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Zoology

Zoology

Zoology (Greek zoon = animal and logos = word) is the biological discipline which involves the study of animals.

History of zoology

Main articles: History of zoology (before Darwin), History of zoology (since Darwin)

Branches of biology relevant to zoology

The original branches of zoology established in the late 19th century such as zoo-physics, bionomics and morphography, have largely been subsumed into more broad areas of biology which include studies of mechanisms common to both plants and animals. The biology of animals is covered in several broad areas: #The physiology of animals is studied under various fields including anatomy and embryology #The common genetic and developmental mechanisms of animals and plants is studied in molecular biology, molecular genetics and developmental biology #The ecology of animals is covered under behavioral ecology and other fields #Evolutionary biology of both animals and plants is considered in the articles on evolution, population genetics, heredity, variation, Mendelism, reproduction. #Systematics, cladistics, phylogenetics, phylogeography, biogeography and taxonomy classify and group species via common descent and regional associations. In addition the various taxonomically oriented-disciplines such as mammalogy, herpetology, ornithology study mechanisms that are specific to those groups.

Systems of classification

Main article: Scientific classification Morphography includes the systematic exploration and tabulation of the facts involved in the recognition of all the recent and extinct kinds of animals and their distribution in space and time. (1) The museum-makers of old days and their modern representatives the curators and describers of zoological collections, (2) early explorers and modern naturalist travellers and writers on zoo-geography, and (3) collectors of fossils and palaeontologists are the chief varieties of zoological workers coming under this heading. Gradually, since the time of Hunter and Cuvier, anatomical study has associated itself with the more superficial morphography until today no one considers a study of animal form of any value which does not include internal structure, histology and embryology in its scope. The real dawn of zoology after the legendary period of the Middle Ages is connected with the name of an Englishman, Edward Edward Wotton, born at Oxford in 1492, who practised as a physician in London and died in 1555. He published a treatise De differentiis animalium at Paris in 1552. In many respects Wotton was simply an exponent of Aristotle, whose teaching, - with various fanciful additions, constituted the real basis of zoological knowledge throughout the Middle Ages. It was Wotton's merit that he rejected the legendary and fantastic accretions, and returned to Aristotle and the observation of nature. The most ready means of noting the progress of zoology during the 16th, 17th and 18th centuries is to compare Aristotle's classificatory conceptions of successive naturalists with those which are to be found in the works of Caldon.

Notable zoologists

- Louis Agassiz (malacology, ichthyology)
- Aristotle
- Archie Carr, (June 16, 1909-May 21, 1987) (Herpetology), esp. sea turtles
- Charles Darwin
- Dian Fossey (primatology)
- Arthur David Hasler, (January 5, 1908-March 23, 2001) (limnology, ichthyology, salmon homing)
- Victor Hensen, (February 10, 1835-April 5, 1924) (planktology)
- Libbie Hyman (invertebrate zoology)
- William Kirby (father of entomology)
- Carolus Linnaeus (father of systematics)
- Konrad Lorenz (ethology)
- David W. Macdonald (wild mammals)
- Ernst Mayr (1905-2005), influential evolutionary biologist, one of the founders of the "modern synthesis" of evolutionary theory in the 1940s.
- Desmond Morris (ethology)
- Ron Nowak (wild mammals)
- Roger Tory Peterson (ornithology)
- Thomas Say (entomology)
- Ernest P. Walker (wild mammals)
- E. O Wilson, b. 1929, (entomology, founder of sociobiology)
- Jakob van Uexküll (animal behavior, invertebrate zoology)

Greek language

Greek (Greek Ελληνικά, IPA – "Hellenic") is an Indo-European language with a documented history of 3,500 years. Today, it is spoken by 15 million people in Greece, Cyprus, the former Yugoslavia, particularly The Former Yugoslav Republic of Macedonia, Bulgaria, Albania and Turkey. There are also many Greek emigrant communities around the world, such as those in Melbourne, Australia which is the third-largest Greek-populated city in the world, after Athens and Thessaloniki. Greek has been written in the Greek alphabet, the first true alphabet, since the 9th century B.C. and before that, in Linear B and the Cypriot syllabaries. Greek literature has a long and rich tradition.

