data-in other words, how information comes in our senses, and what we make of it. In visual perception our eyes take in information in the form of light patterns; the brain processes these patterns to give them meaning. The mechanics of perception work much the same way for everyone, yet in a given situation we do not all see the same things.

We can take great pleasure in merely looking at art, just as we take pleasure in the view of a distant mountain range or watching the sun set over the ocean. But art, unlike nature, is a human creation. It is one of the many ways we express ourselves and attempt to communicate. A work of art is the product of human intelligence, and we can meet it with our own intelligence on equal footing. This is where study comes in.

The understanding of process - the how - often contributes quite a lot to our appreciation of art. If you understand why painting in watercolor may be different from painting in oil, why clay responds differently to the artist's hands than does wood or glass - you will have a richer appreciation of the artist's expression.

Knowing the place of a work of art in history - what went before and came after - can also deepen your understanding. Artists learn to make art by studying the achievements of the past and observing the efforts of their contemporaries. They adapt ideas to serve their own needs and then bequeath those ideas to future generations of artists. For example, Matisse assumed that his audience would know that Venus was the ancient Roman goddess of love. But he also hoped that they would be familiar with one Venus in particular, a famous Greek statue known as the Venus de Milo.

An artist may create a specific work for any of a thousand reasons. An awareness of the why may give some insight as well. Looking at Van Gogh's The Starry Night, it might help you know that Van Gogh was intrigued by the belief that people journeyed to a star after their death, and that there they continued their lives. "Just as we take the train to get to Tarascon or Rouen," he wrote in a letter, "we take death to reach a star." This knowledge might help you understand why Van Gogh felt so strongly about the night sky, and what his painting might have meant to him.

But no matter how much you study, Van Gogh's painting will never mean for you exactly what it meant for him, nor should it. Great works of art hold many meanings. The greatest of them seem to speak anew to each generation and to each attentive observer. The most important thing is that they mean something for you, that your own experiences, thoughts, and emotions find a place in them.

PASSAGE 4 – Questions 11-20

Antibiotics block the life cycle of bacteria that invade the human body. The first of these antibiotics, penicillin, works by blocking the molecules that construct the cell walls of particular bacteria. The bacteria, with incomplete cell walls, are not able to reproduce.

When penicillin was introduced during World War II, it was truly a "miracle drug." Until that time, anyone who was cut or wounded stood a great risk of infection. Once penicillin became available, the situation changed. Wounded soldiers, children with ear infections, and many others began to benefit from the ability to block the growth of bacteria.

While humanity may have won that particular battle against bacteria, the war is far from over. The reason is that in any bacterial population, there are bound to be a few bacteria that, for one reason or another, are not affected by a particular antibiotic. For example, they may have a slightly differently shaped enzyme that builds cell walls, so that penicillin will not fit onto that particular shape of the enzyme. These bacteria will not be affected by that particular drug.

For that small group, the antibiotic is a real godsend. It doesn't affect them, but it does wipe out all of their competition. They are thus free to multiply, and, over time, all of the bacteria will have whatever properties that made those individuals resistant.

Traditionally, medical scientists have dealt with this phenomenon by developing a large number of antibiotics, each of which intervenes in the bacterial life cycle in a slightly different way.

Consequently, if you happen to have a bacterium that is resistant to one antibiotic, probably it will succumb to the action of another. You may, in fact, have had the experience of going to a doctor with an infection, being given an antibiotic, and then finding that it didn't work. In all likelihood, all your doctor had to do then was prescribe a different antibiotic and everything was fine.

The problem is that as time has passed, more and more bacteria have become resistant to antibiotics. In fact, currently, there is one strain of bacteria- Staphylococcus-that is resistant to every commercially available antibiotic except one, and in 1996, a bacterium with lowered resistance to that last antibiotic appeared in Japan.

The appearance of drug-resistant bacteria is not particularly surprising; in fact, it probably should have been anticipated. Nevertheless, in the late 1980s, there was a general sense of complacency among scientists on the antibiotic question. Little profit was to be made by developing the one-hundred-and-first antibiotic. Drug companies concentrated their efforts on other areas. Therefore, a gap developed between the production of new antibiotics and the development of resistance among bacteria.

By the early 1990s, this gap was recognized and highlighted in several national news magazines. More companies returned to develop new kinds of antibiotics, and currently, a number are undergoing clinical trials. By early in the twenty-first century, some of these new drugs will start to come on the market, and the problem will be "solved," at least for the moment.

Additional research will focus on the processes by which cells repair the constant damage to DNA, but the computer design of new drugs, the development of new antibiotics, and techniques to combat bacteria should remain a top priority.

