(the scientific study of animals)
Zoology is the study of animals
It is a subdivision of biology, which is the study of all living things. Zoology encompasses all aspects, from the molecular level, to the organ, to that of the whole animal, and from unicellular organisms to whales. There are many subdisciplines of zoology (e.g., genetics, biochemistry, parasitology, physiology, ethology, ecology, systematics, ichthyology, ornithology, mammology, and so on), with further subdivisions (e.g., physiological ecology, neurophysiology, respiratory physiology, etc.).
Initial studies of zoology concentrated on describing the anatomy and categorizing animals (systematics), and this goes on today. Not all animals are named and described (especially insects), and there is a continuing argument as to the most appropriate grouping (classification) of animals.
More recently, interest has developed into the molecular aspects of zoology, made possible by techniques developed in chemistry and physics but applied to biological systems. There are many similarities at the molecular level between animals and plants, and consequently the subject is usually referred to as Molecular Biology rather than Molecular Zoology or Botany.
Historical origins of zoological classifications
The earliest known system of zoological classification is that of Aristotle, who attempted in the 4th century B.C. to group animals according to such criteria as mode of reproduction and possession or lack of red blood.
Aristotle's pupil, Theophrastus, classified plants according to their uses and methods of cultivation. Little interest was shown in classification until the 17th and 18th centuries, when botanists and zoologists started to devise the modern scheme of categories. The designation of groups was based almost entirely on superficial anatomical resemblances.
Before the idea of evolution, there was no push to show more meaningful relationships among species because the species was thought to be uniquely created and fixed in character, the only real, or natural, taxon, while the higher taxa were only regarded as an artificial means of organizing information.
Since anatomical resemblance is an important indication of relationship, early classification efforts resulted in a system that often approximated a natural one and that is still the system that is used with considerable modifications. The most extensive work was done in the mid-18th century by Carolus Linnaeus, who devised the presently used system of nomenclature.
As biologists came to accept the work of Charles Darwin in the second half of the 19th century, they started to stress the significance of evolutionary relationships for classifications.
Although comparative anatomy remained important, other evidence of relationship was sought as well. Paleontology provided fossil evidence of the common ancestry of various groups; embryology provided comparisons of early development in different species, an important clue to their relationships.
In the 20th century, evidence provided by genetics and physiology became increasingly important. Recently there has been much emphasis on the use of molecular genetics in taxonomy, as in the comparison of nucleic acid sequences in the genetic makeup of organisms. Computers are increasingly used to analyze data relevant to taxonomy.