History

This article does not cover the reconstructed history of Greek prior to the use of writing. For more information, see main article on Proto-Greek language. Greek has been spoken in the Balkan Peninsula since the 2nd millennium BC. The earliest evidence of this is found in the Linear B tablets dating from 1500 BC. The later Greek alphabet (q.v.) is unrelated to Linear B, and was derived from the Phoenician alphabet (abjad); with minor modifications, it is still used today. Greek is conventionally divided into the following periods:
- Mycenean Greek: the language of the Mycenean civilisation. It is recorded in the Linear B script on tablets dating from the 16th century BC onwards.
- Classical Greek (also known as Ancient Greek): In its various dialects was the language of the Archaic and Classical periods of Greek civilisation. It was widely known throughout the Roman empire. Classical Greek fell into disuse in western Europe in the Middle Ages, but remained known in the Byzantine world, and was reintroduced to the rest of Europe with the Fall of Constantinople and Greek migration to Italy.
- Hellenistic Greek (also known as Koine Greek): The fusion of various ancient Greek dialects with Attic (the dialect of Athens) resulted in the creation of the first common Greek dialect, which gradually turned into one of the world's first international languages. Koine Greek can be initially traced within the armies and conquered territories of Alexander the Great, but after the Hellenistic colonisation of the known world, it was spoken from Egypt to the fringes of India. After the Roman conquest of Greece, an unofficial diglossy of Greek and Latin was established in the city of Rome and Koine Greek became a first or second language in the Roman Empire. Through Koine Greek it is also traced the origin of Christianity, as the Apostles used it to preach in Greece and the Greek-speaking world. It is also known as the Alexandrian dialect, Post-Classical Greek or even New Testament Greek (after its most famous work of literature).
- Medieval Greek: The continuation of Hellenistic Greek during medieval Greek history as the official and vernacular (if not the literary nor the ecclesiastic) language of the Byzantine Empire, and continued to be used until, and after the fall of that Empire in the 15th century. Also known as Byzantine Greek.
- Modern Greek: Stemming independently from Koine Greek, Modern Greek usages can be traced in the late Byzantine period (as early as 11th century). Two main forms of the language have been in use since the end of the medieval Greek period: Dhimotikí (Δημοτική), the Demotic (vernacular) language, and Katharévousa (Καθαρεύουσα), an imitation of classical Greek, which was used for literary, juridic, and scientific purposes during the 19th and early 20th centuries. Demotic Greek is now the official language of the modern Greek state, and the most widely spoken by Greeks today. It has been claimed that an "educated" speaker of the modern language can understand an ancient text, but this is surely as much a function of education as of the similarity of the languages. Still, Koinē , the version of Greek used to write the New Testament and the Septuagint, is relatively easy to understand for modern speakers. Greek words have been widely borrowed into the European languages: astronomy, democracy, philosophy, thespian, etc. Moreover, Greek words and word elements continue to be productive as a basis for coinages: anthropology, photography, isomer, biomechanics etc. and form, with Latin words, the foundation of international scientific and technical vocabulary. See English words of Greek origin, and List of Greek words with English derivatives.

Classification

Greek is an independent branch of the Indo-European language family. The ancient languages which were probably most closely related to it, Ancient Macedonian language (which may be regarded as a dialect of Greek) and Phrygian, are not well enough documented to permit detailed comparison. Among living languages, Armenian seems to be the most closely related to it.

Geographic distribution

Modern Greek is spoken by about 15 million people mainly in Greece and Cyprus. There are also Greek-speaking populations in Georgia, Ukraine, Egypt, Turkey, Albania, Former Yugoslav Republic of Macedonia and Southern Italy. The language is spoken also in many other countries where Greeks have settled, including Armenia, Australia, Austria, Belgium, Bulgaria, Canada, Denmark, France, Germany, Netherlands, Sweden, United Kingdom, and the United States.

Official status

Greek is the official language of Greece where it is spoken by about 99.5% of the population. It is also, alongside Turkish, the official language of Cyprus. Due to the membership of Greece and Cyprus, Greek is one of the 20 official languages of the European Union.

Phonology

This section generally describes the post-Classic phonology of the Greek language. :All phonetic transcriptions in this section use the International Phonetic Alphabet

Vowel sounds

Greek has 5 vowel sounds, all phonemic:

Academic discipline

This is a list of academic disciplines (and academic fields). An academic discipline is a branch of knowledge which is formally taught, either at the university, or via some other such method. Functionally, disciplines are usually defined and recognised by the academic journals in which research is published, and the learned societies to which their practitioners belong. Each discipline usually has several sub-disciplines or branches and distinguishing lines are often both arbitrary and ambiguous. Historically (in medieval Europe) there where only four faculties in a university: Theology, Medicine, Jurisprudence and Arts, with the last one having a somewhat lower status than the other three. Today's disciplines have their roots in the mid- to late-19th century secularization of universities, when the traditional curriculum was supplemented by non-classical languages and literatures, physics, chemistry, biology, and engineering. In the opening decades of the 20th century, education, sociology, and psychology took their place in the university curriculum. A "
- " denotes a field whose academic status is debated.

Natural sciences

Astronomy

- Astrophysics
- Cosmogony
- Cosmology

Behavioral science

Mathematics and computer science

Mathematics

- Algebra
- Analysis
- Calculus
- Game theory
- Geometry
- Information theory
- Number theory
- Probability theory
- Statistics
- Topology
- For a more extensive list, see list of mathematical topics, and list of lists of mathematical topics.

Computer science

- Algorithms
- Artificial intelligence
- Computer security
- Computing
- Complexity theory
- Cryptography
- Distributed systems
- Hardware
- Programming (see List of programming languages)
- Formal methods
- Information systems
- Robotics
- Visual Analytics See also: ACM [http://www.acm.org/class/ Computing Classification System]

Social sciences

Anthropology

- Biological anthropology
- Primate behavior
- Human evolution
- Population genetics
- Forensic anthropology
- Anthropological linguistics
- Synchronic linguistics (or Descriptive linguistics)
- Diachronic linguistics (or Historical linguistics)
- Educational
- Ethnolinguistics
- Sociolinguistics
- Archeology
- Cultural anthropology
- Anthropology of religion
- Anthropology of technology
- Economic anthropology
- Ethnography
- Ethnohistory
- Ethnology
- Ethnomusicology
- Human behavioral ecology
- Mythology
- Political anthropology
- Psychological anthropology
- Urban anthropology
- Historical anthropology

Archaeology

Communications

- Animal communications
- Information theory
- Interpersonal communications
- Marketing
- Propaganda
- Public affairs
- Public diplomacy
- Public relations
- Technical Writing
- Nonverbal communications
- Speech communications
- Telecommunications
- Computer-mediated communications
- Telecommunications Systems Management

Economics

- Econometrics
- Game theory
- Human development theory
- Labour economics
- Microeconomics
- Macroeconomics