Time permitted: 60 minutes
Number of questions: 40

Directions: In this section you will read FOUR different passages. Each one is followed by 10 questions about it. For questions 1-40, you are to choose the best answer A, B, C or, to each question. Then, on your answer sheet, find the number of the question and fill in the space that corresponds to the letter of the answer you have chosen. Answer all questions following a passage on the basis of what is stated or implied in that passage. You have 60 minutes to answer all the questions, including the time to transfer your answers to the answer sheet.

PASSAGE 1 – Questions 1-10

Doctors treat patients for free at clinic in Ha Noi

For 20 years, Dang Thi Nhan, 67, has been waking up about 30 minutes earlier each day to bake cakes or prepare tea for two retired doctors in a clinic near her house in Ha Noi's Giap Bat Ward. That is all Nhan can offer as thanks to doctors who provide free health checks for herself, her paralysed husband and their 43-year-old disabled son. "If one day they cannot take care of themselves and need some one to look after, I will do it voluntarily till the day they are gone," Nhan said.

The small clinic, situated on Kim Dong Street, has become familiar to many people in Ha Noi. It was established in 1992 by Dr Truong Thi Hoi To, 84, a former principal of Nam Dinh Medical College, Le Thi Soc, 87, a retired nurse from Saint Paul Municipal Hospital, and Le Thanh Thuoc, the late deputy director of the Viet Nam National Cancer Hospital, who died last year. The clinic used to open every Monday and Thursday. However, after doctor Thuoc died and due to the deteriorating health of the two other medics, the clinic now only opens on Monday mornings at 8 am. Patients not only receive health checks, but they also receive free medicine.

Since 2014, the clinic has treated about 8,500 patients, according to Giap Bat ward's Red Cross Association. On its first days, the clinic faced numerous difficulties due to lack of money. Mrs. To, founder of the clinic, had to spend her own pension and encourage her children and relatives to donate money to purchase medical equipment and medicine. The clinic also had to relocate seven times as To and her co-workers could not afford high rents. Despite these difficulties, they never thought of giving up. "Being able to help my patients brings me unspeakable joy. This is also my life target. It warms my heart to see the happy faces of the patients," To said.

Tran Thi Toan, 64, a patient from Nam Dinh Province, now works as a servant in Ha Noi. She is grateful to doctor To and nurse Soc not just for the free treatment, but for their caring manner. Toan said: "They give me meticulous treatment and clear, detailed instruction as well as advise me on a healthy and happy lifestyle". Toan feels shy about her job, so the doctors' care and compassionate attitude have become her inspiration in life.

To the doctors, the most precious thing they receive from their patients is confidence in their skills, which can only be achieved through ethics and medical excellence. "The success of a doctor does not lies in how much money they earn, but how many people they help", Soc said. Sharing Soc's opinion, To said that "Medical practitioners should not consider their profession as a tool to get rich. They should not benefit from their patients' pain. Patients come first, not money."

PASSAGE 2 – Questions 11-20

To Get a Job in Your 50s, Maintain Friendships in Your 40s.

We hear it all the time: People who are over 50 take longer to find jobs than younger people. Connie Wanberg, a professor at the Carlson School of Management at the University of Minnesota, had long heard gloom-and-doom stories to that effect, but she wondered how strong the data was to support them.

Very, as it turned out. According to a study by Professor Wanberg and others, job seekers over 50 were unemployed 5.8 weeks longer than those from the ages of 30 to 49. That number rose to 10.6 weeks when the comparison group was from 20 to 29. Professor Wanberg and three other researchers - Darla J. Hamann, Ruth Kanfer and Zhen Zhang arrived at those numbers by analyzing and synthesizing hundreds of studies by economists, sociologists and psychologists.

But it is important not to jump to conclusions about the cause, Professor Wanberg said. "It's not very unusual for everybody to think that the reason for the difficulty in finding jobs at 50s is discrimination," she said. That can sometimes be the case, but the reality is that the behavior required to find work does not play to many older people's strengths. Once they become aware of this, they can act to compensate.

In their study, the researchers found that older people on average had smaller social networks than younger people, Professor Wanberg said. This is not necessarily bad – as we age, many of us find that the quality of our relationships is more important than the quantity. But in the job search process, the number of connections we maintain in our professional and personal networks is often critical.

As people age, they also tend to stay in the same job longer, consistent with a pattern of wanting to put down roots. During that time, the skills people have learned and the job search strategies they once used may become outdated - especially as technology evolves ever more quickly.

