Although humans have always been interested in the natural history of the animals they saw around them, and used this knowledge to domesticate certain species, the formal study of zoology can be said to have originated withAristotle. He viewed animals as living organisms, studied their structure and development, and considered their adaptations to their surroundings and the function of their parts. Modern zoology has its origins during theRenaissance and early modern period, withCarl Linnaeus,Antonie van Leeuwenhoek,Robert Hooke,Charles Darwin,Gregor Mendel and many others.
The history of zoology traces the study of theanimal kingdom from ancient to modern times. Prehistoric people needed to study the animals and plants in their environment to exploit them and survive. Cave paintings, engravings and sculptures in France dating back 15,000 years show bison, horses, and deer in carefully rendered detail. Similar images from other parts of the world illustrated mostly the animals hunted for food and the savage animals.[3]
TheNeolithic Revolution, which is characterized by thedomestication of animals, continued throughout Antiquity. Ancient knowledge of wildlife is illustrated by the realistic depictions of wild and domestic animals in the Near East, Mesopotamia, and Egypt, including husbandry practices and techniques, hunting and fishing. The invention of writing is reflected in zoology by the presence of animals in Egyptian hieroglyphics.[4]
Although the concept ofzoology as a single coherent field arose much later, the zoological sciences emerged fromnatural history reaching back to thebiological works of Aristotle andGalen in the ancientGreco-Roman world. In the fourth century BC, Aristotle looked at animals as living organisms, studying their structure, development and vital phenomena. He divided them into two groups: animals with blood, equivalent to our concept ofvertebrates, and animals without blood,invertebrates. He spent two years onLesbos, observing and describing the animals and plants, considering the adaptations of different organisms and the function of their parts.[5] Four hundred years later, Roman physician Galen dissected animals to study their anatomy and the function of the different parts, because the dissection of human cadavers was prohibited at the time.[6] This resulted in some of his conclusions being false, but for many centuries it was consideredheretical to challenge any of his views, so the study of anatomy stultified.[7]
During thepost-classical era,Middle Eastern science and medicine was the most advanced in the world, integrating concepts from Ancient Greece, Rome, Mesopotamia and Persia as well as the ancient Indian tradition ofAyurveda, while making numerous advances and innovations.[8] In the 13th century,Albertus Magnus produced commentaries and paraphrases of all Aristotle's works; his books on topics likebotany, zoology, and minerals included information from ancient sources, but also the results of his own investigations. His general approach was surprisingly modern, and he wrote, "For it is [the task] of natural science not simply to accept what we are told but to inquire into the causes of natural things."[9] An early pioneer wasConrad Gessner, whose monumental 4,500-page encyclopedia of animals,Historia animalium, was published in four volumes between 1551 and 1558.[10]
In Europe, Galen's work on anatomy remained largely unsurpassed and unchallenged up until the 16th century.[11][12] During theRenaissance and early modern period, zoological thought was revolutionized inEurope by a renewed interest inempiricism and the discovery of many novel organisms. Prominent in this movement wereAndreas Vesalius andWilliam Harvey, who used experimentation and careful observation inphysiology, and naturalists such asCarl Linnaeus,Jean-Baptiste Lamarck, andBuffon who began toclassify the diversity of life and thefossil record, as well as studying the development and behavior of organisms.Antonie van Leeuwenhoek did pioneering work inmicroscopy and revealed the previously unknown world ofmicroorganisms, laying the groundwork forcell theory.[13] van Leeuwenhoek's observations were endorsed byRobert Hooke; all living organisms were composed of one or more cells and could not generate spontaneously. Cell theory provided a new perspective on the fundamental basis of life.[14]
Having previously been the realm of gentlemen naturalists, over the 18th, 19th and 20th centuries, zoology became an increasingly professionalscientific discipline. Explorer-naturalists such asAlexander von Humboldt investigated the interaction between organisms and their environment, and the ways this relationship depends on geography, laying the foundations forbiogeography,ecology andethology. Naturalists began to rejectessentialism and consider the importance ofextinction and themutability of species.[15]
These developments, as well as the results fromembryology andpaleontology, were synthesized in the 1859 publication ofCharles Darwin's theory ofevolution bynatural selection; in this Darwin placed the theory of organic evolution on a new footing, by explaining the processes by which it can occur, and providing observational evidence that it had done so.[16]Darwin's theory was rapidly accepted by the scientific community and soon became a central axiom of the rapidly developing science of biology. The basis for modern genetics began with the work ofGregor Mendel on peas in 1865, although the significance of his work was not realized at the time.[17]
Darwin gave a new direction tomorphology andphysiology, by uniting them in a common biological theory: the theory of organic evolution. The result was a reconstruction of the classification of animals upon agenealogical basis, fresh investigation of the development of animals, and early attempts to determine their genetic relationships. The end of the 19th century saw the fall ofspontaneous generation and the rise of thegerm theory of disease, though the mechanism ofinheritance remained a mystery. In the early 20th century, the rediscovery ofMendel's work led to the rapid development ofgenetics, and by the 1930s the combination ofpopulation genetics and natural selection in themodern synthesis createdevolutionary biology.[18]
