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acclimation  Short-term physiologic responses to a stress, usually occurring within minutes or hours.
acclimatization  Long-term physiologic responses to a stress, usually taking from days to months.
Acheulian tradition  A stone tool technology that appears first with Homo erectus and is characterized by the development of hand axes and other bifacial tools.
adaptation  The process of successful interaction between a population and an environment. Cultural or biological traits that offer an advantage in a given environment are adaptations.
adaptive radiation  The formation of many new species following the availability of new environments or the development of a new adaptation.
African replacement model  The hypothesis that modern humans evolved as a new species in Africa between 150,000 and 200,000 years ago and then spread throughout the Old World, replacing preexisting archaic human populations.
age at menarche  The age at which a human female experiences her first menstrual period.
age-sex structure  The number of males and females in different age groups of a population.
allele  The alternative form of a gene or DNA sequence that occurs at a given locus. Some loci have only one allele, some have two, and some have many alternative forms. Alleles occur in pairs, one on each chromosome.
Allen’s rule  States that mammals in cold climates tend to have shorter and bulkier limbs, allowing less loss of body heat, whereas mammals in hot climates tend to have long, slender limbs, allowing greater loss of body heat.
allometry  The study of the change in proportion of various body parts as a consequence of their growth at different rates.
Alu insertions  A sequence of DNA repeated at different locations on different chromosomes.
anagenesis  The transformation of a single species over time.
anatomically modern Homo sapiens  The modern form of the human species, which dates back 130,000 years or more.
Anthropoidea (anthropoids)  The suborder of primates consisting of monkeys, apes, and humans.
anthropology  The science that investigates human biological and cultural variation and evolution.
anthropometrics  Measurements of the human body, skull, and face.
antibody  A substance that reacts to other substances invading the body (antigens).
antigen  A substance invading the body that stimulates the production of antibodies.
arboreal  Living in trees.
arboreal model  The view of primate origins that hypothesizes that stereoscopic vision and grasping hands first evolved as adaptations for moving around in the trees.
archaeology  The subfield of anthropology that focuses on cultural variation in prehistoric (and some historic) populations by analyzing the culture’s remains.
archaic humans  Specimens of Homo with brain size close to that of modern humans but with differently shaped skulls. There is considerable controversy over whether they are an earlier form of Homo sapiens or represent different species.
Ardipithecus ramidus  An early primitive hominid species from Africa dating between 5.8 million and 4.4 million years ago.
argon-argon dating  A chronometric dating method based on the half-life of radioactive argon that can be used with very small samples.
assortative mating  Mating between phenotypically similar or dissimilar individuals: for example, between two people with the same hair color.
Australopithecus  A genus of fossil hominid that lived between 4.2 million and 1 million years ago and is characterized by bipedal locomotion, small brain size, large face, and large teeth.
Australopithecus aethiopicus  The oldest robust australopithecine, dating to 2.5 million years ago in East Africa. It combines derived features seen in other robust australopithecines with primitive features seen in A. afarensis.
Australopithecus afarensis  A primitive hominid found in East Africa dating between 4 million and 3 million years ago. The teeth and postcranial skeleton show a number of primitive and apelike features.
Australopithecus africanus  A species of australopithecine dating between 3.3 million and 2.3 million years ago and found in South Africa. It is not as massive as the robust forms and may be an ancestor of the genus Homo.
Australopithecus anamensis  A hominid species that lived in East Africa between 4.2 million and 3.9 million years ago. It was a biped but had many primitive apelike features of the skull and teeth.
Australopithecus boisei  A very robust species of robust australopithecine dating between 2 million and 1.2 million years ago and found in East Africa.
Australopithecus garhi  A species of australopithecine dating to 2.5 million years ago in East Africa. It differs from other australopithecines in having large front and back teeth, although the back teeth are not specialized to the same extent as found in the robust australopithecines.
Australopithecus robustus  A species of robust australopithecine dating between roughly 2 million and 1.5 million years ago and found in South Africa.
B.P.  Before Present (1950), the internationally accepted form of designating past dates.
balancing selection  Selection for the heterozygote and against the homozygotes (the heterozygote is most fit). Allele frequencies move toward an equilibrium defined by the fitness values of the two homozygotes.
base  Chemical units (adenine, thymine, guanine, cytosine) that make up part of the DNA molecule and specify genetic instructions.
behavioral ecology  The study of behavior from an ecological and evolutionary perspective.
