Glossary of Biological and Paleontological Terms

(Compiled by Charles J Vella, PhD: thanks to Wikipedia, Smithsonian, etc.)

Acquired trait: A phenotypic characteristic, acquired during growth and development, that is not genetically based and therefore cannot be passed on to the next generation (for example, the large muscles of a weightlifter).

Adaptation: An adaptation is a feature produced by natural selection for its current function.

Adaptive radiation: The diversification, over evolutionary time, of a species or group of species into several different species or subspecies that are typically adapted to different ecological niches (for example, Darwin's finches).

Advanced (synonym: derived; opposite: primitive): In phylogenetic studies, an organism or character further removed from an evolutionary divergence than a more primitive one.

Allele: A known variation (version) of a particular gene

Allen's Rule: Within species of warm-blooded animals (birds + mammals) those populations living in colder environments will tend to have shorter appendages than populations in warmer areas.

Allometry: The relation between the size of an organism and the size of any of its parts. For example, an allometric relation exists between brain size and body size, such that (in this case) animals with bigger bodies tend to have bigger brains.

Allopatric speciation: Speciation following geographical isolation of subpopulations of the species.

Analogous structures: Structures in different species that look alike or perform similar functions (e.g., the wings of butterflies and the wings of birds) that have evolved convergently but do not develop from similar groups of embryological tissues, and that have not evolved from similar structures known to be shared by common ancestors. Contrast with homologous structures.

Ancestral homology: Homology that evolved before the common ancestor of a set of species, and which is present in other species outside that set of species. Compare with derived homology.

Anthropoid: A member of the group of primates made up of monkeys, apes, and humans.

Apomorphy: a characteristic that is different form the form of an ancestor, i.e., an innovation, of use in determining membership in a clade. In other words, it is an apomorphy shared by members of a monophyletic group, and thus assumed to be

present in their most recent common ancestor. A derived trait is an apomorphy, which means a trait that has changed since the time of a common ancestor.

Artificial selection: The process by which humans breed animals and cultivate crops to ensure that future generations have specific desirable characteristics. In artificial selection, breeders select the most desirable variants in a plant or animal population and selectively breed them with other desirable individuals

Australopithecus: The extinct genus of Plio-Pleistocene hominids found in South and East Africa. The evolutionary link between apes and humans.

Australopithecine: A group of bipedal hominid species belonging to the genus Australopithecus that lived between 4.2 and 1.4 mya.

Australopithecus afarensis: An early australopithecine species that was bipedal; known fossils date between 3.6 and 2.9 mya (for example, Lucy).

Bergmann's Rule: Northern races of mammals and birds tend to be larger than Southern races of the same species.

Biological species concept: The concept of species, according to which a species is a set of organisms that can interbreed among each other. Compare with cladistic species concept, ecological species concept, phenetic species concept, and recognition species concept.

Bipedal: Habitually walking upright on two legs

Bottleneck: A drastic reduction in the population size followed by an expansion. This often results in altered gene pool as a result of subsequent genetic drift.

Brow ridge: Bony ridge above the eye sockets

Catalogue number: Sometimes also called a field number, this is the number given a fossil by the researcher during the time of discovery. Catalogue numbers usually consist of a location abbreviation (i.e. 'OH' standing for 'Olduvai Hominid') followed by a number assigned to the fossil, normally in the order that it was found. So OH5 is the fifth hominid that was found at Olduvai Gorge.

Catarrhini: One of the two divisions (suborder) of Primates containing the old world monkeys and apes (extinct and extant). The other division is Platyrrhini (new world monkeys).

Clade: A clade (from Ancient Greek: κλάδος, klados, "branch") is a group of organisms that consists of a common ancestor and all its lineal descendants, and represents a single "branch" on the "tree of life". All descendants of any given species. A single whole branch of a phylogeny. Synonym of monophyletic group.

Cladistics: Cladistics (from Greek κλάδος, klados, i.e., "branch") is an approach to biological classification in which organisms are categorized based on shared derived characteristics that can be traced to a group's most recent common ancestor and are not present in more distant ancestors. Therefore, members of a group are assumed to share a common history and are considered to be closely related. In terms of strict

cladistical analysis, the age of the fossils does not matter. Cladistics establishes evolutionary relationships strictly by grouping organisms according to their shared-derived characteristics. In the case of paleontology, the characteristics are almost always morphological, but in living organisms, the traits may be behavioral or genetic as well.

Cladogram: A branching diagram that illustrates hypotheses about the evolutionary relationships among groups of organisms. Cladograms can be considered as a special type of phylogenetic tree that concentrates on the order in which different groups branched off from their common ancestors. A cladogram branches like a family tree, with the most closely related species on adjacent branches.

Co-evolution: Joint evolution of two unrelated species that have a close ecological relationship resulting in reciprocal adaptations as happens between host and parasite, and plant and insect.

Convergent evolution: independent evolution of similar features in species of different lineages. Convergent evolution creates analogous structures that have similar form or function but were not present in the last common ancestor of those groups. Same as homoplasy. Evolution of two or more different lineages towards similar morphology due to similar adaptive pressures. Examples of convergence are: fins or fin-like structures in fish, cuttlefish and whales; extreme similarity in alarm calls by five small birds; endothermy in dogs and ducks, wings of butterflies and birds.Coprolite: The fossilized waste (dung; fecies) matter of animals.