Ethnic Studies

- Asian American Studies
- Black Studies or African American Studies
- Latino/Latina Studies
- Native American Studies

Ethnology

- Ethnomusicology
- Folklore

History

- Ancient history
- Diplomatic history
- European history
- Military history
- Modern history

Geography

- Cultural geography
- Economic geography
- Environmental geography
- Human geography
- Physical geography

Linguistics

- Historical linguistics
- Interlinguistics
- Morphology
- Phonetics
- Phonology
- Semantics
- Sociolinguistics
- Syntax

Political science

- Civics
- International relations
- Political philosophy
- Psephology
- Public policy

Psychology

- Astropsychology
-
- Behavioural psychology
- Cognitive psychology
- Cognitive science
- Differential psychology
- Developmental psychology
- Evolutionary psychology
- Experimental psychology
- Intrapersonal communications
- Neuropsychology
- Organisational psychology
- Psychology of work
- Parapsychology
-
- Psychoanalysis
- Social psychology

Semiotics

- Vexillology
-

Sociology

- Collective behavior
- Computational sociology
- Environmental sociology
- Interactionism
- Economic development
- Economic sociology
- Feminist sociology
- Functionalism
- Future studies
- Human ecology
- Industrial sociology
- Media Sociology
- Medical sociology
- Political sociology
- Program evaluation
- Public sociology
- Pure sociology
- Rural Sociology
- Science studies
- Science and technology studies
- Social change
- Social demography
- Social inequality
- Social movements
- Social Theory
- Sociology of culture
- Sociology of conflict
- Sociology of deviance
- Sociology of disaster
- Sociology of the family
- Sociology of markets
- Sociology of religion
- Sociology of sport
- Urban studies or Urban sociology
- Visual sociology

Humanities and arts

Area studies (sometimes called cultural studies)

- American studies
- African studies
- Asian Studies
- Catholic studies
- Chinese studies
- Eastern European studies
- Esperanto studies
- German studies
- International Studies
- Japanese studies
- Latin American studies
- Irish studies
- Islamic studies
- Jewish studies
- Russian studies

Art

- Art history
- Studio art

Classics

Creative writing

- Poetry composition
- Fiction writing
- Non-fiction writing and literary journalism

Dance

- Choreography
- Dance analysis
- Dance notation
- Dance studies
- Ethnochoreology
- History of dance
- Performance, somatic practice

English literature

also see Literature
- American literature
- African American literature
- Southern literature
- Australian literature
- British literature (literature outside England may be written in Celtic languages)
- English literature
- Northern Ireland literature
- Scottish literature
- Welsh literature
- Canadian literature (a significant amount of Canadian literature is also written in French)
- Irish literature
- New Zealand literature

Film studies and film criticism

- Animation

Folklore

History

- Ancient history
- Diplomatic history
- Ethnohistory
- European history
- History of science and technology
- Military history
- Modern history

Linguistics

see entry under social sciences

Literature and cultural studies

- English studies
- Comparative literature

Literatures

- English literature
- African American literature
- American literature
- British literature
- Indian literature
- Irish literature
- French literature
- Gaelic literature
- German literature
- Hindi literature
- Modern Hebrew Literature
- Portuguese & Brazilian literature
- Spanish literature
- Yiddish literature
- other languages' and cultures' literatures

Methods and topics

- Literary criticism
- Literary theory
- Media studies
- New media
- Poetics

Music

- Accompanying
- Arts leadership
- Chamber music
- Church music
- Musical composition
- Conducting
- Choral conducting
- Orchestral conducting
- Wind ensemble conducting
- Early music
- Jazz studies and new media
- Music education
- Music theory pedagodgy
- Music history
- Music theory
- Musicology
- Ethnomusicology
- Performance and literature
- Organ and historical keyboards
- Piano
- Strings, harp, and guitar
- Voice
- Woodwinds, brass, and percussion
- Orchestral studies

Museology

Mythology

Philology

Philosophy

- Aesthetics
- Continental philosophy
- Eastern philosophy
- Epistemology
- Ethics
- Hermeneutics
- History of philosophy
- Logic
- Metaphysics
- Philosophy of language
- Philosophy of mathematics
- Philosophy of mind
- Philosophy of religion
- Philosophy of science

Religious studies

- Canon law
- Catholic studies
- Comparative religious studies
- Islamic studies
- Hadith
- Islamic history
- Islamic jurisprudence
- Qur'an
- Jewish Studies
- Bible
- Halacha
- Jewish history
- Jewish philosophy
- Jewish literature
- Mythology
- Theology
- Astrology
-
- Christology
- Kabbalah
- Midrash
- Moral theology
- Mystical theology
- Numerology
-
- Spirituality
- Talmud

Theatre

- History
- Acting
- Directing
- Design
- Dramaturgy

Women's studies and gender studies

- Queer studies

Professions / Applied sciences

Design

- city planning, urban planning
- industrial design, product design
- graphic design
- architecture
- interior design (also see family and consumer science below)
- landscape architecture

Business

- Accounting scholarship
- Business ethics
- Finance
- Industrial and labor relations
- Collective bargaining
- Human resources
- Organizational Behavior
- International and comparative labor
- Labor economics
- Labor history
- Labor statistics
- Information systems
- Management
- Marketing
- Manufacturing

Education

- Curriculum and instruction
- Elementary Education (Primary education & Intermediate education)
- Middle school education
- Secondary education
- Higher education
- Physical Education
- Educational administration
- Educational psychology
- Educational technology

