tribe Any of a variety of social units, including some defined by unilineal descent and some defined by ethnic origin. Cultural anthropologists now usually apply the term to a unit of social organization that is culturally homogeneous and consists of multiple kinship groups—such as the family, lineage, or can —that prohibit marriages within themselves but endorse or require marriages with persons of the other kinship groups. (See exogamy and endogamy.) Most tribes are organized as unitary political entities, within which people share a common language and culture. Some tribes are spread across large territories, and individual members may never meet or know all of the others. Some are small groups, confined to a limited terri¬ tory, sometimes a single small island, within which everyone knows every¬ one else very well. What unites societies of such diverse scales as being “tribal” is their own internal sense of “being a single people,” but— anthropologists would add—a people that lacks the equipment of citizen¬ ship, a constitution, or a formalized legal system that would define them as a nation-state. Throughout most of the history of modem cultural anthro¬ pology, the terms tribe and primitive were usually linked; however, in recent years primitive has been avoided by most anthropologists because it appears to carry with it an unintended judgment of the moral or techno¬ logical development of a people. See also ethnic group.
tribe (Greek, phylai; Roman, tribus ) In ancient Greece and Rome, any of a group of political and demographic subdivisions of the population. In Greece the groups divided into tribes were distinct by location, dialect, and tradition, and they included the Ionians, Dorians, Achaeans, and Aeto- lians. In Attica, Cleisthenes replaced the 4 Ionian tribes with 10 new tribes, each of which was named after a local hero; these came to develop politi¬
cal and civic functions, including the election of magistrates. The demes developed out of the tribal system. In Rome the tribes formed the 3 (later 4, and still later 35) original divisions of Roman citizens. These were the basis of military levies, property tax, census taking, and voting units in political assemblies.
tribology \tri-'ba-lo-je\ Study of the interactions of sliding surfaces. It includes three subjects: friction, wear, and lubrication. Many manifesta¬ tions of tribology are beneficial and make modem life possible. Many others are serious nuisances, and careful design is necessary to overcome problems caused by excessive friction or wear. Friction uses up, or wastes, a substantial amount of the energy generated by humans; in addition, a great deal of productive capacity is devoted to replacing objects that have worn out.
tribune In ancient Rome, any of various military and civil officials. Military tribunes were originally infantry commanders. In the early repub¬ lic there were six to a legion; some were appointed by consuls or mili¬ tary commanders, others elected by the people. During the Roman empire (from 27 bc), the emperor nominated military tribunes, the office of which was considered preliminary to a senatorial or equestrian career (see eques ). Of the civil tribunes, the most important were the tribunes of the plebs (see plebeian), who were elected in the plebeian assembly. By 450 bc there were 10 plebeian tribunes, who were elected annually with the right to intervene in cases of unjust acts of consuls or magistrates by saying “Veto” (meaning “I forbid it”). The office became powerful; its powers were cur¬ tailed by Sul A but restored by Pompey. Under the empire the powers of the plebeian tribunes passed to the emperor.
tricarboxylic \ I trI- I kar-bak-'sil-ik\ acid cycle or Krebs cycle or citric-acia cycle Last stage of the chemical processes by which living cells obtain energy from foodstuffs. Described by Hans Adolf Krebs in 1937, the reactions of the cycle have been shown in animals, plants, microorganisms, and fungi, and it is thus a feature of cell chemistry shared by all types of life. It is a complex series of reactions beginning and end¬ ing with the compound oxaloacetate. In addition to re-forming oxaloac- etate, the cycle produces carbon dioxide and the energy-rich compound ATP. The enzymes that catalyze each step are located in mitochondria in animals, in chloropasts in plants, and in the cell membrane in microor¬ ganisms. The hydrogen atoms and electrons that are removed from inter¬ mediate compounds formed during the cycle are channeled ultimately to oxygen in animal cells or to carbon dioxide in plant cells.
Triceratops \tn-'ser-3-,taps\ genus of large, plant-eating ornithischian dinosaurs of the Late Cretaceous Epoch (99-65 million years ago). Tricer¬ atops had a very long skull (some more than 6 ft [1.8 mj long); a large bony frill about the neck; a relatively short, pointed horn on the nose; a beaklike mouth; and two pointed horns, more than 3.3 ft (1 m) long, above the eyes. Adults weighed 4-5 tons (3.6^4.5 metric tons) and grew up to 30 ft (9 m) long. The limbs were very stout, and the hind limbs were more massive than the forelimbs.
trichina Uri-'kI-noX Species ( Trichinella spiralis) of parasitic nematode, found worldwide, that causes the dis¬ ease trichinosis. Trichinae (or trichi¬ nas), 0.06-0.2 in. (1.5-4 mm) long, mate in the host’s small intestine.
Fertilized females penetrate the intestinal wall and release larvae, which the blood carries throughout the body. The larvae grow, mature, and become encysted within muscle tissue. The digestive juices of an ani¬ mal that eats the muscle tissue break down the cyst, liberating the larvae for further development; the worms mature, and the cycle begins again.
trichinosis \ 1 tri-ko- , no-s3s\ Disorder caused by the roundworm trichina, commonly acquired from undercooked infested pork. Larval worms invade the small intestine, maturing within a week. Fertilized females deposit new larvae, which are carried by the blood, notably to the muscles (most often the diaphragm, eyes, throat, and tongue), where they encap¬ sulate and may remain alive for years. Though trichinosis usually even¬ tually subsides, it may be fatal if the heart and brain are involved. Few infected persons have sufficient parasites to produce symptoms (includ¬ ing diarrhea, nausea, and fever, followed by pain, stiffness, and swelling
Trichina encysted in muscle
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trichomonad > Trimble I 1937
of various muscular structures). Anti-inflammatory drugs can relieve symptoms; thiabendazole may effectively destroy parasites in the intes¬ tine. There is no practical way to detect trichinous pork; the surest safe¬ guard remains thorough cooking.
trichomonad \ I tri-k3-'mo- l nad\ Any protozoan of the zooflagellate order Trichomonadida. Trichomonads have three to six flagella, and they may have one or multiple nuclei. Most inhabit the digestive systems of animals. Three species occur in humans: T. hominis in the intestine, T. vaginalis in the vagina, and T. buccalis in the mouth.
trickster tale In oral traditions worldwide, a story of deceit, magic, and violence perpetrated by a mythical animal-human (trickster). The trickster-hero is both creator god and innocent fool, evil destroyer and childlike prankster. Coyote, the trickster of tales from American Indian peoples in California and the Southwest, is one of the most widely known. In the Pacific Northwest, the trickster is Raven. Many African peoples also have tales about tricksters (hare, spider, tortoise, etc.), which slaves brought to the New World. Tales involving the trickster Brer Rabbit were given literary form by Joel Chandler Harris.
Trident missile U.S.-made SUBMARINE-Iaunched ballistic missile. The most advanced Trident missiles, deployed by the U.S. Navy since 1990 and by the Royal Navy since 1994, are more accurate than most land- based ballistic missiles. Their extended range (up to 7,000 mi [11,300 km]) allows the submarines that carry them to patrol almost anywhere, making detection extremely difficult. Each missile is capable of carrying more than 10 multiple independently targeted reentry vehicles (see MIRV), though arms-control considerations limit the actual number to as few as three.