Bergmann’s rule  States that (1) among mammals of similar shape, the larger mammal loses heat less rapidly than the smaller mammal, and that (2) among mammals of similar size, the mammal with a linear shape will lose heat more rapidly than the mammal with a nonlinear shape.
biface  Stone tool with both sides worked, producing greater symmetry and efficiency.
bilateral symmetry  Symmetry in which the right and left sides of the body are approximately mirror images, a characteristic of vertebrates.
binocular stereoscopic vision  Overlapping fields of vision (binocular), with both sides of the brain receiving images from both eyes (stereoscopic), thereby providing depth perception.
biocultural approach  A method of studying humans that looks at the interaction between biology and culture in evolutionary adaptation.
biological anthropology  The subfield of anthropology that focuses on the biological evolution of humans and human ancestors, the relationship of humans to other organisms, and patterns of biological variation within and among human populations. Also referred to as physical anthropology.
biological species concept  A definition of species that focuses on reproductive capabilities, where organisms from different populations are considered to be in the same species if they naturally interbreed and produce fertile offspring.
biostratigraphy  A relative dating method in which sites can be assigned an approximate age based on the similarity of animal remains with other dated sites.
bipedal  Moving about on two legs. Unlike the movement of other bipedal animals such as kangaroos, human bipedalism is further characterized by a strid-ing motion.
blade  A stone tool characteristic of the Upper Paleolithic, defined as being at least twice as long as it is wide. Blade tools were made using an efficient and precise method.
brachiation  A method of movement that uses the arms to swing from branch to branch. Gibbons are brachiators.
breeding population  A group of organisms that tend to choose mates from within the group.
brow ridges  The large ridges of bone above the eye orbits, most noticeable in Homo erectus and archaic humans.
burin  A stone tool with a sharp edge that is used to cut and engrave bone.
canine  One of four types of teeth found in mammals. The canine teeth are located in the front of the jaw behind the incisors. Mammals normally use these teeth for puncturing and defense. Unlike most mammals, humans have small canine teeth that function like incisors.
carbon-14 dating  A chronometric dating method based on the half-life of carbon-14 that can be applied to organic remains such as charcoal dating back over the past 50,000 years or so.
carrying capacity  The maximum population size capable of being supported in a given environment.
Cenozoic era  The third and most recent geologic era of the Phanerozoic eon, dating roughly to the past 65 million years. The first primates appeared during the Cenozoic era.
cephalic index  A measure of cranial shape defined as the total length of a skull divided by the maximum width of the skull.
cerebrum  The area of the forebrain that consists of the outermost layer of brain cells. The cerebrum is associated with memory, learning, and intelligence.
Chordata  A vertebrate phylum consisting of organisms that possess a notochord at some period during their life.
chromosome  A long strand of DNA sequences.
chronometric dating  Method of dating fossils or sites that provides an estimate of the specific date (subject to probabilistic limits).
cladistics  A school of thought that stresses evolutionary relationships between organisms in forming biological classifications. Organisms are grouped together on the basis of the number of derived traits they share.
cladogenesis  The formation of one or more new species from another over time.
codominant  Both alleles affect the phenotype of a heterozygous genotype, and neither is dominant over the other.
comparative approach  Comparing human populations to determine common and unique behaviors or biological traits.
continental drift  The movement of continental land masses on top of a partially molten layer of the earth’s mantle. Because of continental drift, the relative location of the continents has changed over time.
convergent evolution  Independent evolution of a trait in rather distinct evolutionary lines. The development of flight in birds and certain insects is an example of convergent evolution.
cranial capacity  A measurement of the interior volume of the brain case measured in cubic centimeters (cc) and used as an approximate estimate of brain size.
crossing over  The exchange of DNA between chromosomes during meiosis.
cultural anthropology  The subfield of anthropology that focuses on variations in cultural behaviors among human populations.
culture  Behavior that is shared, learned, and socially transmitted.
cusp  A raised area on the chewing surface of a tooth.
demographic transition theory  A model of demographic change that states that as a population becomes economically developed a reduction in death rates (leading to population growth) will take place, followed by a reduction in birth rates.
dendrochronology  A chronometric dating method based on the fact that trees in dry climates tend to accumulate one growth ring per year. The width of the rings varies according to climate, and a sample can be compared with a master chart of tree rings over the past 10,000 years.