Engineering

- Acoustic engineering
- Agricultural engineering
- Architectural engineering
- Bioengineering
- Biomaterials engineering
- Biomedical engineering
- Chemical engineering
- Civil engineering
- Combat engineering
- Computer engineering
- Control systems engineering
- Electrical engineering
- Electronic engineering
- Microelectronics and semiconductor engineering
- Environmental engineering
- Industrial engineering
- Materials engineering
- Ceramic engineering
- Metallurgical engineering
- Polymer engineering
- Mechanical engineering
- Mining engineering
- Nuclear engineering
- Ocean engineering
- Optical engineering
- Quality assurance engineering
- Petroleum engineering
- Robotics
- Safety engineering
- Telecommunications engineering
- Transportation engineering
- Aerospace engineering
- Automotive systems engineering
- Naval engineering
- Marine engineering
- Naval architecture

Ergonomics

Agriculture

- Animal science
- Agrology
- Agricultural economics
- Aquaculture
- Beekeeping (Apiculture)
- Horticulture
- Plant science

Forestry

- Forestry organisation
- Silviculture

Family and consumer science

- Foodservice management
- Hotel administration
- Consumer education
- Housing
- Interior design (also see architecture and environmental design above)
- Nutrition (also see medical sciences below)
- Textiles

Journalism and mass communications

- Advertising
- Film
- Journalism
- Broadcast journalism
- New media journalism
- Print journalism
- Public relations
- List of journalists

Law

- Canon law
- Comparative law
- Constitutional law
- Civil law
- Accounting law
- Admiralty law
- Corporations
- Civil procedure
- Contracts
- Environmental law
- International law
- Labor law
- Property law
- Tax law
- Torts
- Criminal law
- Criminal procedure
- Criminal justice (also see Public Affairs and Community Service below)
- Police science
- Forensics
- Islamic law
- Jewish law
- Jurisprudence
- Philosophy of law

Library and information science

Health sciences

- Medical Sciences
- Dentistry
- Dental hygiene and Epidemiology
- Dental surgery
- Restorative dentistry and Endodontics
- Orthodontics
- Oral and maxillofacial surgery
- Pedodontics (Pediatric dentistry)
- Periodontics
- Prosthodontics
- Implantology
- Human medicine
- Cardiology
- Endocrinology and diabetology
- Epidemiology
- Forensics
- Geriatrics
- Hematology
- Internal medicine
- Health science
- Nephrology
- Neurology
- Neurosurgery
- Pathology
- Pediatrics
- Psychiatry (see also: Anti-psychiatry
- )
- Rheumatology
- Surgery
- Midwifery
- Nursing
- Veterinary medicine
- Nutrition (also see family and consumer science above)
- Optometry
- Pharmacy
- Physiotherapy
- Public health

Military science

- Artillery
- Air force studies
- Campaigning
- Combat engineering
- Comparative military systems
- Doctrine
- Force planning
- Game theory (also see economics above)
- Generalship
- Joint warfare studies
- Leadership
- Logistics
- Military ethics
- Military history
- Military intelligence
- Military law
- Military medicine
- Naval science
- Naval engineering
- Naval tactics
- Naval architecture
- Weapons systems
- Special operations and low intensity conflict
- Strategy
- Tactics
- Naval tactics

Public affairs and community service

- Criminal justice (also see Law above)
- Corrections
- Nonprofit administration
- Parks and recreation management
- Public administration
- Industrial and labor relations (also see Business above)
- Social work
- Gerontology

Animal

:For the Muppet Show character, see Animal (Muppet). For the professional wrestler, see Joseph Laurinaitis.

- Porifera (sponges)
- Ctenophora (comb jellies)
- Cnidaria (coral, jellyfish, anenomes)
- Placozoa (trichoplax)
- Subregnum Bilateria (bilateral symmetry)
- Acoelomorpha (basal)
- Orthonectida (flatworms, echinoderms, etc.)
- Rhombozoa (dicyemids)
- Myxozoa (slime animals)
- Superphylum Deuterostomia (blastopore becomes anus)
- Chordata (vertebrates, etc.)
- Hemichordata (acorn worms)
- Echinodermata (starfish, urchins)
- Chaetognatha (arrow worms)
- Superphylum Ecdysozoa (shed exoskeleton)
- Kinorhyncha (mud dragons)
- Loricifera
- Priapulida (priapulid worms)
- Nematoda (roundworms)
- Nematomorpha (horsehair worms)
- Onychophora (velvet worms)
- Tardigrada (water bears)
- Arthropoda (insects, etc.)
- Superphylum Platyzoa
- Platyhelminthes (flatworms)
- Gastrotricha (gastrotrichs)
- Rotifera (rotifers)
- Acanthocephala (acanthocephalans)
- Gnathostomulida (jaw worms)
- Micrognathozoa (limnognathia)
- Cycliophora (pandora)
- Superphylum Lophotrochozoa (trochophore larvae / lophophores)
- Sipuncula (peanut worms)
- Nemertea (ribbon worms)
- Phoronida (horseshoe worms)
- Ectoprocta (moss animals)
- Entoprocta (goblet worms)
- Brachiopoda (brachipods)
- Mollusca (mollusks)
- Annelida (segmented worms) Animals are a major group of organisms, classified as the kingdom Animalia or Metazoa. In general they are multicellular, capable of locomotion and responsive to their environment, and feed by consuming other organisms. Their body plan becomes fixed as they develop, usually early on in their development as embryos, although some undergo a process of metamorphosis later on. Along with sponges, gastropods, emus, dolphins and all other animals, Homo sapiens sapiens meet all the criteria above for membership in the group of organisms known as animals and they do not meet the criteria of the other groups. Some humans often consider themselves separate from animals, not on the grounds of biology, but through the use of "other contexts". Whilst self-delusion may be a unique characteristic of the human species it is not cause for exclusion from the Kingdom Animalia. The name animal comes from the Latin word animal, of which animalia is the plural, and ultimately from anima, meaning vital breath or soul.

