Zoology
Branch of biology concerned with members of the animal kingdom and with animal life in general. The science originated in the works of Hippocrates, Aristotle, and Pliny. The contributions of individuals such as William Harvey (the circulation of blood), Carolus Linnaeus (system of nomenclature), Georges-Louis de Buffon (natural history), Georges Cuvier (comparative anatomy), and Claude Bernard (homeostasis) greatly advanced the field. The 1859 publication of Charles Darwin's On the Origin of Species by Means of Natural Selection was a major turning point. Since that time, the study of genetics has become essential in zoological studies.
The science that deals with knowledge of animal life. With the great growth of information about animals, zoology has been much subdivided. Some major fields are anatomy, which deals with gross and microscopic structure; physiology, with living processes in animals; embryology, with development of new individuals; genetics, with heredity and variation; parasitology, with animals living in or on others; natural history, with life and behavior in nature; ecology, with the relation of animals to their environments; evolution, with the origin and differentiation of animal life; and taxonomy, with the classification of animals. See also Anatomy, regional; Developmental biology; Genetics; Parasitology; Phylogeny; Plant evolution.
Zoology is the area of systematic biology that studies the animal kingdom. Systematic biology (or just systematics) is "the scientific study of the kinds and diversity of organisms" (Simpson, p. 7). The animal kingdom is one of at least five kingdoms into which organisms are now divided; the others are plants, fungi, protoctists, and bacteria. The last two kingdoms comprise only unicellular organisms: protoctists include all unicellular organisms formerly considered animals, among them amoebas and paramecia, as well as several types of unicellular algae; bacteria are unicellular organisms lacking a differentiated cellular nucleus. Animals and plants are multicellular organisms, but plants have cell walls and animals do not. Fungi may be unicellular or multicellular, but do not develop through embryological stages, as do plants and animals. Therefore, animals may be loosely defined as multicellular organisms that lack cell walls, but develop through embryological stages.
Zoology is divided into different fields: Mammalogy (the study of mammals), Ornithology (birds), Herpetology (reptiles and amphibians), ichthyology (fish), entomology (insects), malacology (mollusks, from snails with and without shells to squids and octopuses), and helmintology (worms, from earthworms to flatworms), among others. Zoologists usually specialize in the study of only one group or of closely related groups of animals. If a zoologist specializes in extinct animals, of which only fossil remains are known, he is called a paleozoologist (the term paleontologist includes the paleobotanists, who study plant fossils). Zoogeography is a special field of zoology that studies the geographical distribution of animals and is closely linked with research on the evolution of animal species.