dental formula  A shorthand method of describing the number of each type of tooth in half of one jaw of a mammal. The dental formula consists of four numbers: I-C-PM-M, where I is the number of incisors, C is the number of canines, PM is the number of premolars, and M is the number of molars. When a mammal has a different number of teeth in the upper and lower jaws, two dental formulae are used.
derived trait  A trait that has changed from an ancestral state. The large human brain is a derived trait relative to the common ancestor of humans and apes.
dermatoglyphics  Measurements of finger and palm prints, including type classification and ridge counts.
developmental acclimatization  Changes in organ or body structure that occur during the physical growth of any organism.
diastema  A gap next to the canine teeth that allows space for the canine on the opposing jaw.
directional selection  Selection against one extreme in a continuous trait and/or selection for the other extreme.
distance curve  A measure of size over time, for example, a person’s height at different ages.
diurnal  Active during the day.
DNA (Deoxyribonucleic acid)  The molecule that provides the genetic code for biological structures and the means to translate this code.
dominance hierarchy  The ranking system within a society that indicates which individuals are dominant in social behaviors.
dominant allele  An allele that masks the effect of the other allele (which is recessive) in a heterozygous genotype.
electron spin resonance  A chronometric dating method that estimates dates from observation of radioactive atoms trapped in the calcite crystals pres-ent in a number of materials, such as bones and shells. This method is useful for dating sites back to roughly one million years.
electrophoresis  A laboratory method that uses electric current to separate proteins, allowing genotypes to be determined.
embryo  The stage of human prenatal life lasting from roughly two to eight weeks following conception, characterized by structural development.
emergent infectious disease  A newly identified infectious disease that has recently evolved.
endemic  A pattern of disease rate when new cases of a disease occur at a relatively constant but low rate over time.
endocast  A cast of the interior of the brain case used in the analysis of brain size and structure.
Eocene epoch  The second epoch of the Cenozoic era, dating roughly between 54 million and 34 million years ago. The first true primates, early prosimians, appeared during this epoch as well as the first anthropoid.
eon  The major subdivision of geologic time.
epidemic  A pattern of disease rate when new cases of a disease spread rapidly through a population.
epidemiologic transition  The increase in life expectancy and the shift from infectious to noninfectious disease as the primary cause of death.
epoch  Subdivision of a geological period.
era  Subdivision of a geological eon.
estrus  A time during the month when females are sexually receptive (also known as “heat”). Among primates, human and orangutan females lack an estrus period.
Eurasia  The combined land masses of Europe and Asia.
evolution  The transformation of species of organic life over long periods of time. Anthropologists study both the cultural and biological evolution of the human species.
evolutionary forces  Four mechanisms that can cause changes in allele frequencies from one generation to the next: mutation, natural selection, genetic drift, and gene flow.
exogamy  The tendency to choose mates from outside the local population.
exon  A section of DNA that codes for the amino acids that make up proteins. It is contrasted with an intron.
fetus  The stage of human prenatal growth from roughly eight weeks following conception until birth, characterized by further development and rapid growth.
fission-track dating  A chronometric dating method based on the number of tracks made across volcanic rock as uranium decays into lead.
fitness  An organism’s probability of survival and reproduction. Fitness is generally measured in terms of the different genotypes for a given locus.
foramen magnum  The large opening at the base of the skull where the spinal cord enters, which is located more under the skull in bipeds as compared to four-legged vertebrates.
founder effect  A type of genetic drift caused by the formation of a new population by a small number of individuals. The small size of the sample can cause marked deviations in allele frequencies from the origi-nal population.
gene  A DNA sequence that codes for a functional polypeptide or RNA product.
gene flow  A mechanism for evolutionary change resulting from the movement of genes from one population to another. Gene flow introduces new genes into a population and also acts to make populations more similar genetically to one another.
generalized structure  A biological structure adapted to a wide range of conditions and used in very general ways. For example, the grasping hands of humans are generalized structures allowing climbing, food gathering, toolmaking, and a variety of other functions.
genetic distance  An average measure of relatedness between populations based on a number of traits. Genetic distances are used for understanding effects of genetic drift and gene flow, which should affect all loci to the same extent.
genetic distance map  A picture that shows the genetic relationships between populations, based on genetic distance measures.
genetic drift  A mechanism for evolutionary change resulting from the random fluctuations of gene frequencies from one generation to the next, or from any form of random sampling of a larger gene pool.
genome  The total DNA sequence of an organism.
genotype  The genetic endowment of an individual from the two alleles present at a given locus.
genus  Groups of species with similar adaptations.
gradualism  A model of macroevolutionary change whereby evolutionary changes occur at a slow, steady rate over time.
grooming  The handling and cleaning of another individual’s fur or hair. In primates, grooming serves as a form of communication that soothes and provides reassurance.
half-life  The average length of time it takes for half of a radioactive substance to decay into another form.