Characteristics

Aristotle divided the living world between animals and plants, and this was followed by Carolus Linnaeus in the first hierarchical classification. Since then biologists have begun emphasizing evolutionary relationships, and so these groups have been restricted somewhat. For instance, microscopic protozoa were originally considered animals because they move, but are now treated separately. Kingdom Animalia has several characteristics that set it apart from other living things. First, animals are eukaryotic. This separates them from the Kingdom Monera. Second, animals are multicellular, which separates them from Kingdom Protista. Third, they are heterotrophic, setting them apart from Kingdom Plantae and several plant-like protists. Finally, Kingdom Animalia consists of organisms without cell walls, which makes it unique compared to Kingdom Plantae, algae, and Kingdom Fungi.

Structure

With a few exceptions, most notably the sponges (Phylum Porifera), animals have bodies differentiated into separate tissues. These include muscles, which are able to contract and control locomotion, and a nervous system, which sends and processes signals. There is also typically an internal digestive chamber, with one or two openings. Animals with this sort of organization are called metazoans, or eumetazoans when the former is used for animals in general. All animals have eukaryotic cells, surrounded by a characteristic extracellular matrix composed of collagen and elastic glycoproteins. This may be calcified to form structures like shells, bones, and spicules. During development it forms a relatively flexible framework upon which cells can move about and be reorganized, making complex structures possible. In contrast, other multicellular organisms like plants and fungi have cells held in place by cell walls, so develop by progressive growth. Also, unique to animal cells are the following intercellular junctions: tight junctions, gap junctions, and desmosomes.

Reproduction and development

Nearly all animals undergo some form of sexual reproduction. Adults are diploid or occasionally polyploid. They have a few specialized reproductive cells, which undergo meiosis to produce smaller motile spermatozoa or larger non-motile ova. These fuse to form zygotes, which develop into new individuals. Many animals are also capable of asexual reproduction. This may take place through parthenogenesis, where fertile eggs are produced without mating, or in some cases through fragmentation. A zygote initially develops into a hollow sphere, called a blastula, which undergoes rearrangement and differentiation. In sponges, blastula larvae swim to a new location and develop into a new sponge. In most other groups, the blastula undergoes more complicated rearrangement. It first invaginates to form a gastrula with a digestive chamber, and two separate germ layers - an external ectoderm and an internal endoderm. In most cases, a mesoderm also develops between them. These germ layers then differentiate to form tissues and organs. Animals grow by indirectly using the energy of sunlight. Plants use this energy to turn air into simple sugars using a process known as photosynthesis. These sugars are then used as the building blocks which allow the plant to grow. When animals eat these plants (or eat other animals which have eaten plants), the sugars produced by the plant are used by the animal. They are either used directly to help the animal grow, or broken down, releasing stored solar energy, and giving the animal the energy required for motion. This process is known as glycolysis.

Origin and fossil record

Animals are generally considered to have evolved from flagellate protozoa. Their closest living relatives are the choanoflagellates, collared flagellates that have the same structure as certain sponge cells do. Molecular studies place them in a supergroup called the opisthokonts, which also include the fungi and a few small parasitic protists. The name comes from the posterior location of the flagellum in motile cells, such as most animal sperm, whereas other eukaryotes tend to have anterior flagella. The first fossils that might represent animals appear towards the end of the Precambrian, around 600 million years ago, and are known as the Vendian biota. These are difficult to relate to later fossils, however. Some may represent precursors of modern phyla, but they may be separate groups, and it is possible they are not really animals at all. Aside from them, most animal phyla with known phyla make a more or less simultaneous appearance during the Cambrian period, about 570 million years ago. It is still disputed whether this event, called the Cambrian explosion, represents a rapid divergence between different groups or a change in conditions that made fossilization possible.

Groups of animals

The sponges (Porifera) diverged from other animals early. As mentioned, they lack the complex organization found in most other phyla. Their cells are differentiated, but not organized into distinct tissues. Sponges are sessile and typically feed by drawing in water through pores all over the body, which is supported by a skeleton typically divided into spicules. The extinct Archaeocyatha, which have fused skeletons, may represent sponges or a separate phylum. Among the eumetazoan phyla, two are radially symmetric and have digestive chambers with a single opening, which serves as both the mouth and the anus. These are the Cnidaria, which include anemones, corals, and jellyfish, and the Ctenophora or comb jellies. Both have distinct tissues, but they are not organized into organs. There are only two main germ layers, the ectoderm and endoderm, with only scattered cells between them. As such, these animals are sometimes called diploblastic. The tiny phylum Placozoa is similar, but individuals do not have a permanent digestive chamber. The remaining animals form a monophyletic group called the Bilateria. For the most part, they are bilaterally symmetric, and often have a specialized head with feeding and sensory organs. The body is triploblastic, i.e. all three germ layers are well-developed, and tissues form distinct organs. The digestive chamber has two openings, a mouth and an anus, and there is also an internal body cavity called a coelom or pseudocoelom. There are exceptions to each of these characteristics, however - for instance adult echinoderms are radially symmetric, and certain parasitic worms have extremely simplified body structures. Genetic studies have considerably changed our understanding of the relationships within the Bilateria. Most appear to belong to four major lineages: # Deuterostomes # Ecdysozoa # Platyzoa # Lophotrochozoa In addition to these, there are a few small groups of bilaterians with relatively similar structure that appear to have diverged before these major groups. These include the Acoelomorpha, Rhombozoa, and Orthonectida. The Myxozoa, single-celled parasites that were originally considered Protozoa, are now believed to have developed from the Bilateria as well.

