The systematic approach to biology started with the Greek philosophers about 2,500 years ago. Aristotle (384-322 B.C.) is considered the "father of biology" for his classification of animals and for performing the first known biology experiments, dissecting plants and animals and studying the development of the chick in its egg. His student Theophrastus (ca. 372-286 B.C.) laid the foundation of botany, describing and classifying more than 500 plants and also describing the ways plants can germinate and grow. In Roman times, Lucretius (99-55 B.C.) proposed one of the earliest theories of evolution. But other than medical knowledge, biology made little progress until after the Middle Ages.
In the 15th and 16th centuries Europeans explored the Americas and some of the Pacific islands, and regular contact between Europe and southern Africa and eastern Asia was instituted. As a result European scholars were exposed to a great variety of plants and animals that were new to them. They responded with books describing and classifying both newfound and familiar plants and animals, starting as early as 1530. A few years later the first botanical gardens began to be established. When the scientific revolution of the 17th century began, scientists undertook more detailed experiments in biology. For example, Jan van Helmont (1579-1694) carefully measured the weight of soil in a tub as a willow grew there, establishing that the increase in mass of the willow was much greater than any diminution of mass of the soil.
Also in the 17th century, biologists began to use an important new tool, the microscope (probably invented in 1595). A previously unseen world opened, beginning with the identification and naming of capillaries (1660), cells (1665), the various tiny organs of insects (1669) and plants (1675), sperm (1667), protists (1673), and bacteria (1683). Microscopic studies contributed to increasingly sophisticated methods of classification of organisms; in 1735 these methods took the basic shape that taxonomy has retained until today, although with many refinements and improvements.
In the 19th century, biology advanced with two overarching theories that have been central to the science ever since. A number of scientists from as early as 1668 had performed experiments to show that life arises only from life and is not spontaneously generated from non-living matter. In 1838 and 1839, Matthias Schleiden (1804-81) and Theodor Schwann (1810-82) concluded that living things are composed of cells and that reproduction always begins with cells. Since then the cell theory has been confirmed over and over, whether for single-celled bacteria or protists or for the largest organisms, giant trees and whales. About the same time, Charles Darwin (1809-82) began to formulate his theory of evolution by natural selection, published as The Origin of Species in 1859. Darwin's theory provides a framework in time and space that can be used to analyze almost all biological topics ranging from animal behavior to changes in the chemicals that cells employ in respiration.
A third unifying idea also began in the mid-19th century, but few knew of it at the time. Gregor Mendel (1822-84) had by 1865 discovered from experiment the basic laws of heredity, but his work was described to a local scientific society and published in its journal. In 1900, Mendel's work was rediscovered and the science of genetics began. Chromosomes were recognized as the carriers of genes (the units of heredity) as early as 1902. In 1907, Thomas Hunt Morgan (1866-1945) began a long series of experiments with fruit flies that detailed the relationship between heredity and development of traits in organisms.
Biologists also pursued the details of basic life processes (respiration, nutrition, synthesis, excretion, transport, regulation, growth, reproduction). As early as 1779, Jan Ingenhousz (1730-99) recognized the essentials of photosynthesis, which is the basis of both respiration and nutrition for nearly all forms of life; however, the chemical pathways involved were not firmly identified until 1957. The role of vitamins in nutrition began to be understood in 1901, chemical control of life processes through hormones began to be unraveled in 1902, and the chemical transmission of nerve impulses was first identified in 1920. Similarly, the chemical bases of metabolism and respiration were uncovered during the first half of the 20th century, and the details of growth and development became one of the main advances of the second half of that century.
Other 20th-century advances involved the recognition of both the study of complex interactions of organisms in particular environments, which became the science of ecology and also of animal behavior, or the science of ethology.
Biology obtained a new basis in the advances of genetics, which began with the study of heredity at the beginning of the 20th century and reached a high point when the human genome (totality of genes) was almost completely deciphered, as announced in 2003. Along the way, advances in genetics had included the recognition that genes are found in the DNA of chromosomes (1944), the discovery of the structure of DNA (1953), working out the genetic code (1961-68), the invention of genetic engineering by inserting genes from one species into another (1972-73), deciphering the genomes of viruses (1977), using DNA to unravel evolutionary relationships (1981), sequencing the genome of a bacterium (1995), and cloning the first mammal with a set of genes taken from an adult body cell (1997).
(‘The New York Times Guide to Essential Knowledge’)