Haplorhini (haplorhines)  One of two suborders of primates suggested to replace the prosimian/anthropoid suborders (the other is the strepsirhines). Haplorhines are primates without a moist nose (tarsiers, monkeys, apes, and humans).
Hardy-Weinberg equilibrium  In the absence of nonrandom mating and evolutionary forces, genotype and allele frequencies will remain the same from one generation to the next.
hemoglobin  The molecule in blood cells that transports oxygen.
heritability  The proportion of total variance in a trait due to genetic variation. This measure is not always the same; the actual value depends on the degree of environmental variation in any population.
heterodontic  Having different types of teeth. Mammals have four different types of teeth: incisors, canines, premolars, and molars.
heterozygous  The two alleles at a given locus are different.
holistic  Refers to the viewpoint that all aspects of existence are interrelated and important in understanding human variation and evolution.
homeobox gene  A group of regulatory genes that encode a sequence of 60 amino acids that regulate embryonic development. Homeobox genes subdivide from head to tail a developing embryo into different regions, which then form limbs and other structures. These genes are similar in many organisms, such as insects, mice, and humans.
homeostasis  In a physiologic sense, the maintenance of normal limits of body functioning.
homeotherm  Organism capable of maintaining a constant body temperature under most circumstances. Mammals are homeotherms.
home range  The size of the geographic area that is normally occupied and used by a social group.
hominid  Humans and humanlike ancestors since the time of divergence from the African apes. Some researchers advocate a somewhat different definition, including the African apes, and use the term "hominin" to refer to humans and their bipedal ancestors.
hominin  Under some taxonomic classifications, this term is used instead of "hominid" to refer to humans and humanlike ancestors.
hominoid  A superfamily of anthropoids consisting of apes and humans. Hominoids have a shoulder structure adapted for climbing and hanging, lack a tail, are generally larger than monkeys, and have the largest brain to body size ratio among primates.
Homo  A genus of hominids characterized by large brain size and dependence on culture as a means of adaptation.
homodontic  All teeth are the same.
Homo erectus  A species of genus Homo that arose 2 million years ago, first appearing in Africa and then spreading to parts of Asia and Europe.
Homo habilis  A species of early Homo from Africa between 2 million and 1.5 million years ago, with a brain size roughly half that of modern humans and a primitive postcranial skeleton.
homology  Similarity due to descent from a common ancestor.
homoplasy  Similarity due to independent evolution.
Homo rudolfensis  A species of early Homo from Africa roughly 2 million years ago, with a brain size somewhat larger than H. habilis.
homozygous  Both alleles at a given locus are identical.
horticulture  A form of farming in which only simple hand tools are used.
hypothesis  An explanation of observed facts. To be scientific, a hypothesis must be testable.
hypoxia  Oxygen starvation, which occurs frequently at high altitudes.
inbreeding  Mating between biologically related individuals.
incisor  One of four types of teeth found in mammals. The incisors are the chisel-shaped front teeth used for cutting, slicing, and gnawing food.
infanticide  The killing of infants.
infectious disease  A disease caused by the introduction of an organic foreign substance into the body. Such substances include viruses and parasites.
insectivore  An order of mammals adapted to insect eating.
intelligent design creationism  The idea that the biological world was created by an intelligent entity and did not arise from natural processes. This idea is somewhat different from that proposed by "creation scientists."
intron  A section of DNA that does not code for the amino acids that make up proteins. It is contrasted with an exon.