Deuterostomes

Deuterostomes differ from the other Bilateria, called protostomes, in several ways. In both cases there is a complete digestive tract. However, in protostomes the initial opening (the archenteron) develops into the mouth, and an anus forms separately. In deuterostomes this is reversed. In most protostomes cells simply fill in the interior of the gastrula to form the mesoderm, called schizocoelous development, but in deuterostomes it forms through evagination of the endoderm, called enterocoelic pouching. Deuterostomes also have a dorsal, rather than a ventral, nerve chord and their embryos undergo different cleavage. All this suggests the deuterostomes and protostomes are separate, monophyletic lineages. The main phyla of deuterostomes are the Echinodermata and Chordata. The former are radially symmetric and exclusively marine, such as sea stars, sea urchins, and sea cucumbers. The latter are dominated by the vertebrates, animals with backbones. These include fish, amphibians, reptiles, birds, and mammals. In addition to these, the deuterostomes also include the Hemichordata or acorn worms. Although they are not especially prominent today, the important fossil graptolites may belong to this group. The Chaetognatha or arrow worms may also be deuterostomes, but this is less certain.

Ecdysozoa

The Ecdysozoa are protostomes, named after the common trait of growth by moulting or ecdysis. The largest animal phylum belongs here, the Arthropoda, including insects, spiders, crabs, and their kin. All these organisms have a body divided into repeating segments, typically with paired appendages. Two smaller phyla, the Onychophora and Tardigrada, are close relatives of the arthropods and share these traits. The ecdysozoans also include the Nematoda or roundworms, the second largest animal phylum. Roundworms are typically microscopic, and occur in nearly every environment where there is water. A number are important parasites. Smaller phyla related to them are the Nematomorpha or horsehair worms, which are visible to the unaided eye, and the Kinorhyncha, Priapulida, and Loricifera, which are all microscopic. These groups have a reduced coelom, called a pseudocoelom. The remaining two groups of protostomes are sometimes grouped together as the Spiralia, since in both embryos develop with spiral cleavage.

Platyzoa

The Platyzoa include the phylum Platyhelminthes, the flatworms. These were originally considered some of the most primitive Bilateria, but it now appears they developed from more complex ancestors. A number of parasites are included in this group, such as the flukes and tapeworms. Flatworms lack a coelom, as do their closest relatives, the microscopic Gastrotricha. The other platyzoan phyla are microscopic and pseudocoelomate. The most prominent are the Rotifera or rotifers, which are common in aqueous environments. They also include the Acanthocephala or spiny-headed worms, the Gnathostomulida, Micrognathozoa, and possibly the Cycliophora. These groups share the presence of complex jaws, from which they are called the Gnathifera.

Lophotrochozoa

The Lophotrochozoa include two of the most successful animal phyla, the Mollusca and Annelida. The former includes animals such as snails, clams, and squids, and the latter comprises the segmented worms, such as earthworms and leeches. These two groups have long been considered close relatives because of the common presence of trochophore larvae, but the annelids were considered closer to the arthropods, because they are both segmented. Now this is generally considered convergent evolution, owing to many morphological and genetic differences between the two phyla. The Lophotrochozoa also include the Nemertea or ribbon worms, the Sipuncula, and several phyla that have a fan of cilia around the mouth, called a lophophore. These were traditionally grouped together as the lophophorates, but it now appears they are paraphyletic, some closer to the Nemertea and some to the Mollusca and Annelida. They include the Brachiopoda or lamp shells, which are prominent in the fossil record, the Entoprocta, the Phoronida, and possibly the Ectoprocta or moss animals.

History of classification

In Linnaeus' original scheme, the animals were one of three kingdoms, divided into the classes of Vermes, Insecta, Pisces, Amphibia, Aves, and Mammalia. Since then the last four have all been subsumed into a single phylum, the Chordata, whereas the various other forms have been separated out. The above lists represent our current understanding of the group, though there is some variation from source to source.

Usage of the word animal

In everyday usage animal refers to any member of the animal kingdom that is not a human being, and sometimes excludes insects (although including such arthropods as crabs). This confusion stems primarily from the familiarity with zoo animals, farm animals and pets, not from an analytical distinction between insects, humans and the rest of the animal kingdom.

Examples

Some well-known types of animals, listed by their common names:
- alpaca, ant, antelope, badger, bat, bear, bee, beetle, bird, bison, butterfly, cat, chicken, cockroach, coral, cow, deer, dinosaur, dog, dolphin, earthworm, elephant, elk, fish, fly, fox, frog, giraffe, goat, gorilla, hippopotamus, horse, human, iguana, jellyfish, kangaroo, lion, lizard, llama, lynx, monkey, mouse, nightingale, octopus, owl, ox, parrot, penguin, pig, quail, rabbit, rat, rhinoceros, salamander, scorpion, seahorse, shark, sheep, sloth, snake, spider, squid, starfish, tiger, turtle, urial, vole, whale, wolf, yak, zebra

