Biology is the study of living things, i.e., the science of plants, animals (including humans), and microorganisms (see microbiology. Traditionally there were two main branches of biology, the study of animals zoology and the study of plants (botany). Within each of these main branches are a number of divisions dealing with structure (anatomy, cytology), development and function (physiology, embryology), inheritance (genetics, evolution), classification (taxonomy), and interrelations of organisms with each other and their environment (ecology). These branches are also split up into a number of specialist fields, such as mycology, entomology, herpetology.


However, the traditional division into zoology and botany no longer applies since groups of biosciences have developed which span their limits, e.g., microbiology, bacteriology, virology, oceanography, marine biology, and limnology. These are also biosciences that bridge the gap between the physical sciences of chemistry, physics, and geology, e.g., biochemistry, biophysics, and paleontology. Similarly there are those that relate to areas of human behavior, e.g., psychology and sociology.


Disciplines such as medicine, veterinary medicine, agronomy, and horticulture also have a strong basis in biology.


History of biology

To a large extent the history of biology is the history of its constituent sciences. Since the impetus to investigate the living world generally arose in a desire to improve the techniques of medicine or of agriculture, most early biologists were in the first instance physicians or landowners. An exception is provided by Aristotle, the earliest systematist of biological knowledge and himself an outstanding biologist – he founded the science of comparative anatomy – but most other classical authors, such as Galen and Celsus and the members of the Hippocratic school, were primarily physicians. In the medieval period much biological knowledge became entangled in legend and allegory. The classical texts continued to be the principal sources of knowledge although new compilations, such as Avicenna's Canon of medicine, were produced by Muslim philosophers. In sixteenth-century Europe interest revived in descriptive natural history, the work of Gesner being notable; physicians such as Paracelsus began to develop a chemical pharmacology and experimental anatomy revived in the work of Vesalius, Fabricius, and Fallopius. The discoveries of Servetus, Harvey, and Malpighi followed. Quantitative plant physiology began with the work of van Helmont and was taken to spectacular ends in the work of Stephen Hales. In the seventeenth century, microscopic investigations began with the work of Hooke and van Leeuwenhoek; Grew advanced the plant organs and Ray laid the foundation for Linnaeus' classic 18th-century formulation of the classification of plants. The same era saw Buffon devise a systematic classification of animals and von Haller lay the groundwork for the modern study of physiology.


The 17th century had seen controversies over the role of mechanism in biological explanation – la Mettrie had even developed the theories of Descartes to embrace the mind of man; the nineteenth century saw similar disputes, now couched in the form of the mechanist-vitalist controversy concerning the possible chemical nature of life (see Bichat, Bernard). Developmental biology, foreshadowed by Lamarck, was thoroughly established following the work of Darwin; in anatomy, Schwann and others developed the cell concept; in histology Bichat's pioneering work was continued; in physiology, organic and even physical chemists began to play a greater role, and medical theory was revolutionized by the advent of bacteriology (see Pasteur, Koch). The impact of Mendel's discoveries in genetics was not felt until the early 1900s. Possibly the high point of 20th-century biology came with the proposal of the double-helix model for DNA, the chemical carrier of genetic information, by Crick and Watson in 1953.