Kenyanthropus platyops  A species of early hominid in East Africa dating to 3.5 million years ago. This species combines a number of primitive features (small brain, jutting face) and derived features (small molars, flat face). Its evolutionary status is unclear.
kin selection  A concept used in sociobiological explanations of altruism. Sacrificial behaviors, for example, can be selected for if they increase the probability of survival of close relatives.
knuckle walking  A form of movement used by chimpanzees and gorillas that is characterized by all four limbs touching the ground, with the weight of the arms resting on the knuckles of the hands.
kwashiorkor  An extreme form of protein-calorie malnutrition resulting from a severe deficiency in proteins but not calories.
lactase persistence  The ability to produce the enzyme lactase after five years of age.
lactose intolerance  A condition characterized by diarrhea, cramps, and other intestinal problems resulting from the ingestion of milk.
larynx  Part of the vocal anatomy in the throat.
lemur  A prosimian found today on the island of Madagascar. Lemurs include both nocturnal and diurnal species.
life expectancy at birth  A measure of the average length of life for a newborn child.
life table  A compilation of the age distribution of a population that provides an estimate of the probability that an individual will die by a certain age, used to compute life expectancy.
linguistic anthropology  The subfield of anthropology that focuses on the nature of human language, the relationship of language to culture, and the languages of nonliterate peoples.
linkage  Alleles on the same chromosome are inherited together.
locus  The specific location of a gene or DNA sequence on a chromosome.
loris  Nocturnal prosimian found today in Asia and Africa.
Lower Paleolithic  The Lower Old Stone Age, a general term used to refer collectively to the stone tool technologies of Homo habilis / Homo rudolfensis and Homo erectus.
macroevolution  Long-term evolutionary change. The study of macroevolution focuses on biological evolution over many generations and on the origin of higher taxonomic categories, such as species.
major genes  Genes that have the primary effect on the phenotypic distribution of a complex trait. Additional variation can be due to smaller effects from other loci and/or environmental influences.
malnutrition  Poor nutrition, either from two much or too little food, or the improper balance of nutrients.
marasmus  An extreme form of protein-calorie malnutrition resulting from severe deficiencies in both proteins and calories.
mass extinction  Many species becoming extinct at about the same time.
meiosis  The creation of sex cells by replication of chromosomes followed by cell division. Each sex cell contains 50 percent of an individual’s chromosomes (one from each pair).
Mendelian genetics  The branch of genetics concerned with patterns and processes of inheritance. This field was named after Gregor Mendel, the first scientist to work out many of these principles.
Mendel’s Law of Independent Assortment  The segregation of any pair of chromosomes does not affect the probability of segregation for other pairs of chromosomes.
Mendel’s Law of Segregation  Sex cells contain one of each pair of alleles.
menopause  The permanent cessation of menstrual cycles.
Mesozoic era  The second geologic era of the Phanerozoic eon, dating roughly between 245 million and 65 million years ago, when the first mammals and birds appeared.
messenger RNA  The form of RNA that transports the genetic instructions from the DNA molecule to the site of protein synthesis.
microevolution  Short-term evolutionary change. The study of microevolution focuses on changes in allele frequencies from one generation to the next.
microsatellite DNA  Repeated short sequences of DNA; the number of repeats is highly variable.
Middle Paleolithic  The Middle Old Stone Age, a general term used to refer collectively to the stone tool technologies of archaic humans.
Miocene epoch  The fourth epoch of the Cenozoic era, dating between 23 million and 5 million years ago. The first apes evolved during the Miocene. The first hominids are dated to the Late Miocene.
mitochondrial DNA  A small amount of DNA that is located in the mitochondria of cells. Mitochondrial DNA is inherited only through the mother.
mitosis  The process of replication of chromosomes in body cells. Each cell produces two identical copies.
molar  One of four types of teeth found in mammals. The molars are back teeth used for crushing and grinding food.
molecular dating  The application of methods of genetic analysis to estimate the sequence and timing of divergent evolutionary lines.
monogamous family group  Social structure in which the primary social group consists of an adult male, an adult female, and their immature offspring.
monogamy  An exclusive sexual bond between an adult male and an adult female for a long period of time.
monosymy  A condition in which one chromosome rather than a pair is present in body cells.
morphology  The physical structure of organisms.