References

External links

- [http://www.animool.com/animals/index.jsp Animals Search Engine]
- [http://www.wikianimals.com wikianimals.com] - Documenting the animal kingdom
- [http://tolweb.org/tree?group=Animals&contgroup=Eukaryotes Tree of Life]
- [http://www.arkive.org A Multimedia Database of Various UK or Endangered Species]
- [http://freepages.genealogy.rootsweb.com/~wakefield/animals.html Animals and Birds Names] - Large table of words: animal, collective, male, female, young, & home
- [http://www273.pair.com/med/words/animal_adjectives.htm English Animal Adjectives]
- [http://www.georgetown.edu/faculty/ballc/animals/animals.html Sounds of the World's Animals] - animal sounds in many languages
- [http://www.findsounds.com/ FindSounds - Search the Web for Sounds] - sound files including animal sound files
- [http://www.australianfauna.com/ Australian Animals]
- [http://www.animalreviews.com AnimalReviews] - animals reviewed and evaluated
- [http://animals.timduru.org/ The animal photo archive] - Photos of animals
- [http://www.wildlife-photo.org Photo gallery of animals pictures from the entire world.]
- [http://www.wildlife-photo.org/birds_list.htm Birds Name Check List in Latin, English, Russian and Hebrew.]
- [http://www.wildanimalsonline.com Wild Animals Online] - an online encyclopedia of wild animals - facts, photos Category:Animals zh-min-nan:Tōng-bu̍t ko:동물 ms:Haiwan ja:動物 simple:Animal th:สัตว์

History of zoology (since Darwin)

This article is part of the
Zoology series.

History of zoology (before Darwin)

History of zoology (since Darwin)

Charles Darwin gave new stimulus and new direction to morphology and physiology, by uniting them as part of a common biological theory: the theory of organic evolution but a part of the wider doctrine of universal evolution based on the laws of physics and chemistry. The immediate result was, a reconstruction of the classification of animals upon a genealogical basis, and an investigation of the individual development of animals, and early attempts to determine their genetic relationships. Warning: this is largely based on the 1911 Encyclopedia Brittannica, and contains several errors.

Early 20th century work

The studies which occupied Darwin himself subsequent to the publication of the Origin of Species, that is the explanations of animal and plant mechanisms, coloring, habits, which confer advantages to the individuals within a species, were only gradually being carried further in the early 20th century. Much important work in this direction was done by Fritz Muller (Für Darwin), by Herman Muller (Fertilization of Plants by Insects), by August Weismann (memoirs translated by Meldola) by Edward B. Poulton (see his addresses and memoirs published in the Transactions of the Entomological Society and elsewhere), and by Abbot Thayer (Concealing Coloration in the Animal Kingdom, Macmillan & Co., 1910). In the field of what would become known as genetics, the laws of variation and heredity (originally known as thremmatology), there was considerable progress during this period. The progress of microscopy during this era began to give a clearer understanding of the structural facts connected with the origin of the egg-cell and sperm-cell and the process of fertilization.

