Zoology

Attempts at animal classification are known from documents in the collection of the Greek physician Hippocrates, as early as 400 Before the Common Era (BCE). However, the Greek philosopher Aristotle (384-322 BCE) was the first to devise a system of classifying animals that recognized commonalities among diverse organisms. Aristotle arranged groups of animals according to mode of reproduction and habitat. After observing the development of selected animal groups, he noted that general structures appear before specialized ones, and he also distinguished between sexual and asexual reproduction. Aristotle was also interested in form and structure and concluded that different animals can have similar embryological origins, and different structures can have similar functions.

In Roman times, Pliny the Elder (23-79 Common Era [CE]) compiled four volumes on zoology, widely read during the Middle Ages. Some scholars have deemed those volumes little more than a collection of folklore, myth, and superstition. One of the more influential figures in the history of physiology, the Greek physician Galen (c. 130-c. 201 CE), dissected farm animals, monkeys, and other mammals and described many features accurately. However, scholars have noted that some of these features were then wrongly applied to the human body. His misconceptions, especially concerning the movement of blood, remained virtually unchanged for hundreds of years. In the seventeenth century, the English physician William Harvey established the true mechanism of blood circulation.

The Foundations of Zoology

Until the Middle Ages, zoology was little more than a collection of folklore and superstition. However, zoology began to emerge as a science during the twelfth century. The thirteenth-century German scholar and naturalist St. Albertus Magnus refuted many of the superstitions associated with biology and reintroduced the work of Aristotle. The anatomical studies of Leonardo da Vinci in the fifteenth century have been noted as being far ahead of their time. His dissections and comparisons of the structure of humans and other animals led him to several important conclusions. For example, Leonardo noted that the arrangement of joints and bones in the leg are similar in both horses and humans, thus embracing the concept of homology, or the similarity of corresponding parts in different kinds of animals, suggesting a common grouping. A Flemish physician of the sixteenth century, Andreas Vesalius, is considered the father of anatomy for establishing the principles of comparative anatomy.

Throughout most of the seventeenth and eighteenth centuries, classification dominated zoology. The Swedish botanistCarolus Linnaeus developed a system of nomenclature that is still in use today, referred to as the binomial system of genus and species. Linnaeus also established taxonomy as a discipline. His work was built on the work of the English naturalist John Ray and relied upon the form of teeth and toes to differentiate mammals and upon beak shape to classify birds. Another leading figure in the systematic development of this era was the French biologist Comte Georges-Louis Leclerc de Buffon. The study of comparative anatomy was further developed by men such as Georges Cuvier, who devised a systematic organization of animals based on specimens sent to him from all over the world.

A cell is the smallest structural unit of an organism capable of independent functioning. Although the word “cell” was introduced in the seventeenth century by the English scientist Robert Hooke, it was not until 1839 that two Germans, Matthias Schleiden and Theodor Schwann, proved that the cell is the common structural unit of living things. The concept of the cell provided the impetus for progress in embryology and animal physiology, including the concept of homeostasis, referring to the stability of the body’s internal environment.

The formation of scientific expeditions in the eighteenth and nineteenth centuries allowed scientists to study plant and animal life worldwide. The most famous scientific expedition was the voyage of the HMS Beagle in the early 1830s. During this voyage, Charles Darwin observed the plant and animal life of South America and Australia and developed his theory of evolution by natural selection. Although Darwin recognized the importance of heredity in understanding the evolutionary process, he was unaware of the work of a contemporary, the Austrian monk Gregor Mendel, who first formulated the concept of particulate hereditary factors, later called genes. Mendel’s work was not widely disseminated until 1900.

Modern Zoology

During the twentieth century, zoology became more diversified and less confined to such traditional issues as classification and anatomy. Zoology, broadening its span to include such areas of study as genetics, ecology, and biochemistry, became an interdisciplinary field applying various techniques to obtain knowledge about the animal kingdom. The study of zoology at the end of the twentieth century focused on taxonomic groups and the structures and processes common to these groups. This work continued into the twenty-first century as well. Studies of taxonomy concentrate on the different divisions of animal life. Invertebrate zoology deals with multicellular animals without backbones; its subdivisions include entomology (the study of insects) and malacology (the study of mollusks). Vertebrate zoology, the study of animals with backbones, is divided into ichthyology (the study of fish), herpetology (amphibians and reptiles), ornithology (birds), and mammalogy (mammals). Taxonomic groups also subdivide paleontology, the study of fossils. In each field, researchers investigate the classification, distribution, life cycle, and evolutionary history of the particular animal or group of animals under study. Most zoologists are also specialists in one or more of the related disciplines of morphology, physiology, embryology, and ecology.

Animal behavioral studies have developed along two lines. The first of these, animal psychology, is primarily concerned with physiological psychology and has traditionally concentrated on laboratory techniques such as conditioning. The second, ethology, originated in observing animals under natural conditions, concentrating on courtship, flocking, and other social contacts. One of the important recent developments in the field is the focus on sociobiology, concerned with the behavior, ecology, and evolution of social animals such as bees, ants, schooling fish, flocking birds, and humans. Careers in zoology continue to expand, as does the science behind studying animals. As more discoveries were made in the twenty-first century, zoology and its specializations grew.

As the twenty-first century progressed, technological developments, a focus on conservation, and increased interdisciplinary collaboration influenced zoology. Artificial intelligence (AI) has enhanced the ability of zoologists to collect and interpret data. AI has also allowed zoologists to monitor animals using a noninvasive approach, allowing for more comprehensive study. Using remote sensing technology like drones has allowed zoologists to increasingly monitor animal behavior within their native habitats. Advances have also been made in the field of zoological medicine, allowing for the better care of animals in the wild and captive habitats. Zoologists have become integral in wildlife conservation efforts, which have received increased attention due to global climate change. Finally, with these advances come new opportunities for careers in zoology, especially in areas combining zoology and technology. 

Principal Terms

Comparative Anatomy: the branch of natural science dealing with the structural organization of living things

Ecology: the study of the interactions between animals and their environment

Embryology: the study of the development of individual animals

Evolutionary Zoology: the study of the mechanisms of evolutionary change and the evolutionary history of animal groups

Morphology: the study of structure; includes gross morphology, which examines entire structures or systems, such as muscles or bones; histology, which examines body tissues; and cytology, which focuses on cells and their components

Phylogenetics: the study of the developmental history of groups of animals

Physiology: the study of the functions, activities, and processes of living organisms

Systematics: the delineation and description of animal species and their arrangement into a classification

Taxonomy: the classification of organisms in an ordered system that indicates natural relationships

Zoogeography: the study of the distribution of animals over the Earth

Bibliography

Allaby, Michael, editor. The Concise Oxford Dictionary of Zoology. 2d ed. New York: Oxford University Press, 1999.

Anderson, Donald Thomas. Invertebrate Zoology. New York: Oxford University Press, 1999.

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Griffin, Donald R. Animal Minds. Chicago: University of Chicago Press, 1992.

Proctor, Noble S., and Patrick J. Lynch. Manual of Ornithology: Avian Structure and Function. New Haven, Conn.: Yale University Press, 1993.

Taylor, Barbara. Animal Encyclopedia. New York: Dorling Kindersley, 2000.

Wernert, Susan J., editor. Reader’s Digest North American Wildlife: An Illustrated Guide to Two Thousand Plants and Animals. Pleasantville, N.Y.: Reader’s Digest Association, 1998.

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Wilson, Edward O. Sociobiology: The New Synthesis. Cambridge, Mass.: The Belknap Press of Harvard University Press, 2000.

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