theory of acquired characteristics:the concept, popularized by Lamarck, that traits gained during a lifetime can then be passed on to the next generation by genetic means; considered invalid today.
theory: a step in the scientific method in which a statement is generated on the basis of highly confirmed hypotheses and is used to generalize about conditions not yet tested.
therian mammals: members of the subclass Theria; the "live-bearing" mammals, including the marsupials and placental mammals.
thermal prospection: a remote sensing method used in aerial reconnaissance. It is based on weak variations in temperature which can be found above buried structures whose thermal properties are different from those of their surroundings.
thermography: a non-photographic technique which uses thermal or heat sensors in aircraft to record the temperature of the soil surface. Variations in soil temperature can be the result of the presence of buried structures.
thermoluminescence dating (TL): a chronometric dating method based on the fact that some materials, when heated, give off a flash of light. The intensity of the light is proportional to the amount of radiation the sample has been exposed to and the length of time since the sample was heated. It has much in common with electron spin resonance (ESR).
Thiessen polygons: a formal method of describing settlement patterns based on territorial divisions centered on a single site; the polygons are created by drawing straight lines between pairs of neighboring sites, then at the mid-point along each of these lines, a second series of lines are drawn at right angles to the first. Linking the second series of lines creates the Thiessen polygons.
thin-section analysis: a technique whereby microscopic thin sections are cut from a stone object or potsherd and examined with a petrological microscope to determine the source of the material.
threat gesture: a physical activity used by one animal to threaten another animal. Some threat gestures are staring, shaking a branch, and lunging toward another animal.
Three Age System: a classification system devised by C.J. Thomsen for the sequence of technological periods (stone, bronze, and iron) in Old World prehistory. It established the principle that by classifying artifacts, one could produce a chronological ordering.
thymine: a pyrimidine found in RNA.
till: sediments laid down directly by glacial ice. Commonly consists of unsorted angular rock fragments mixed with clay.
tipi: a relatively large conical skin and pole tent used in the Plains area.
toilet claw: a claw found on the second toe of prosimians that functions in grooming.
tool: an object that appears to have been created for a specific purpose.
topographic map: a map which accurately depicts the physical features and relief of an area.
topography: the physical ground features of an area.
totem: a plant or animal whose name is adopted by a clan and that holds a special significance for its members, usually related to their mythical ancestry.
township: a square area, containing 36 sections; a major unit of the legal subdivision system.
trace element analysis: the use of chemical techniques, such as neutron activation analysis, or X-ray fluorescence spectrometry, for determining the incidence of trace elements in rocks. These methods are widely used in the identification of raw material sources for the production of stone tools.
tradition: a continuum of gradational culture change through time representing the unbroken development of a single culture.
trait: any discrete cultural element; or, one aspect of the phenotype.
trajectory: in systems thinking, this refers to the series of successive states through which the system proceeds over time. It may be said to represent the long-term behavior of the system.
transect: a linear sampling area.
transfer RNA (tRNA):within the ribosome, a form of RNA that transports amino acids into the positions coded in the mRNA.
transformation: a radiation change in morphology among homologous structures.
transformational grammar: Noam Chomsky's theory of linguistics, based on the fact that a single meaning may be expressed in different forms.
transformational rules: according to transformational grammar, the techniques by which deep structure is translated into surface structure.
transhumance: seasonal movement of livestock between upland and lowland pastures.
transit: a sophisticated optical surveying instrument similar to an alidade, except that it is mounted directly on a tripod, rather than resting on a plane
translocation: a form of chromosomal aberration in which segments of chromosomes become detached and reunite to other nonhomologous chromosomes.
travelers: hunter-gatherers who follow a regular yearly round, occupying a series of campsites for brief periods when a valued resource is available in the vicinity of each site (a logistical pattern).
tree-ring dating: a chronometric dating method in which the age of a wood sample is determined by counting the number of annual growth rings.
trend surface analysis: the aim of trend surface analysis is to highlight the main features of a geographic distribution by smoothing over some of the local irregularities. In this way, important trends can be isolated from the background "noise" more clearly.
tribe: a descent and kinship-based group in which subgroups are clearly linked to one another, with the potential of uniting a large number of local groups for common defense or warfare. Unlike bands, tribes are usually settled farmers, though they also include nomadic pastoral groups whose economy is based on exploitation of livestock. Individual communities tend to be integrated into the larger society through kinship ties.
true brachiation: a form of locomotion found in the lesser apes in which the body, suspended from above, is propelled by arm swinging as the animal rapidly moves hand-over-hand along a branch.
true breeding: showing the same traits without exception over many generations.
tuff: geological formation composed of compressed volcanic ash.
tundra: a type of landscape where the ground is frozen solid throughout most of the year but thaws slightly during the summer.
Tupaiidae: family of the order Insectivora that includes the tree shrews.
Turner's syndrome: a genetic disease characterized by forty-five chromosomes with a sex chromosome count of X-; phenotypically female, but sterile.
tuyere: a ceramic blowtube used in the process of smelting.
twin studies: comparisons of monozygotic twins to dizygotic twins for the purpose of estimating the degree of environmental versus genetic influence operating on a specific trait.
tympanic membrane: the eardrum.
type: a distinctive formal artifact class defined by the consistent clustering of attributes and restricted in space and time, e.g. the "Folsom Point" is a projectile point "type".
typology: the systematic organization of artifacts into types on the basis of shared attributes.
ultrasound: a method of taking a picture of the fetus using sound waves.
unconformity: the surface of a stratum that represents a break in the stratigraphic sequence.
