Science

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Modern Science

In the 20th century, scientists achieved spectacular advances in the fields of genetics, medicine, social sciences, technology, and physics.

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Genetics

At the beginning of the 20th century, the life sciences entered a period of rapid progress. Mendel's work in genetics was rediscovered in 1900, and by 1910 biologists had become convinced that genes are located in chromosomes, the threadlike structures that contain proteins and deoxyribonucleic acid (DNA). During the 1940s American biochemists discovered that DNA taken from one kind of bacterium could influence the characteristics of another. From these experiments, it became clear that DNA is the chemical that makes up genes and thus the key to heredity.

After American biochemist James Watson and British biophysicist Francis Crick established the structure of DNA in 1953, geneticists became able to understand heredity in chemical terms. Since then, progress in this field has been astounding. Scientists have identified the complete genome, or genetic catalog, of the human body (see Human Genome Project). In many cases, scientists now know how individual genes become activated and what effects they have in the human body. Genes can now be transferred from one species to another, side-stepping the normal processes of heredity and creating hybrid organisms that are unknown in the natural world (see Transgenic Organism).

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Medicine

At the turn of the 20th century, Dutch physician Christiaan Eijkman showed that disease can be caused not only by microorganisms but by a dietary deficiency of certain substances now called vitamins. In 1909 German bacteriologist Paul Ehrlich introduced the world's first bactericide, a chemical designed to kill specific kinds of bacteria without killing the patient's cells as well. Following the discovery of penicillin in 1928 by British bacteriologist Sir Alexander Fleming, antibiotics joined medicine’s chemical armory, making the fight against bacterial infection almost a routine matter. Antibiotics cannot act against viruses, but vaccines have been used to great effect to prevent some of the deadliest viral diseases. Smallpox, once a worldwide killer, was completely eradicated by the late 1970s, and in the United States the number of polio cases dropped from 38,000 in the 1950s to less than 10 a year by the 21st century.

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By the middle of the 20th century scientists believed they were well on the way to treating, preventing, or eradicating many of the most deadly infectious diseases that had plagued humankind for centuries. But by the 1980s the medical community’s confidence in its ability to control infectious diseases had been shaken by the emergence of new types of disease-causing microorganisms. New cases of tuberculosis developed, caused by bacteria strains that were resistant to antibiotics. New, deadly infections for which there was no known cure also appeared, including the viruses that cause hemorrhagic fever and the human immunodeficiency virus (HIV), the cause of acquired immunodeficiency syndrome.

In other fields of medicine, the diagnosis of disease has been revolutionized by the use of new imaging techniques, including magnetic resonance imaging and computed tomography. Scientists were also on the verge of success in curing some diseases using gene therapy, in which the insertion of normal or genetically altered genes into a patient’s cells replaces nonfunctional or missing genes.

Improved drugs and new tools have made surgical operations that were once considered impossible now routine. For instance, drugs that suppress the immune system enable the transplant of organs or tissues with a reduced risk of rejection (see Medical Transplantation). Endoscopy permits the diagnosis and surgical treatment of a wide variety of ailments using minimally invasive surgery. Advances in high-speed fiber-optic connections permit surgery on a patient using robotic instruments controlled by surgeons at another location. Known as telemedicine, this form of medicine makes it possible for skilled physicians to treat patients in remote locations or places that lack medical help.

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Social Sciences

In the 20th century the social sciences emerged from relative obscurity to become prominent fields of research. Austrian physician Sigmund Freud founded the practice of psychoanalysis, creating a revolution in psychology that led him to be called the 'Copernicus of the mind.” In 1948 the American biologist Alfred Kinsey published Sexual Behavior in the Human Male, which proved to be one of the best-selling scientific works of all time. Although criticized for his methodology and conclusions, Kinsey succeeded in making human sexuality an acceptable subject for scientific research.