The cure for these drawbacks is fairly straightforward. Once you hit your early 40s, even if you are not looking for a job, work to learn new skills and stretch yourself, Professor Wanberg said. Also, keep your networks strong by staying in touch with former colleagues and classmates, along with current co-workers and clients whom you don't see regularly, she said.

Finding a job after 50 doesn't have to be as discouraging as it is often portrayed to be, Professor Wanberg said. Just recognize that some of the obstacles you face are inherent to the aging process, she said. She stressed that her findings reflected only averages and that individual behavior varies greatly. Certainly, many older people maintain wide social circles and often learn skills. But in general, older job seekers must take more steps to find employment than younger ones, she said.

Once older workers do find a new employer, they can use their knowledge, wisdom and emotional intelligence qualities that older people often possess in abundance to thrive in their new positions.

B: READING

Time permitted: 60 minutes
Number of questions: 40

Directions: In this section you will read FOUR different passages. Each one is followed by 10 questions about it. For questions 1-40, you are to choose the best answer A, B, C or D, to each question. Then, on your answer sheet, find the number of the question and fill in the space that corresponds to the letter of the answer you have chosen. Answer all questions following a passage on the basis of what is stated or implied in that passage. You have 60 minutes to answer all the questions, including the time to transfer your answers to the answer sheet.

Questions 1-10

Phillis Wheatley was born in Gambia (in Africa) on May 8, 1753 and died in Boston on December 5, 1784.

When she was 7 or 8, she was sold as a slave to John and Susanna Wheatley of Boston. She was named after the ship that brought her to America, The Phillis.

The Poetry Foundation describes her sale:

In August 1761, "in want of a domestic," Susanna Wheatley, ... purchased "a slender, frail female child ... for a trifle"... The captain of the slave ship believed that the waif was terminally ill, and he wanted ... at least a small profit before she died.... The family surmised the girl-who was "of slender frame and evidently suffering from a change of climate," nearly naked, with "no other covering than a quantity of dirty carpet about her" - to be "about seven years old ... from the circumstances of shedding her front teeth." (http://www.poetryfoundation.org/bio/phillis-wheatley)

Phillis was very intelligent. The Wheatley family taught her to read and write, and encouraged her to write poetry. Her first poem "On Messrs. Hussey and Coffin" was published when she was only twelve. In 1770, "An Elegiac Poem, on the Death of that Celebrated Divine, and Eminent Servant of Jesus Christ, the Reverend and Learned George Whitefield" made her famous. It was published in Boston, Newport, and Philadelphia.

When she was eighteen, Phillis and Mrs. Wheatley tried to sell a collection containing twenty-eight of her poems. Colonists did not want to buy poetry written by an African. Mrs. Wheatley wrote to England to ask Selina Hastings, Countess of Huntingdon, for help. The countess was a wealthy supporter of evangelical and abolitionist (anti-slavery) causes. She had Poems on Various Subjects, Religious and Moral published in England in 1773. This book made Phillis famous in England and the thirteen colonies. She wrote a poem for George Washington in 1775, and he praised her work. They met in 1776. Phillis supported independence for the colonies during the Revolutionary War.

After her master died, Phillis was emancipated. She married John Peters, a free black man, in 1778. She and her husband lost two children as infants. John would be imprisoned for debt in 1784. Phillis and her remaining child died in December of 1784 and were buried in an unmarked grave. Nevertheless, the legacy of Phillis Wheatly lives on. She became the first African American and the first slave in the United States to publish a book. She proved that slaves or former slaves had a valuable voice in the Revolutionary era.

Questions 11-20

The conservatism of the early English colonists in North America, their strong attachment to the English way of doing things, would play a major part in the furniture that was made in New England. The very tools that the first New England furniture makers used were, after all, not much different from those used for centuries- even millennia: basic hammers, saws, chisels, planes, augers, compasses, and measures. These were the tools used more or less by all people who worked with wood: carpenters, barrel makers, and shipwrights. At most the furniture makers might have had planes with special edges or more delicate chisels, but there could not have been much specialization in the early years of the colonies.

The furniture makers in those early decades of the 1600' s were known as "joiners," for the primary method of constructing furniture, at least among the English of this time, was that of mortise- and-tenon joinery. The mortise is the hole chiseled and cut into one piece of wood, while the tenon is the tongue or protruding element shaped from another piece of wood so that it fits into the mortise; and another small hole is then drilled (with the auger) through the mortised end and the tenon so that a whittled peg can secure the joint- thus the term "joiner." Panels were fitted into slots on the basic frames. This kind of construction was used for making everything from houses to chests.