Mousterian tradition  The prepared-core stone tool technology of the Neandertals.
multimale/multifemale group  A type of social structure in which the primary social group is made up of several adult males, several adult females, and their offspring.
multiregional evolution model  The hypothesis that modern humans evolved throughout the Old World as a single species after the first dispersion of Homo erectus out of Africa. According to this view, the transition from Homo erectus to archaic humans to modern Homo sapiens occurred within a single evolutionary line throughout the Old World.
multivariate analysis  The analysis of human biological variation that considers the interrelationships of several traits at a time.
mutation  A mechanism for evolutionary change resulting from a random change in the genetic code; the ultimate source of all genetic variation. Mutations must occur in sex cells to cause evolutionary change.
nasal index  A measure of the shape of the nasal opening, defined as the width of the nasal opening divided by the height.
natural increase  Number of births minus the number of deaths.
natural selection  A mechanism for evolutionary change favoring the survival and reproduction of some organisms over others because of their biological characteristics.
Neandertals  A population of archaic humans that lived in Europe and the Middle East, dating between 150,000 and 28,000 years ago.
nocturnal  Active during the night.
noninfectious disease  A disease caused by factors other than the introduction of an organic foreign substance into the body.
nonrandom mating  Patterns of mate choice that influence the distributions of genotype and phenotype frequencies. Nonrandom mating does not lead to changes in allele frequencies.
notochord  A flexible internal rod that runs along the back of an animal. Animals possessing a notochord at some period in their life are known as chordates.
occipital bun  The protruding rear region of the skull, a feature commonly found in Neandertals.
odontometrics  Measurements of the size of teeth.
Oldowan tradition  The oldest known stone tool culture.
Oligocene epoch  The third epoch of the Cenozoic era, dating roughly between 34 million and 23 million years ago, when there was an adaptive radiation of anthropoids.
Orrorin tugenensis  An early primitive hominid species from Africa dating to the late Miocene (6 Ma).
orthogenesis  A discredited idea that evolution would continue in a given direction because of some vaguely defined "force."
outgroup  A group used for comparison in cladistic analyses to determine whether the ancestral state of a trait is primitive or derived.
Paleocene epoch  The first epoch of the Cenozoic era, dating roughly between 65 million and 54 million years ago. The primate-like mammals lived during the Paleocene.
paleoecology  The study of ancient environments.
paleomagnetic reversal  A method of dating sites based on the fact that the earth’s magnetic field has shifted back and forth from the north to the south in the past at irregular intervals.
paleopathology  The study of disease in prehistoric populations based on analysis of skeletal remains and archaeological evidence.
paleospecies  Species identified from fossil remains based on their physical similarities and differences relative to other species.
Paleozoic era  The first geologic era of the Phanerozoic eon, dating roughly between 545 million and 245 million years ago, when the first vertebrates appeared.
palynology  The study of fossil pollen. Palynology allows prehistoric plant species to be identified.
pandemic  A widespread epidemic that affects a large geographic area, such as a continent.
parallel evolution  Independent evolution of a trait in closely related species. One example might be the parallel development of large back teeth in several hominid species.
parental investment  A concept used in sociobiological models that describes parental behaviors that increase the probability that offspring will survive.
period  Subdivision of a geologic era.
Phanerozoic eon  The past 545 million years.
phenetics  A school of thought that stresses the over-all physical similarities among organisms in forming biological classifications.
phenotype  The observable appearance of a given genotype in the organism. The phenotype is determined by the relationship of the two alleles at a given locus, the number of loci, and often environmental influences as well.
placenta  An organ that develops inside a pregnant placental mammal that provides the fetus with oxygen and food and helps filter out harmful substances.
plasticity  The ability of an organism to respond physiologically or developmentally to environmental stress.
pleiotropy  A single allele that has multiple effects on an organism.
Pleistocene epoch  The sixth epoch of the Cenozoic era, dating from 1.7 million to 0.01 million years ago.
Pliocene epoch  The fifth epoch of the Cenozoic era, dating from 5 million to 1.7 million years ago.
polyandrous group  A rare type of primate social structure, consisting of a small number of adult males, one reproductively active adult female, and their offspring. Other adult females may belong to the group but are not reproductively active.
polyandry  In humans, a form of marriage in which a wife has several husbands. In more general terms, it refers to an adult female having several mates.
polygamy  A sexual bond between an adult male and an adult female in which either individual may have more than one mate at the same time.
polygenic  A complex genetic trait affected by two or more loci.
polygyny  In humans, a form of marriage in which a husband has several wives. In more general terms, it refers to an adult male having several mates.
polymorphism  A discrete genetic trait in which there are at least two alleles at a locus having frequencies greater than 0.01.
population pyramid  A diagram of the age-sex structure of a population.
postcranial  Referring to that part of the skeleton below the skull.
postnatal  The period of life from birth until death.
postorbital bar  The bony ring that separates the eye orbit from the back of the skull. The postorbital bar is a primate characteristic.
postorbital constriction  The narrowness of the skull behind the eye orbits, a characteristic of early hominids.
potassium-argon dating  A chronometric dating method based on the half-life of radioactive potassium (which decays into argon gas) that can be used to date volcanic rock older than 100,000 years.
