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Glossary


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  The stone tool culture 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.
affiliative  Friendly behaviors that promote social bonds.
African replacement model  The hypothesis that modern humans evolved as a new species in Africa 200,000 years ago and then spread throughout the Old World, replacing preexisting 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.
agonistic  Unfriendly social relationships.
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.
alloparent  An individual that cares for an infant but is not a biological parent.
Alu insertions  A sequence of DNA repeated at different locations on different chromosomes.
anagenesis  The transformation of a single species over time.
anatomically modern humans  The modern form of the human species, which dates back 200,000 years.
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.
archaeology  The subfield of anthropology that focuses on cultural variations in prehistorical and historical populations by analyzing the culture's remains.
Archean eon  The second geologic eon, dating from 3800 to 2500 Ma, characterized by the appearance of the first single-celled organisms.
Ardipithecus kadabba  An early primitive hominin with very apelike teeth from Africa dating between 5.8 million and 5.2 million years ago.
Ardipithecus ramidus  An early primitive hominid species from Africa dating between 5.8 million and 4.4 million years ago.
argon-argon dating  A variation of potassium-argon dating that can be applied to very small samples of volcanic rock.
assimilation model  The hypothesis that modern human anatomy arose first in Africa as a change within a species, and then spread through gene flow to populations outside of Africa. The gene pool of the non- African archaic populations was thus assimilated into an expanding population of modern humans out of Africa.
assortative mating  Mating between phenotypically similar or dissimilar individuals—for example, between two people with the same hair color.
Australopithecus  A genus of fossil hominin 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 australopith, dating to 2.5 million years ago in East Africa. It combines derived features seen in other robust australopith with primitive features seen in A. afarensis.
Australopithecus afarensis  A primitive hominin found in East Africa, dating between 3.7 million and 3.0 million years ago. The teeth and postcranial skeleton show a number of primitive and apelike features.
Australopithecus africanus  An early hominin, 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 hominin 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 australopith, dating between 2.4 million and 1.4 million years ago and found in East Africa.
Australopithecus garhi  An early hominin, dating to 2.5 million years ago in East Africa. It differs from other australopiths in having large front and back teeth, although the back teeth are not specialized to the same extent as found in the robust australopiths.
Australopithecus robustus  A species of robust australopith, dating between roughly 2 million and 1.4 million years ago and found in South Africa.
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 that focuses on the adaptive value 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  A 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 race  A group of populations sharing certain biological traits that distenguish them from other groups of populations. In practice, the biological concept of race has been difficult to apply to human populations.
biological species concept  A definition of species that focuses on reproductive capabilities, where by 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 to those from 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 striding 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.
B.P.  Before Present (1950), the internationally accepted form of designating past dates.
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, very noticeable in Homo erectus.
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.
Carpolestes simpsoni  A species of primate-like mammal that had some derived primate traits, such as a grasping foot and an opposable big toe. This species is intermediate in many respects between primitive primate-like mammals and true primates.
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 to the last 65.5 Ma. Primate and human evolution occurred 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  A method of dating fossils or sites that provides an estimate of the specific date (subject to probabilistic limits).
chronospecies  Labels given to different points in the evolutionary lineage of a single species over time. As a species changes over time, the different stages are labeled as chronospecies to recognize the biological changes that have taken place.
civilation  A large, state-level society characterized by large population size, high population density, Urbanization, social stratification, food and labor surpluses, monumental architecture, and record keeping.
cladistics  A school of thought that stresses evolutionary relationships between organisms based on derived homologous traits.
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 stating 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.
Dryopithecus  A genus of fossil ape that lived in Europe during the Middle and Late Miocene. This form and the related form Ouranopithecus have cranial traits that suggest one may have been an ancestor of African apes and humans.
electron spin resonance (ESR)  A chronometric dating method that estimates dates from observation of radioactive atoms trapped in the calcite crystals present in a number of materials, such as bones and shells. This method is useful for dating sites back to roughly 1 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 between 55.8 million and 33.9 million years ago. The first true primates, primitive prosimians, appeared during the Eocene.
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 geologic period.
era  Subdivision of a geologic eon.
estrus  A time during the month when females are sexually receptive.
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.
evolutionary systematics  A school of thought that stresses the overall similarity of all (primitive and derived) homologous traits in classification.
exon  A section of DNA that codes for the amino acids that make up proteins. It is contrasted with an intron.
experimental archaeology  A field of archaeology that involves the study of the manufacture and use of tools in order to learn how they were made and used by people in the past.
fetus  The stage of human prenatal growth from roughly eight weeks following conception until birth, characterized by further development and rapid growth.
fission-fusion  A primate society where the population splits into smaller subgroups at times (fission) and then later reunited (fusion). The process is affected by distribution of food resources.
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.
fluorine dating  A relative dating method based on the accumulation of fluorine in a bone that tells if two bones from a site are of the same age.
foramen magnum  The large opening at the base of the skull where the spinal cord enters. This opening is located more toward the center of the skull in hominins, who are bipeds, so that the skull sits atop the spine.
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 original 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 to understand the 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. In primates, grooming serves as a form of communication that soothes and provides reassurance.