Relatively little hardware was used during this period. Some nails- forged by hand- were used, but no screws or glue. Hinges were often made of leather, but metal hinges were also used. The cruder varieties were made by blacksmiths in the colonies, but the finer metal elements were imported. Locks and escutcheon plates - the latter to shield the wood from the metal key- would often be imported. Above all, what the early English colonists imported was their knowledge of, familiarity with, and dedication to the traditional types and designs of furniture they knew in England.

In addition to their military role, the forts of the nineteenth century provided numerous other benefits for the American West. The establishment of these posts opened new roads and provided for the protection of daring adventurers and expeditions as well as established settlers. Forts also served as bases where enterprising entrepreneurs could bring commerce to the West, providing supplies and refreshments to soldiers as well as to pioneers. Posts like Fort Laramie provided supplies for wagon trains traveling the natural highways toward new frontiers. Some posts became stations for the pony express; still others, such as Fort Davis, were stagecoach stops for weary travelers. All of these functions, of course, suggest that the contributions of the forts to the civilization and development of the West extended beyond patrol duty.

Through the establishment of military posts, yet other contributions were made to the development of western culture. Many posts maintained libraries or reading rooms, and some - for example, Fort Davis- had schools. Post chapels provided a setting for religious services and weddings. Throughout the wilderness, post bands provided entertainment and boosted morale. During the last part of the nineteenth century, to reduce expenses, gardening was encouraged at the forts, thus making experimental agriculture another activity of the military. The military stationed at the various forts also played a role in civilian life by assisting in maintaining order, and civilian officials often called on the army for protection.

Certainly, among other significant contributions the army made to the improvement of the conditions of life was the investigation of the relationships among health, climate, and architecture. From the earliest colonial times throughout the nineteenth century, disease ranked as the foremost problem in defense. It slowed construction of forts and inhibited their military functions. Official documents from many regions contained innumerable reports of sickness that virtually incapacitated entire garrisons. In response to the problems, detailed observations of architecture and climate and their relationships to the frequency of the occurrence of various diseases were recorded at various posts across the nation by military surgeons.

Anyone who has handled a fossilized bone knows that it is usually not exactly like its modern counterpart, the most obvious difference being that it is often much heavier. Fossils often have the quality of stone rather than of organic materials, and this has led to the use of the term " petrifaction" (to bring about rock). The implication is that bone, and other tissues, have somehow been turned into stone, and this is certainly the explanation given in some texts. But it is wrong interpretation; fossils are frequently so dense because the pores and other spaces in the bone have become filled with minerals taken up from the surrounding sediments. Some fossil bones have all the interstitial spaces filled with foreign minerals, including the marrow cavity, if there is one, while others have taken up but little from their surroundings. Probably all of the minerals deposited within the bone have been recrystallized from solution by the action of water percolating thru them. The degree of mineralization appears to be determined by the nature of the environment in which the bone was deposited and not by the antiquity of the bone. For example, the black fossil bones that are so common in many parts of Florida are heavily mineralized, but they are only about 20,000 years old, whereas many of the dinosaur bones from western Canada, which are about 75 million years old, are only partially filled in. Under optimum conditions the process of mineralization probably takes thousands rather than millions of years, perhaps considerably less.

The amount of change that has occurred in fossil bone, even in bone as old as that of dinosaurs, is often remarkably small. We are therefore usually able to see the microscopic structures of the bone, including such fine details as the lacunae where the living bone cells once resided. The natural bone mineral, the hydroxyapatite, is virtually unaltered too - it has the same crystal structure as that of modern bone. Although nothing remains of the original collagen, some of its component amino acids are usually still detectable, together with amino acids of the noncollagen proteins of bone.

B: READING

Time permitted: 60 minutes
Number of questions: 40

Directions: In this section you will read FOUR different passages. Each one is followed by 10 questions about it. For questions 1-40, you are to choose the best answer A, B, C or, to each question. Then, on your answer sheet, find the number of the question and fill in the space that corresponds to the letter of the answer you have chosen. Answer all questions following a passage on the basis of what is stated or implied in that passage. You have 60 minutes to answer all the questions, including the time to transfer your answers to the answer sheet.

Questions 1-10

In the last third of the nineteenth century a new housing form was quietly being developed. In 1869 the Stuyvesant, considered New York's first apartment house was built on East Eighteenth Street. The building was financed by the developer Rutherfurd Stuyvesant and designed by Richard Morris Hunt, the first American architect to graduate from the Ecole des Beaux Arts in Paris. Each man had lived in Paris, and each understood the economics and social potential of this Parisian housing form. But the Stuyvesant was at best a limited success. In spite of Hunt's inviting fagade, the living space was awkwardly arranged. Those who could afford them were quite content to remain in the more sumptuous, single-family homes, leaving the Stuyvesant to young married couples and bachelors.