Zoology is the branch of science dealing withanimals. Aspecies can be defined as the largest group of organisms in which any two individuals of the appropriate sex can produce fertile offspring; about 1.5 million species of animal have been described and it has been estimated that as many as 8 million animal species may exist.[21]An early necessity was to identify the organisms and group them according to their characteristics, differences and relationships, and this is the field of thetaxonomist. Originally it was thought that species were immutable, but with the arrival of Darwin's theory of evolution, the field ofcladistics came into being, studying the relationships between the different groups orclades.Systematics is the study of the diversification of living forms, the evolutionary history of a group is known as itsphylogeny, and the relationship between the clades can be shown diagrammatically in acladogram.[22]
Although someone who made a scientific study of animals would historically have described themselves as a zoologist, the term has come to refer to those who deal with individual animals, with others describing themselves more specifically as physiologists, ethologists, evolutionary biologists, ecologists, pharmacologists, endocrinologists or parasitologists.[23]
Although the study of animal life is ancient, its scientific incarnation is relatively modern. This mirrors the transition fromnatural history tobiology at the start of the 19th century. SinceHunter andCuvier, comparativeanatomical study has been associated withmorphography, shaping the modern areas of zoological investigation:anatomy,physiology,histology,embryology,teratology andethology.[24] Modern zoology first arose in German and British universities. In Britain,Thomas Henry Huxley was a prominent figure. His ideas were centered on themorphology of animals. Many consider him the greatest comparative anatomist of the latter half of the 19th century. Similar toHunter, his courses were composed of lectures and laboratory practical classes in contrast to the previous format of lectures only.
Linnaeus's table of the animal kingdom from the first edition ofSystema Naturae (1735)
Many scientists now consider thefive-kingdom system outdated. Modern alternative classification systems generally start with thethree-domain system:Archaea (originally Archaebacteria);Bacteria (originally Eubacteria);Eukaryota (includingprotists,fungi,plants, andanimals)[26] These domains reflect whether the cells have nuclei or not, as well as differences in the chemical composition of the cell exteriors.[26]
Further, each kingdom is broken down recursively until each species is separately classified. The order is:Domain;kingdom;phylum;class;order;family;genus;species. The scientific name of an organism is generated from its genus and species. For example, humans are listed asHomo sapiens.Homo is the genus, andsapiens the specific epithet, both of them combined make up the species name. When writing the scientific name of an organism, it is proper to capitalize the first letter in the genus and put all of the specific epithet in lowercase. Additionally, the entire term may be italicized or underlined.[27]
The dominant classification system is called theLinnaean taxonomy. It includes ranks andbinomial nomenclature. The classification,taxonomy, and nomenclature of zoological organisms is administered by theInternational Code of Zoological Nomenclature. A merging draft, BioCode, was published in 1997 in an attempt to standardize nomenclature, but has yet to be formally adopted.[28]
Cell biology studies the structural andphysiological properties ofcells, including theirbehavior, interactions, andenvironment. This is done on both themicroscopic andmolecular levels for single-celled organisms such asbacteria as well as the specialized cells inmulticellular organisms such ashumans. Understanding the structure and function of cells is fundamental to all of the biological sciences. The similarities and differences between cell types are particularly relevant to molecular biology.
Anatomy considers the forms of macroscopic structures such asorgans and organ systems.[29] It focuses on how organs and organ systems work together in the bodies of humans and other animals, in addition to how they work independently. Anatomy and cell biology are two studies that are closely related, and can be categorized under "structural" studies.Comparative anatomy is the study of similarities and differences in theanatomy of different groups. It is closely related toevolutionary biology andphylogeny (theevolution of species).[30]
Animal anatomical engraving fromHandbuch der Anatomie der Tiere für Künstler.
Physiology studies the mechanical, physical, and biochemical processes of living organisms by attempting to understand how all of the structures function as a whole. The theme of "structure to function" is central to biology. Physiological studies have traditionally been divided intoplant physiology andanimal physiology, but some principles of physiology are universal, no matter what particularorganism is being studied. For example, what is learned about the physiology ofyeast cells can also apply to human cells. The field of animal physiology extends the tools and methods ofhuman physiology to non-human species. Physiology studies how, for example, thenervous,immune,endocrine,respiratory, andcirculatory systems function and interact.[31]
Evolutionary biology is the subfield of biology that studies the evolutionary processes (natural selection, common descent, speciation) that produced the diversity of life on Earth. Evolutionary research is concerned with the origin and descent ofspecies, as well as their change over time, and includes scientists from manytaxonomically oriented disciplines. For example, it generally involves scientists who have special training in particularorganisms such asmammalogy,ornithology,herpetology, orentomology, but use those organisms as systems to answer general questions about evolution.[33]
Evolutionary biology is partly based onpaleontology, which uses thefossil record to answer questions about the mode and tempo of evolution,[34] and partly on the developments in areas such aspopulation genetics[35] and evolutionary theory. Following the development ofDNA fingerprinting techniques in the late 20th century, the application of these techniques in zoology has increased the understanding of animal populations.[36] In the 1980s,developmental biology re-entered evolutionary biology from its initial exclusion from themodern synthesis through the study ofevolutionary developmental biology. Related fields often considered part of evolutionary biology arephylogenetics,systematics, andtaxonomy.[37]
Kelp gull chicks peck at red spot on mother's beak to stimulate the regurgitating reflex.