Precambrian eon  The eon from the earth’s beginning (4.6 billion years ago) until 545 million years ago. During this eon, single-celled and simple multicelled organisms first evolved.
prehensile  Capable of grasping. Primates have prehensile hands and feet, and some primates (certain New World monkeys) have prehensile tails.
premolar  One of four types of teeth found in mammals. The premolars are back teeth used for crushing and grinding food.
prenatal  The period of life from conception until birth.
prepared-core method  An efficient method of stone tool manufacture in which a stone core is prepared and then finished tools are removed from it.
primary African origin model  A variant of the multiregional evolution model of the origin of modern humans that suggests most of the transition from archaic to modern humans took place first in Africa and then spread throughout the rest of the species across the Old World by gene flow.
primates  The order of mammals that has a complex of characteristics related to an initial adaptation to life in the trees, including binocular stereoscopic vision and grasping hands. The primates include prosimians, monkeys, apes, and humans.
primitive trait  In biological terms, a trait that has not changed from an ancestral state. The five digits of the human hand and foot are primitive traits inherited from earlier vertebrate ancestors.
Proconsul  A genus of fossil hominoid that lived in Africa between 23 million and 17 million years ago. Though classified as apes, this genus also shows a number of monkey characteristics. It most probably represents one of the first forms to evolve following the divergence of the monkey and ape lines.
Prosimii (prosimians)  The suborder of primates that are biologically primitive compared to anthropoids.
protein-calorie malnutrition  A group of nutritional diseases resulting from inadequate amounts of protein and/or calories. Protein-calorie malnutrition is a severe problem in less developed countries today.
punctuated equilibrium  A model of macroevolutionary change in which long periods of little evolutionary change (stasis) are followed by relatively short periods of rapid evolutionary change.
quadrupedal  A form of movement in which all four limbs are of equal size and make contact with the ground, and the spine is roughly parallel to the ground. Monkeys are typical quadrupedal primates.
race  A group of populations sharing certain biological traits that make them distinct from other groups of populations. In practice, the concept of race is very difficult to apply to patterns of human variation.
recessive allele  An allele whose effect is masked by the other allele (which is dominant) in a heterozygous genotype.
recombination  The production of new combinations of DNA sequences caused by exchanges of DNA during meiosis.
regional coalescence model  A variant of the multiregional evolution model of the origin of modern humans that suggests the transition from archaic to modern humans resulted from the coalescence of genetic and anatomic changes that took place in different places at different times, all mixing together to produce modern humans.
regional continuity  The appearance of similar traits within a geographic region that remain over a long period of time.
regulatory gene  Gene that codes for the regulation of biological processes such as growth and development.
relative dating  Comparative method of dating fossils and sites that provides an estimate of the older find but not a specific date.
remergent infectious disease  Infectious disease that had previously been reduced but that increases in frequency when microorganisms evolve resistance to antibiotics.
reproductive isolation  The genetic isolation of populations that may render them incapable of producing fertile offspring.
restriction fragment length polymorphism (RFLP)  A genetic trait defined in terms of the length of DNA fragments produced when certain enzymes cut the DNA sequence.
Rhesus incompatibility  A condition in which a pregnant woman and her fetus have incompatible Rhesus blood group phenotypes.
