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The Theory of Natural Selection

In the 1800s, Charles Darwin, a British naturalist, developed the theory of natural selection in his book “On the Origin of Species by Means of Natural Selection”. Darwin had the opportunity to travel around the world as the naturalist on a British survey ship. Wherever Dar­win visited, he saw a large number of different kinds of plants and animals and noted how well they were adapted to their particular situations.

He determined that there were several factors that could interact together to allow for natural selection:

1. Individuals within a species showed variation; some of the variations were very useful and others were not. For example, individual animals that are part of the same species show different colour variations. Some colours make the animal more conspicuous while others are less conspicuous.

2. Organisms within a species typically produce many more offspring than can survive. This means that here is not enough suitable habitat for all of the offspring to grow to maturity. A pair of rabbits may have three to four litters of offspring each sum­mer with several young in each litter.

3. Because of the excess number of individuals, there is a struggle for survival. Individuals within the population must compete with each other for food, space, mates, or other requirements that are in limited supply.

Great horned owls and other large owls typically produce two young at a time, but if food is in short supply, the larger of the two young will get the majority of the food.

4. Because of variation among individuals, some would have a greater chance of surviving and reproducing than others. The competition for resources often results in the less fit individuals dying; therefore, they do not get a chance to reproduce themselves. Even if they do not die, they may mature more slowly and not be able to repro­duce as many times as the more fit members of the species.

5. As time passes and each generation is subjected to the same kind of process, there will be an increase in the percentage of individuals showing the favorable variations and a decrease in those having unfavorable variations. The species will become better adapted to its environment.

Задание 1. Закончите предложения:

1. Charles Darwin developed the theory of ….

2. Individuals within a species showed ….

3. Organisms within a species typically produce ….

4. Individuals within the population must compete with each other for ….

5. The competition for resources often results in ….

Задание 2. Прочитайте примеры естественного отбора из текста.

Modern Veterinary Care

The zoo veterinarian attends to the needs of every animal in the zoo habitat, from the tiniest shrew to the largest elephant, monitoring diet, dental health, and even reproduction. Zoo veterinarians perform blood tests, vaccinations, routine examinations, and even surgery. They manage endangered species to encourage successful mating and reproduction. For pandas, which are solitary in the wild, this might involve isolating individuals during the non-breeding season, and then bringing a pair together to mate when the time is right.

Veterinarians employed in regulatory medicine are responsible for controlling or eliminating certain diseases and protecting the public from animal diseases that can affect people. As food inspectors, they identify diseased livestock and unsafe meat and poultry. Regulatory medicine veterinarians also prevent foreign diseases from entering the country by enforcing quarantines and inspecting animals. They supervise interstate shipments of animals, test for the presence of diseases, and manage campaigns to prevent and eradicate diseases that threaten animal and human health such as tuberculosis, undulant fever, and rabies. Some public health veterinarians evaluate the safety of food processing plants, restaurants, and water supplies. Those in environmental health programs study and evaluate how various pesticides, industrial pollutants, and other contaminants affect human and animal populations. Other public health veterinarians are epidemiologists (specialists who study the cause and incidence of diseases). Public health veterinarians employed in government and private laboratories provide important diagnostic and testing services. They might, for example, inspect beef to insure that it does not contain E. coli bacteria or chicken to insure that it is free of Salmonella bacteria.

Задание 1. Соедините две части предложения:

1. The zoo veterinarian … 2. Food inspectors … 3. Regulatory medicine veterinarians … 4. Epidemiologists … 5. Some public health veterinarians…

identify unsafe meat and poultry. study the cause and incidence of diseases. perform blood tests, vaccinations, routine examinations. evaluate the safety of food processing plants. manage campaigns to prevent and eradicate diseases that threaten animal and human health.

Задание 2. Ответьте на вопрос:

What are the duties of public health veterinarians?

History of Microbiology

Microbiology began with the development of the microscope in the

17th and 18th centuries. By 1680 the Dutch scientist Anthony van Leeuwenhoek had produced a simple hand-held device that allowed scientists to view a variety of microbes – which Leeuwenhoek called “animalcules” – in stagnant water and in scrapings from teeth.

In the late 1700s Edward Jenner conducted the first vaccinations, using cowpox virus to protect people against smallpox. Later an altered form of the rabies virus was used to protect against the dreadful disease rabies. Vaccines remain the major means of protection against most viral infections.

Modern microbiology had its origins in the work of the French scientist Louis Pasteur – considered the father of microbiology – who developed methods of culturing and identifying microbes. During the second half of the 19th century, he and his contemporary Robert Koch provided final proof of the germ theory of disease. Pasteur was the first to propose that microbes cause chemical changes as they grow. Koch derived a central principle of modern microbiology, known as Koch’s Postulate that determines whether a particular germ causes a given disease.

Pasteur and his contemporaries developed pure culture methods for the growth of microbes. Another great advance in pure culture methods came in the late 19th century, when microbiologists discovered that each kind of microbe preferred a certain medium for optimal growth. In 1929 Alexander Fleming observed that molds can produce a substance that prevents the growth of bacteria. His discovery, an antibiotic is called penicillin, was later isolated and produced commercially to protect people against the harmful effects of certain microorganisms. Today several kinds of penicillin are synthesized from various species of the mold Penicillium and used for different therapeutic purposes. In the 1940s microbiology expanded into the fields of molecular biology and genetics. Viruses were found to be simple microbes that could be studied quantitatively, and they themselves were used to study the nature of deoxyribonucleic acid, or DNA Scientists found that DNA could be removed from living cells and spliced together in any combination. They were able to alter the genetic code dictating the entire structure and function of cells, tissues, and organs.

Задание 1. Соотнесите имя ученого с его вкладом в науку:

Anthony van Leeuwenhoek Edward Jenner Louis Pasteur Robert Koch Alexander Fleming

provided final proof of the germ theory of disease. produced a simple hand-held device that allowed scientists to view a variety of microbes. conducted the first vaccinations. observed that molds can produce a substance that prevents the growth of bacteria. 5. developed methods of culturing and identifying microbes.

Задание 2. Перескажите текст на родном языке.