Ethology is thescientific and objective study of animal behavior under natural conditions,[38] as opposed tobehaviorism, which focuses on behavioral response studies in a laboratory setting. Ethologists have been particularly concerned with theevolution of behavior and the understanding of behavior in terms of the theory ofnatural selection. In one sense, the first modern ethologist wasCharles Darwin, whose book,The Expression of the Emotions in Man and Animals, influenced many future ethologists.[39]
A clade representation of seven dog breeds in relation to wolves.
Molecular biology studies the commongenetic and developmental mechanisms of animals and plants, attempting to answer the questions regarding the mechanisms ofgenetic inheritance and the structure of thegene. In 1953,James Watson andFrancis Crick described the structure of DNA and the interactions within the molecule, and this publication jump-started research into molecular biology and increased interest in the subject.[45] While researchers practice techniques specific to molecular biology, it is common to combine these with methods fromgenetics andbiochemistry. Much of molecular biology is quantitative, and recently a significant amount of work has been done usingcomputer science techniques such asbioinformatics andcomputational biology.
Molecular genetics, the study of gene structure and function, has been among the most prominent sub-fields of molecular biology since the early 2000s. Other branches of biology are informed by molecular biology, by either directly studying the interactions of molecules in their own right such as incell biology anddevelopmental biology, or indirectly, where molecular techniques are used to infer historical attributes ofpopulations orspecies, as in fields inevolutionary biology such aspopulation genetics andphylogenetics. There is also a long tradition of studyingbiomolecules "from the ground up", or molecularly, inbiophysics.[46]
Animals generally reproduce bysexual reproduction, a process involving the union of a male and femalehaploidgamete, each gamete formed bymeiosis. Ordinarily, gametes produced by separate individuals unite by a process of fertilization to form a diploidzygote that can then develop into a genetically unique individual progeny. However, some animals are also capable, as an alternative reproductive process, to reproduce parthenogenetically. Parthenogenesis has been described in snakes and lizards (see WikipediaParthenogenesis in squamates), in amphibians (see WikipediaParthenogenesis in amphibians) and in numerous other species (see WikipediaParthenogenesis). Generally, meiosis in parthanogenetically reproducing animals occurs by a similar process to that in sexually reproducing animals, but the diploid zygote nucleus is generated by the union of two haploid genomes from the same individual rather than from different individuals.
^Claudii Galeni Pergameni (1992). Odysseas Hatzopoulos (ed.)."That the best physician is also a philosopher" with a Modern Greek Translation.Athens,Greece: Odysseas Hatzopoulos & Company: Kaktos Editions.
^Friedman, Meyer; Friedland, Gerald W. (1998).Medecine's 10 Greatest Discoveries. Yale University Press. p. 2.ISBN0-300-07598-7.
^Bayrakdar, Mehmet (1986). "Al-Jahiz and the rise of biological evolution".Ankara Üniversitesi İlahiyat Fakültesi Dergisi.27 (1).Ankara University:307–315.doi:10.1501/Ilhfak_0000000674 (inactive 1 November 2024).{{cite journal}}: CS1 maint: DOI inactive as of November 2024 (link)
^Wyckoff, Dorothy (1967).Book of Minerals. Oxford: Clarendon Press. pp. Preface.
^Scott, Michon (26 March 2017)."Conrad Gesner".Strange Science: The rocky road to modern paleontology and biology.Archived from the original on 2021-06-16. Retrieved2017-09-27.
^John McNeill (4 November 1996). "The BioCode: Integrated biological nomenclature for the 21st century?".Proceedings of a Mini-Symposium on Biological Nomenclature in the 21st Century.
^Vassiliki Betty Smocovitis (1996).Unifying Biology: The Evolutionary Synthesis and Evolutionary Biology. Princeton University Press.ISBN978-0-691-03343-3.
^"Definition of Ethology".Merriam-Webster.Archived from the original on 2009-04-25. Retrieved2012-10-30.2 : the scientific and objective study of animal behaviour especially under natural conditions
^Browne, Janet (1983).The secular ark: studies in the history of biogeography. New Haven: Yale University Press.ISBN978-0-300-02460-9.
^Tabery, James; Piotrowska, Monika; Darden, Lindley (19 February 2005)."Molecular Biology (Fall 2019 Edition)". In Zalta, Edward N. (ed.).The Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University.Archived from the original on 2024-06-12. Retrieved2020-04-19.
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