Hadean eon  The first geologic eon, dating from 4600 to 3800 Ma, which occurred before the oldest fossil evidence of life.
half-life  The average length of time it takes for half of a radioactive substance to decay into another form.
haplogroup  A set of related haplotypes that share similar mutations.
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).
haplotype  A combination of genes or DNA sequences that are inherited as a single unit.
Hardy-Weinberg equilibrium  A mathematical statement whereby 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.
HLA (human leukocyte antigen) system  A diverse genetic system consisting of linked loci on chromosome 6 that control autoimmune response.
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.
homeother  An 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  A family (Hominidae) within the hominoids. In recent years, this family has been defined as including humans and the great apes (orangutan, gorilla, chimpanzee, and bonobo). Some scientists still use a more traditional definition that refers only to humans and their humanlike ancestors.
hominin  Humans and their ancestors since the time of divergence from the common ancestor of humans, chimpanzees, and bonobos.
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 the genus Homo that arose 1.8 million years ago in Africa and then spread to parts of Asia and Europe.
Homo ergaster  A species suggested by some anthropologists consisting of the early African specimens of Homo erectus.
Homo floresiensis  The species name given to a very small hominin that lived in Indonesia in recent times, and is suggested by some to be a dwarf species of Homo erectus.
Homo habilis  A species of early Homo from Africa that lived between 2 million (or earlier) and 1.6 million years ago, with a brain size roughly half that of modern humans and a primitive postcranial skeleton.
Homo heidelbergensis  A species of archaic human, with a brain size close to that of modern humans but a larger, less modern face, that lived in Africa, Europe, and Asia between 800,000 and 200,000 years ago.
Homo rudolfensis  A species of early Homo from Africa that lived between 2.4 million and 1.6 million years ago, with a brain size somewhat larger than Homo habilis but with larger back teeth and a broader face.
Homo sapiens  Modern humans.
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 Homo 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.
intron  A section of DNA that does not code for the amino acids that make up proteins. It is contrasted with an exon.
island dwarfism  The process by which natural selection favors smaller body size on an island with limited resources, leading to dwarfed species.
isolation by distance  A model predicting that the genetic distance between populations will increase as the geographic distance between them increases.
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  The concept that altruistic behavior can be selected for if it increases 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 age 5.
lactose intolerance  A condition characterized by diarrhea, cramps, and other intestinal problems resulting from the ingestion of milk.
lemur  A prosimian found today on the island of Madagascar. Lemurs include both nocturnal and diurnal species.
Levallois technique  A method of making stone tools in which a stone core is prepared in such a way that finished tools can be removed from it by a final blow. Also known as the prepared-core method.
life expectancy at birth  A measure of the average length of life for a newborn child.
life history theory  The study of how characteristics of an organism's life cycle affects reproduction, focusing on tradeoffs between energy expended for numbers and fitness of offspring.
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  A nocturnal prosimian found today in Asia and Africa.
Lower Paleolithic  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 too 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  A law stating that the segregation of any pair of chromosomes does not affect the probability of segregation for other pairs of chromosomes.
Mendel's Law of Segregation  A law stating that 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 from 251 to 65.5 Ma, when the dinosaurs were dominant and when 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  A general term used to refer collectively to the stone tool technologies of Homo heidelbergensis and the Neandertals.
Middle Pleistocene  A geologic stage of the Pleistocene epoch that lasted from 781,000 to 126,000 years ago.
Miocene epoch  The fourth epoch of the Cenozoic era, dating between 23.0 million and 5.3 million years ago. Several adaptive radiations of hominoids occurred during the Miocene, and the oldest known possible hominins appeared during 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.
monogamy  An exclusive sexual bond between an adult male and an adult female for a long period of time.
monosomy  A condition in which one chromosome rather than a pair is present in body cells.
Morotopithecus  A genus of fossil ape that lived in Africa 20 million years ago and whose postcranial anatomy was similar in a number of ways to living apes.
morphology  The physical structure of organisms.
Mousterian tradition  The prepared-core stone tool technology of the Neandertals.
multimale/multifemale group  The most common type of social group in nonhuman primates; it consists of several adult males, several adult females, and their immature 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.
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  The 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 humans that lived in Europe and the Middle East between about 130,000 and 28,000 years ago. Debate continues about whether they are a subspecies of Homo sapiens or a separate species and to what extent they contributed to the ancestry of humans today.
nocturnal  Active during the night.
noninfectious diseas  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.
nuclear DNA  The DNA that is contained in the nucleus of the cell.
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 between 33.9 million and 23.0 million years ago. Anthropoids underwent an adaptive radiation during the Oligocene.
one-female/multimale group  A social structure in which the primary social group consists of a single adult female, several adult males, and their immature offspring.
one-male/multifemale group  A social structure in which the primary social group consists of a single adult male, several adult females, and their immature offspring.
one-male/one-female group  A social structure in which the primary social group consists of a single adult male, a single adult female, and their immature offspring.
Orrorin tugenensis  An early primitive, possibly 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.
paleoanthropology  The study of primate and human evolution.
Paleocene epoch  The first epoch of the Cenozoic era, dating between 65.5 million and 55.8 million years ago. The primate-like mammals appeared during the Paleocene.
paleoecology  The study of ancient environments.