RNA (Ribonucleic acid)  The molecule that functions to carry out the instructions for protein synthesis specified by the DNA molecule.
robust australopithecines  Species of Australopithecus that had very large back teeth, cheekbones, and faces, among other anatomical adaptations to heavy chewing. They lived in Africa between 2.5 million and 1.2 mil-lion years ago. Three species are generally recognized: A. aethiopicus, A. robustus, and A. boisei. Some anthropologists suggest that they be given their own genus name—Paranthropus.
sagittal crest  A ridge of bone running down the center of the top of the skull that serves to anchor chewing muscles.
savanna  An environment consisting of open grasslands in which food resources tend to be spread out over large areas.
secular change  A change in the average pattern of growth or development in a population over several generations.
sedentary  Settled in one place throughout most or all of the year.
sexual dimorphism  The average difference in body size between adult males and adult females. Primate species with sexual dimorphism in body size are characterized by adult males being, on average, larger than adult females.
sickle cell allele  An allele of the hemoglobin locus. Individuals homozygous for this allele have sickle cell anemia.
sickle cell anemia  A genetic disease that occurs in a person homozygous for the sickle cell allele, which alters the structure of red blood cells.
single-nucleotide polymorphisms (SNPs)  Specific positions in a DNA sequence that differ at one base. For example, the DNA sequences CCTGAA and CCCGAA differ in the third position—one sequence has the base T and the other the base C.
social structure  The composition of a social group and the way it is organized, including size, age structure, and number of each sex in the group.
sociobiology  The study of behavior from an evolutionary perspective, particularly the role of natural selection.
solitary group  The smallest primate social group, consisting of the mother and her dependent offspring.
specialized structure  A biological structure adapted to a narrow range of conditions and used in very specific ways. For example, the hooves of horses are specialized structures allowing movement over flat terrain.
speciation  The origin of a new species.
species  A group of populations whose members can interbreed naturally and produce fertile offspring.
stabilizing selection  Selection against extreme values, large or small, in a continuous trait.
stratigraphy  A relative dating method based on the fact that older remains are found deeper in the earth (under the right conditions). This method makes use of the fact that a cumulative buildup of the earth’s surface takes place over time.
Strepsirhini (strepsirhines)  One of two suborders of primates suggested to replace the prosimian/anthropoid suborders (the other is the haplorhines). Strepsirhines are primates that have a moist nose (lemurs and lorises).
stress  Any factor that interferes with the normal limits of operation of an organism.
suspensory climbing  The ability to raise the arms above the head and hang on branches and to climb in this position. Hominoids are suspensory climbers.
taphonomy  The study of what happens to plants and animals after they die. Taphonomy helps in determining reasons for the distribution and condition of fossils.
tarsier  Nocturnal prosimian found today in Indonesia. Unlike other prosimians, tarsiers lack a moist nose.
taxonomy  The science of describing and classifying organisms.
terrestrial  Living on the ground.
territory  A home range that is actively defended.
theistic evolution  The belief that God operates through the natural process of evolution.
theory  A set of hypotheses that have been tested repeatedly and that have not been rejected. This term is sometimes used in a different sense in social science literature.
therapsid  An early group of mammal-like reptiles; therapsids were the ancestors of later mammals.
thermoluminescence  A chronometric dating method that uses the fact that certain heated objects accumu-late trapped electrons over time, which allows the date when the object was initially heated to be determined.
transfer RNA  A free-floating molecule that is attracted to a strand of messenger RNA, resulting in the synthesis of a protein chain.
trephination  Surgery involving the removal of a section of bone from the skull.
trisomy  A condition in which three chromosomes rather than a pair occur. Down syndrome is caused by trisomy by the addition of an extra chromosome to the 21st chromosome pair.
uni-male group  Social structure in which the primary social group consists of a single adult male, several adult females, and their offspring.
univariate analysis  The analysis of human biological variation focusing on a single trait at a time.
Upper Paleolithic  The Upper Old Stone Age, a general term used to collectively refer to the stone tool technologies of anatomically modern Homo sapiens.
variation  The differences that exist among individuals or populations. Anthropologists study both cultural and biological variation.
vasoconstriction  The narrowing of blood vessels, which reduces blood flow and heat loss.
vasodilation  The opening of the blood vessels, which increases blood flow and heat loss.
velocity curve  A measure of the rates of change in growth over time.
Vertebrata  A subphylum of the phylum Chordata, defined by the presence of an internal, segmented spinal column and bilateral symmetry.
visual predation model  The view of primate origins that hypothesizes that stereoscopic vision and grasping hands first evolved as adaptations for hunting insects along branches.
zoonose  A disease transmitted directly to humans from other animals.
zygomatic arch  The cheekbone, formed by the connection of the zygomatic and temporal bones on the side of the skull.
zygote  A fertilized egg.





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