abnormal hemoglobin Hemoglobin altered so that it is less efficient in binding to and carrying oxygen.

Acheulian complex The culture associated with H. erectus, including hand axes and other types of stone tools; more refined than the earlier Oldowan tools.

adapids Euprimates of the Eocene that were likely ancestral to modern lemurs and possibly ancestral to anthropoids.

Adapis A genus of adapids from the Eocene.

adaptations Changes in physical structure, function, or behavior that allow an organism or species to survive and reproduce in a given environment.

adaptive radiation The diversification of an ancestral group of organisms into new forms that are adapted to specific environmental niches.

adenine One of four nitrogen bases that make up DNA and RNA; it pairs with thymine in DNA molecules and uracil in RNA molecules.

adenosine triphosphate (ATP) An important cellular molecule, created by the mitochondria and carrying the energy necessary for cellular functions.

admixture The exchange of genetic material between two or more populations.

adult stage The third stage of life, involving the reproductive years and senescence.

Aegyptopithecus A propliopithecid genus from the Oligocene, probably ancestral to catarrhines; the largest primate found in the Fayum, Egypt.

aging The process of maturation.

allele One or more alternative forms of a gene.

Allen's Rule The principle that an animal's limb lengths are heat-related; limbs are longer in hot environments and shorter in cold environments.

altruistic Refers to a behavior that benefits others while being a disadvantage to the individual.

ameloblasts Cells that produce and secrete the material that becomes tooth enamel.

amino acid dating An absolute dating method for organic remains such as bone or shell, in which the amount of change in the amino acid structure is measured.

amino acids Organic molecules combined in a specific sequence to form a protein.

anatomical Pertaining to an organism's physical structure.

angiosperm radiation hypothesis The proposition that certain primate traits, such as visual acuity, occurred in response to the availability of fruit and flowers following the spread of angiosperms.

anthropogenic Refers to any effect caused by humans.

anthropology The study of humankind, viewed from the perspective of all people and all times.

anthropometry The study of the sizes and proportions of the human body.

antibodies Molecules that form as part of the primary immune response to the presence of foreign substances; they attach to the foreign antigens.

anticodons Sequences of three nitrogen bases carried by tRNA, they match up with the complementary mRNA codons and each designate a specific amino acid during protein synthesis.

antigens Substances, such as bacteria, foreign blood cells, and enzymes, that stimulate the immune system's antibody production.

Apidium A parapithecid genus from the Oligocene, possibly ancestral to anthropoids.

arboreal Tree-dwelling; adapted to living in the trees.

arboreal adaptation A suite of physical traits that enable an organism to live in trees.

arboreal hypothesis The proposition that primates' unique suite of traits is an adaptation to living in trees.

Archaeoindris An extinct genus of lemurs found in Madagascar.

Archaeolemur An extinct genus of lemurs found in Madagascar.

archaeology The study of historic or prehistoric human populations through the analysis of material remains.

Ardipithecus kadabba An early pre-australopithecine species from the late Miocene to the early Pliocene; shows evidence of a perihoning complex, a primitive trait intermediate between apes and modern humans.

Ardipithecus ramidus A later pre-australopithecine species from the late Miocene to the early Pliocene; shows evidence of both bipedalism and arboreal activity but no indication of the primitive perihoning complex.

artifacts Material objects from past cultures.

Australopithecus aethiopicus An early robust australopithecine from East Africa, with the hallmark physical traits of large teeth, large face, and massive muscle attachments on the cranium.

Australopithecus afarensis An early australopithecine from East Africa that had a brain size equivalent to a modern chimpanzee's and was thought to be a direct human ancestor.

Australopithecus africanus A gracile australopithecine from South Africa that was contemporaneous with A. aethiopicus, A. garhi, and A. boisei and was likely ancestral to A. robustus.

Australopithecus anamensis The oldest species of australopithecine from East Africa and a likely ancestor to A. afarensis.

Australopithecus boisei Formerly known as Zinjanthropus boisei; a later robust australopithecine from East Africa that was contemporaneous with A. robustus and A. africanus and had the robust cranial traits, including large teeth, large face, and heavy muscle attachments.

Australopithecus garhi A late australopithecine from East Africa that was contemporaneous with A. africanus and A. aethiopicus and was the likely ancestor to the Homo lineage.

Australopithecus (or Kenyanthropus) platyops An australopithecine from East Africa that had a unique flat face and was contemporaneous with A. afarensis.

Australopithecus robustus A robust australopithecine from South Africa that may have descended from A. afarensis, was contemporaneous with A. boisei, and had the robust cranial traits of large teeth, large face, and heavy muscle attachments.

autosomes All chromosomes, except the sex chromosomes, that occur in pairs in all somatic cells (not the gametes).