underwater reconnaissance: geophysical methods of underwater survey include (1) a proton magnetometer towed behind a survey vessel, so as to detect iron and steel objects which distort the earth's magnetic field; (2) sidescan sonar that transmits sound waves in a fan-shaped beam to produce a graphic image of surface features on the sea-bed; (3) a sub-bottom profiler that emits sound pulses which bounce back from features and objects buried beneath the sea floor.
uniface: a stone artifact flaked only on one surface.
unifacial flaking: the removal of secondary flakes from only one surface of a stone nucleus.
uniformitarianism: the principle which states that physical forces working today to alter the earth were also in force and working in the same way in former times.
unilineal descent group: a kin group in which membership is inherited only through either the paternal or the maternal line, as the society dictates.
unilineal evolution: a pattern of cultural progress through a sequence of evolutionary stages; the basic premise of the early cultural evolutionists.
unstructured interview: an ethnographic data-gathering technique usually used in the early stages of one's fieldwork in which interviewees are asked to respond to broad, open-ended questions.
uracil: a pyrimidine found in RNA.
uranium series dating: a dating method based on the radioactive decay of isotopes of uranium. It has proved particularly useful for the period before 50,000 years ago, which lies outside the time range of radiocarbon dating.
urbanization: the proportionate rise in the number of people living in cities in comparison to the number living in rural areas.
urbanized society: a society in which a majority of people live in cities.
use-wear: polish, striations, breakage, or minor flaking which develop on a tool's edge during use. Microscopic examination and study of the wear may indicate the past function of tools.
utilized flake: a stone flake used for a tool without deliberate retouch, but exhibiting use-wear.
utilized material: pieces of stone that have been used without modification.
variable: any property that may be displayed in different forms.
varnas caste: groups in Hindu India associated with certain occupations.
varves: fine layers of alluvium sediment deposited in glacial lakes. Their annual deposition makes them a useful source of dating.
vasoconstriction: the constriction of the capillaries in the skin in response to cold temperatures.
vasodilation: the opening up of the capillaries of the skin in response to warm temperatures, thus increasing the flow of blood to the surface of the
ventral: the front or bottom side of an animal or artifact.
Venus figurines: small Upper Paleolithic statues characterized by exaggerated breasts and buttocks and very stylized heads, hands, and feet.
vertebrate: a member of the subphylum Vertebrate; possesses a bony spine or vertebral column.
vertical angle:in mapping, the angle of sight measured on the vertical plane.
vertical circle: with major surveying instruments, the graduated vertical table around which the sighting telescope rotates; used to measure the vertical angle.
vertical clinging and leaping: a method of locomotion in which the animal clings vertically to a branch and moves between branches by leaping vertically from one to another. The animal moves on the ground by hopping or moves bipedally.
vertical datum: a base measurement point from which all elevations are determined.
vertical distance: the measurement of distance (or elevations) on a true vertical plane.
vertical provenience: the vertical position of objects within a site determined in relation to a vertical datum or datum plane, as well as to the local ground surface.
Victoriapithecidae: family of Early and Middle Miocene Old World monkeys from north and east Africa.
volcanic ash: layers of airborne pumice resulting from violent volcanic eruptions. Provide valuable dating markers when found in sites.
water table: the level of water under the earth.
wealth: the accumulation of material objects that have value within a society.
weathering zone: in pedology, the depth to which soil processes are operational.
weathering: the natural chemical or physical alteration of an object or deposit through time.
weir: an aboriginal fish-trap based on a fence or barrier of stakes or rocks built across a stream.
welded tuff: a rock formed of consolidated pumice or volcanic ash. Occasionally used as a raw material for lithic artifacts.
Wheeler box-grid: an excavation technique developed by Mortimer Wheeler from the work of Pitt-Rivers, involving the retaining of intact baulks of earth between excavation grid squares, so that different layers can be correlated across the site in the vertical profiles.
white blood cell: see leukocyte.
Wisconsin(an) glaciation: the latest major episode of glacial advance in the Pleistocene of North America; from about 70,000 to 10,000 B.P.
workday: the culturally established number of hours that a person ideally spends at work each day.
world system: a term coined by the historian Wallerstein to designate an economic unit, articulated by trade networks extending far beyond the boundaries of individual political units (nation states), and linking them together in a larger functioning unit.
X chromosome: the larger of the two sex chromosomes. Normal females possess two X chromosomes; normal males possess one X and one Y chromosome.
X-linked: a term that refers to genes on the X chromosome.
X-ray diffraction analysis: a technique used in identifying minerals present in artifact raw materials; it can also be used in geomorphological contexts to identify particular clay minerals in sediments, and thus the specific source from which the sediment was derived.
X-ray fluorescence spectrometry (XRF): a method used in the analysis of artifact composition, in which the sample is irradiated with a beam of X-rays which excite electrons associated with atoms on the surface.
XTENT modeling: a method of generating settlement hierarchy, that overcomes the limitations of both central place theory and Thiessen polygons; it assigns territories to centers based on their scale, assuming that the size of each center is directly proportional to its area of influence. Hypothetical political maps may thus be constructed from survey data.
Y chromosome: the smaller of the two sex chromosomes. Normal females possess no Y chromosome; normal males possess one X and one Y chromosome.
Y-linked: a term that refers to genes on the Y chromosome.
yolk sac: a sack formed from embryonic tissue in the amniote egg that contains yolk.
zooarchaeology: the study of faunal remains found in archaeological sites and their cultural significance.
zoomorphic: "animal-like". refers to art-work or decorated objects with an animal motif or appearance.
zygomatic arch: the "cheek" bone; an arch of bone on the side of the skull.
zygote: a fertilized ovum.
zygotic mortality: a form of reproductive isolation in which fertilization occurs but development stops soon after preventing much of the warm blood from reaching the surface of the body, where heat could be lost.