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1.1The Birth of Life Science

From 5 to 4 B.C., Hippocrates of Greece studied medicine and established it as a science by discarding superstition. He is famous today for his theory of the four humors, which stated that diseases are caused by abnormalities in body fluids. Later, Aristotle founded life science. Aristotle thought that the difference between living and non-living objects was that the former had souls. He classified things that moved and had sensory perceptions as animals, and things that did not as plants. He also thought that the ability to reason was what distinguished humans from animals.
For a long time after Aristotle, life science was not treated as science. In the 17th century, however, the invention of the microscope by Hans and Zacharias Janssen caused a sudden increase in the number of objects being observed, and life science began to progress rapidly thereafter. For example, an Englishman named William Harvey pioneered the field of physiology when he discovered that blood circulates in the human body. In 1665, Robert Hooke discovered cells using a microscope (see Chapter 2), and attention subsequently shifted to the function of cells. During the 18th century, Carl Linnaeus developed the concept of species and proposed a system of binomial nomenclature for classifying all organisms. Next, Edward Jenner discovered vaccination, a great accomplishment in medicine. In the 19th century, Claude Bernard introduced the concept of constancy of the internal environment, and Walter B. Cannon later developed the concept of homeostasis. Homeostasis, a fundamental property of living organisms, is the tendency for the inside of an organism to remain constant regardless of changes in its internal and external environments. This discovery gave birth to the concept of health. During the same period, life science was revolutionized by Darwin's proposal of evolution and Mendel's discovery of the laws of heredity (see Chapter 3). It can be said that the foundation of modern life science had been laid at this point.

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