The 20th century also brought dramatic discoveries in the field of anthropology, with new fossil finds helping to piece together the story of human evolution. A completely new and surprising source of anthropological information became available from studies of the DNA in mitochondria, cell structures that provide energy to fuel the cell’s activities. Mitochondrial DNA has been used to track certain genetic diseases and to trace the ancestry of a variety of organisms, including humans.

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Technology

In the field of communications, Italian electrical engineer Guglielmo Marconi sent his first radio signal across the Atlantic Ocean in 1901. American inventor Lee De Forest invented the triode, or vacuum tube, in 1906. The triode eventually became a key component in nearly all early radio, radar, television, and computer systems. In 1920 Scottish engineer John Logie Baird developed the Baird Televisor, a primitive television that provided the first transmission of a recognizable moving image. In the 1920s and 1930s American electronic engineer Vladimir Kosma Zworykin significantly improved the television’s picture and reception. In 1935 British physicist Sir Robert Watson-Watt used reflected radio waves to locate aircraft in flight. Radar signals have since been reflected from the Moon, planets, and stars to learn their distance from Earth and to track their movements (see Radar Astronomy).

In 1947 American physicists John Bardeen, Walter Brattain, and William Shockley invented the transistor, an electronic device used to control or amplify an electrical current. Transistors are much smaller, far less expensive, require less power to operate, and are considerably more reliable than triodes. Since their first commercial use in hearing aids in 1952, transistors have replaced triodes in virtually all applications.

During the 1950s and early 1960s minicomputers were developed using transistors rather than triodes. Earlier computers, such as the electronic numerical integrator and computer (ENIAC), first introduced in 1946 by American physicist John W. Mauchly and American electrical engineer John Presper Eckert, Jr., used as many as 18,000 triodes and filled a large room. But the transistor initiated a trend toward microminiaturization, in which individual electronic circuits can be reduced to microscopic size. This drastically reduced the computer's size, cost, and power requirements and eventually enabled the development of electronic circuits with processing speeds measured in billionths of a second .

Further miniaturization led in 1971 to the first microprocessor—a computer on a chip. When combined with other specialized chips, the microprocessor becomes the central arithmetic and logic unit of a computer smaller in size than a portable typewriter. With their small size and a price less than that of a used car, today’s personal computers are many times more powerful than the physically huge, multimillion-dollar computers of the 1950s. Once used only by large businesses, computers are now used by professionals, small retailers, and students to perform a wide variety of everyday tasks, such as keeping data on clients, tracking budgets, and writing school reports. People also use computers to interface with worldwide communications networks, such as the Internet and the World Wide Web, to send and receive e-mail, to shop, or to find information on just about any subject.

During the early 1950s public interest in space exploration developed. The focal event that opened the space age was the International Geophysical Year from July 1957 to December 1958, during which hundreds of scientists around the world coordinated their efforts to measure the Earth’s near-space environment. As part of this study, both the United States and the Soviet Union announced that they would launch artificial satellites into orbit for nonmilitary space activities.

When the Soviet Union launched the first Sputnik satellite in 1957, the feat spurred the United States to intensify its own space exploration efforts. In 1958 the National Aeronautics and Space Administration (NASA) was founded for the purpose of developing human spaceflight. Throughout the 1960s NASA experienced its greatest growth. Among its achievements, NASA designed, manufactured, tested, and eventually used the Saturn rocket and the Apollo spacecraft for the first manned landing on the Moon in 1969 (see Apollo Program). In the 1960s and 1970s, NASA also developed the first robotic space probes to explore the planets Mercury, Venus, and Mars (see Mariner). The success of the Mariner probes paved the way for the unmanned exploration of the outer planets in Earth’s solar system.

In the 1970s through 1990s, NASA focused its space exploration efforts on a reusable space shuttle, which was first deployed in 1981. In 1998 the space shuttle, along with its Russian counterpart known as Soyuz, became the workhorses that enabled the construction of the International Space Station.