The fundamental problem with the Stuyvesant and the other early apartment buildings that quickly followed, in the 1870's and early 1880's was that they were confined to the typical New York building lot. That lot was a rectangular area 25 feet wide by 100 feet deep - a shape perfectly suited for a row house. The lot could also accommodate a rectangular tenement, though it could not yield the square, well-lighted, and logically arranged rooms that great apartment buildings require. But even with the awkward interior configurations of the early apartment buildings, the idea caught on. It met the needs of a large and growing population that wanted something better than tenements but could not afford or did not want row houses.

So while the city's newly emerging social leadership commissioned their mansions, apartment houses and hotels began to sprout in multiple lots, thus breaking the initial space constraints. In the closing decades of the nineteenth century, large apartment houses began dotting the developed portions of New York City, and by the opening decades of the twentieth century, spacious buildings, such as the Dakota and the Ansonia finally transcended the tight confinement of row house building lots. From there it was only a small step to building luxury apartment houses on the newly created Park Avenue, right next to the fashionable Fifth Avenue shopping area.

Questions 11-20

A snowfall consists of myriads of minute ice crystals that fall to the ground in the form of frozen precipitation. The formation of snow begins with these ice crystals in the subfreezing strata of the middle and upper atmosphere when there is an adequate supply of moisture present. At the core of every ice crystal is a minuscule nucleus, a solid particle of matter around which moisture condenses and freezes. Liquid water droplets floating in the supercooled atmosphere and free ice crystals cannot coexist within the same cloud, since the vapor pressure of ice is less than that of water. This enables the ice crystals to rob the liquid droplets of their moisture and grow continuously. The process can be very rapid, quickly creating sizable ice crystals, some of which adhere to each other to create a cluster of ice crystals or a snowflake. Simple flakes possess a variety of beautiful forms, usually hexagonal, though the symmetrical shapes reproduced in most microscope photography of snowflakes are not usually found in actual snowfalls. Typically, snowflakes in actual snowfall consists of broken fragments and clusters of adhering ice crystals.

For a snowfall to continue once it starts, there must be a constant inflow of moisture to supply the nuclei. This moisture is supplied by the passage of an airstream over a water surface and its subsequent lifting to higher regions of the atmosphere. The Pacific Ocean is the source of moisture for most snowfalls west of the Rocky Mountains, while the Gulf of Mexico and the Atlantic Ocean feed water vapor into the air currents over the central and eastern sections of the United States. Other geographical features also can be the source of moisture for some snowstorms. For example, areas adjacent to the Great Lakes experience their own unique lake-effect storms, employing a variation of the process on a local scale. In addition, mountainous section or rising terrain can initiate snowfalls by the geographical lifting of a moist airstream.

Questions 1-10

Social parasitism involves one species relying on another to raise its young. Among vertebrates, the best known social parasites are such birds as cuckoos and cowbirds; the female lays an egg in a nest belonging to another species and leaves it for the host to rear.

The dulotic species of ants, however, are the supreme social parasites. Consider, for example, the unusual behavior of ants belonging to the genus Polyergus. All species of this ant have lost the ability to care for themselves. The workers do not forage for food. feed their brood or queen, or even dean their own nest. To compensate for these deficits, Polyergus has become specialized at obtaining workers from the related genus Formica to do these chores.

In a raid, several thousand Polyergus workers will travel up to 500 feet in search of a Formica nest, penetrate it, drive off the queen and tier workers, capture the pupal brood, and transport it back to their nest. The captured brood is then reared by the resident Formica workers until the developing pupae emerge to add to the Formica population, which maintains the mixed-species nest Th e Formica workers forage for food and give it to colony members of both species. They also remove wastes and excavate new chambers as the population increases.

The true extent of the Polyergus ants' dependence on the Formica becomes apparent when the worker population grows too large for the existing nest. Formica scouts locate a new nesting site, return to the mixed-species colony, and recruit additional Formica nest mates. During a period that may last seven days, the Formica workers carry to the new nest all the Polyergus eggs, larvae, and pupae, every Polyergus adult, and even the Polyergus queen.

Of the approximately 8,000 species of ants in the world, all 5 species of Polyergus and some 200 species in other genera have evolved some degree of parasitic relationship with other ants.