Mendel and zoology

Gregor Mendel's experiments hybridizing certain cultivated varieties of plants were published in 1865, but failed to attract notice until thirty-five years later in the early 20th century, sixteen years after his death (see Mendelism). Mendel's object was to gain a better understanding of the principles of heredity. Mendel made his chief experiments with cultivated varieties of the self-fertilizing edible pea. He selected a variety with one marked structural feature and crossed it with another variety in which that feature was absent. Instances of his selected varieties are the tall variety which he hybridized with a dwarf variety, a yellow-seeded variety which he hybridized with a green-seeded variety, and again a smooth-seeded variety which he hybridized with a wrinkle-seeded variety. In each set of experiments he concentrated his attention on the one character selected for observation. Having obtained a first hybrid generation, he allowed the hybrids to self-fertilize, and recorded the result in a large number of instances (a thousand or more) as to the number of individuals in the first, second, third, and fourth generations in which the character selected for experiment made its appearance. In the first hybrid generation formed by the union of the reproductive germs of the positive variety (that possessing the structural character selected for observation) with those of the negative variety, it is not surprising that all or nearly all the individuals were found to exhibit, as a result of the mixture, the positive character. In subsequent generations produced by self-fertilization of the hybrids it was found that the positive character was not present in all the individuals, but that a result was obtained showing that in the formation of the reproductive cells (ova and sperms) of the hybrid, half were endowed with the positive character and half with the negative. Consequently the result of the haphazard pairing of a large number of these two groups of reproductive cells was to yield, according to the regular law of chance combination, the proportion 1 PP, 2 PN, 1 NN, where P stands for the positive character and N for its absence or negative character - the positive character being accordingly present in three-fourths of the offspring and absent from one-fourth. The fact that in the formation of the reproductive cells of the hybrid generation the material which carries the positive quality is not subdivided so as to give a half-quantity to each reproductive cell, but on the contrary is apparently distributed as an undivided whole to half only of the reproductive cells and not at all to the remainder, is the important inference from Mendel's experiments. Whether this inference is applicable to other classes of cases than those studied by Mendel and his followers is a question which is still under investigation. The failure of the material carrying a positive character to divide so as to distribute itself among all the reproductive cells of a hybrid individual, and the limitation of its distribution to half only of those cells, must prevent the swamping of a newly appearing character in the course of the inter-breeding of those individuals possessed of the character with those which do not possess it. The tendency of the proportions in the offspring of 1 PP, 2 PN, 1 NN is to give in a series of generations a regular reversion from the hybrid form PN to the two pure races, viz, the race with the positive character simply and the race with the total absence of it. It has been maintained that this tendency to a severance of the hybrid stock into its components must favour the persistence of a new character of large volume suddenly appearing in a stock, and the observations of Mendel have been held to favour in this way the views of those who hold that the variations upon which natural selection has acted in the production of new species are not small variations but large and discontinuous. It does not, however, appear that large variations would thus be favoured any more than small ones, nor that the eliminating action of natural selection upon an unfavourable variation could be checked. A good deal of confusion has arisen in the discussions of this latter topic, owing to defective nomenclature. By some writers the word mutation is applied only to large and suddenly appearing variations which are found to he capable of hereditary transmission, whilst the term fluctuation is applied to small variations whether capable of transmission or not. By others the word fluctuation is apparently applied only to those small acquired variations due to the direct action of changes in food, moisture and other features of the environment. It is no discovery that this latter kind of variation is not hereditable, and it is not the fact that the small variations, to which Darwin attached great but not exclusive importance as the material upon which natural selection operates, are of this latter kind. The most instructive classification of the variations exhibited by fully formed organisms consists in the separation in the first place of those which arise from antecedent congenital, innate, constitutional, or germinal variations from those which arise merely from the operation of variation of the environment or the food-supply upon normally constituted individuals. The former are innate variations, the latter are superimposed variations (so-called acquired variations). Both innate and superimposed variations are capable of division into those which are more and those which are less obvious to the human eye. Scarcely perceptible variations of the innate class are regularly and invariably present in every new generation of every species of living thing. Their greatness or smallness so far as human perception goes is not of much significance; their real importance in regard to the origin of new species depends on whether they are of value to the organism and therefore capable of selection in the struggle for existence. An absolutely imperceptible physiological difference arising as a variation may be of selective value, and it may carry with it correlated variations which appeal to the human eye but are of no selective value themselves. The present writer has, for many years, urged the importance of this consideration. The views of Hugo de Vries and others as to the importance of saltatory variation, the soundness of which was still by no means generally accepted in 1910, may be gathered from the articles Mendelism and variation. A due appreciation of the far-reaching results of correlated variation must, it appears, give a new and distinct explanation to the phenomena which are referred to as large mutations, discontinuous variation, and saltatory evolution. Whatever value is to be attached to Mendel's observation of the breaking up of self-fertilized hybrids of cultivated varieties into the two original parent forms according to the formula 1 PP, 2 PN, 1 NN, it cannot be considered as more than a contribution to the extensive investigation of heredity which still remains to be carried out. The analysis of the specific variations of organic form so as to determine what is really the nature and limitation of a single character or individual variation, and whether two such true and strictly-defined single variations of a single structural unit can actually blend when one is transmitted by the male parent and the other by the female parent, are matters which have yet to be determined. We do not yet know whether such absolute blending is possible or not, or whether all apparent blending is only a more or less minutely subdivided mosaic of non-combinable characters of the parents, in fact whether the combinations due to heredity in reproduction are ever analogous to chemical compounds or are always comparable to particulate mixtures. The attempt to connect Mendel's observation with the structure of the sperm-cells and egg-cells of plants and animals has already been made. The suggestion is obvious that the halving of the number of nuclear threads in the reproductive cells as compared with the number of those present in the ordinary cells of the tissues, as a phenomenon which has now been demonstrated as universal, may he directly connected with the facts of segregation of hybrid characters observed by Mendel. The suggestion requires further experimental testing, for which the case of the parthenogenetic production of a portion of the offspring, in such insects as the bee, offers a valuable opportunity for research. Another important development of Darwin's conclusions deserves special notice here, as it is the most distinct advance in the department of bionomics since Darwin's own writings, and at the same time touches questions of fundamental interest. The matter strictly relates to the consideration of the causes of variation, and is as follows. The fact of variation is a familiar one. No two animals, even of the same brood, are alike: whilst exhibiting a close similarity to their parents, they yet present differences, sometimes very marked differences, from their parents and from one another. Jean-Baptiste Lamarck had put forward the hypothesis that structural alterations acquired by (that is to say, superimposed upon) a parent in the course of its life are transmitted to the offspring, and that, as these structural alterations are acquired by an animal or plant in consequence of the direct action of the environment, the offspring inheriting them would as a consequence not unfrequently start with a greater fitness for those conditions than its parents started with. In its turn, being operated upon by the conditions of life, it would acquire a greater development of the same modification, which it would in turn transmit to its offspring. In the course of several generations, Lamarck argued, a structural alteration amounting to such difference as we call specific might be thus acquired. The familiar illustration of Lamarck's hypothesis is that of the giraffe, whose long neck might, he suggested, has been acquired by the efforts of a primitively short-necked race of herbivores who stretched their necks to reach the foliage of trees in a land where grass was deficient, the effort producing a distinct elongation in the neck of each generation, which was then transmitted to the next. This process is known as direct adaptation; there is no doubt that such structural adaptations are acquired by an animal in the course of its life, though such changes are strictly limited in degree and rare rather than frequent and obvious. Whether such acquired characters can be transmitted to the next generation is a separate question. It was not proved by Lamarck that they can be and, indeed, never has been proved by actual observation. Nevertheless it has been assumed, and also indirectly argued, that such acquired characters must be transmitted. Darwin's great merit was that he excluded from his theory of development any necessary assumption of the transmission of acquired characters. He pointed to the admitted fact of congenital variation, and he showed that congenital variations are arbitrary and, so to speak, non-significant.

Congenital variation

Their causes are extremely difficult to trace in detail, but it appears that they are largely due to a shaking up of the living matter which constitutes the fertilized germ or embryo-cell, by the process of mixture in it of the substance of two cells - the germ cell and the sperm-cell - derived from two different individuals. Other mechanical disturbances may assist in this production of congenital variation. Whatever its causes, Darwin showed that it is all-important. In some cases a pair of animals produce ten million offspring, and in such a number a lar