Core: In stone tool terminology, a source stone reduced in size by the intentional removal of flakes

Cranial: Refers to a bone of the cranium, which is part of the skull (but does not include the mandible).

Creationism: The religious doctrine that all living things on Earth were created separately, in more or less their present form, by a supernatural creator, as stated in the Bible; the precise beliefs of different creationist groups vary widely.

Darwinian evolution: Evolution by the process of natural selection acting on random variation.

Darwinism: Darwin's theory that species originated by evolution from other species and that evolution is mainly driven by natural selection. Differs from neo-Darwinism mainly in that Darwin did not know about Mendelian inheritance.

Dental microwear: Dental microwear is the study of the microscopic wear on a tooth's surface that occurred as a direct result of use (chewing). Dental microwear studies look for tooth scratches and pits that occur on teeth predominantly through chewing, and can provide evidence of what an individual ate in the past.

Derived: A derived character is a character that is derived from an ancestral character over evolutionary history; a newer characteristic; in phylogenetics, a derived character of a clade that has been inherited from a common ancestor and distinguishes the clade from other potentially related organisms is called a "synapomorphy," a shared ("syn") character that sets the clade apart ("apo")

Diastema: A diastema is space between two teeth. In paleoanthropology, scientists look at the space between the lower canine teeth and first premolars where the upper canine fits as a common characteristic of apes, who have larger canines than humans.

Divergent evolution: A kind of evolutionary change that results in increasing morphological difference between initially more similar lineages.

Ecological species concept: A concept of species, according to which a species is a set of organisms adapted to a particular, discrete set of resources (or "niche") in the environment.

Endocast: An endocast is a cast that shows the brain's impression on the inside of the skull. Endocasts can be artificially made by spreading a mold into an empty skull to represent the skull's brain. The artificial brain is then removed to show the brain's impression, or lines and ridges on its outside surface, that formed against the skull's inside. Endocasts can also form naturally by sediments filling up the inside of an empty skull and fossilizing.

Environmental variability hypothesis: The hypothesis that adaptation to a variable environment, rather than a static environment or directional change, has characterized human evolution

Epigenetics: The study of heritable changes in gene expression that occur without a change in DNA sequence.

Evolution: Descent with modification. The process that results in heritable changes in a population spread over many generations (change in allele frequencies over time). Biological evolution refers to populations and not to individuals and that the changes must be passed on to the next generations. Genes mutate, individuals are selected, and populations evolve.

Evolutionary Developmental Biology (Evo-Devo): The branch of evolutionary biology studying the relationships between changes in developmental pathways due to mutations in regulatory parts of genes and evolutionary changes (macroevolution). The emphasis is on the changes in expression patterns of the genes involved in developmental pathways rather than structural changes in genes.

Extinction: The disappearance of a species or a population.

Fauna: animals that are characteristic of a certain age, locality, or formation.

Fitness: Lifetime reproductive success of an individual (i.e., the total number of offspring who themselves survive to reproduce). It can be seen as the extent to which an individual successfully passes on its genes to the next generation. It has two components: survival (viability) and reproductive success (fecundity). Variation in fitness is the major driving force in biological evolution. The success of an individual (or allele or genotype in a population) in surviving and reproducing, measured by that individual's (or allele's or genotype's) genetic contribution to the next generation and subsequent generations.

Flake: A sharp piece of stone intentionally removed from a core

Flora: Plant life; often used to distinguish from animal life ("fauna").

Foramen magnum: The foramen magnum is the hole at the base of the skull through which the spinal cord enters into the skull and connects to the brain. This hole is one of the key ways scientists can tell the difference between a bipedal human skull and the skull of a quadrupedal great ape. In humans, the foramen magnum is underneath the skull, allowing humans to hold their head upright and look forward. In a great ape, where the ape’s head rests in front of the neck instead of on top, the foramen magnum is positioned at the rear of the head so its eyes face forward, and not down, as it moves.

Fossil: A preserved trace of a once-living organism. A fossilized bone occurs when the living (organic) cells and tissue have become replaced with external minerals while buried in the ground. Virtually all early human fossils are bones in which this process of mineral replacement has taken place. Footsteps can be fossilized.

Fossil record: the history of life on Earth through geological time, as preserved through fossil remains in sedimentary rock (sometimes referred to poetically in older books as the record of the rocks). Also the fossil history of any particular group.

Fossilization: All the processes that involve the burial of a plant or animal in sediment and the eventual preservation of all, part, or a trace of it

Founder effect (Sewall Wright effect): A type of genetic drift in which allele frequencies are altered in a small population, which is a nonrandom sample of a larger (main) population.

Gene flow: The movement of genes within a population or between two populations following genetic admixture. Gene flow creates new combinations of genes or alleles in individuals that can be tested against the environment. This way it is one of the sources of variation in the process of natural selection.

Genetic drift: Evolutionary change over generations due to random events in small populations (not to be mixed with sampling error due to a small sample size). It operates unless overcome by strong selective forces. Changes in the frequencies of alleles in a population that occur by chance, rather than because of natural selection.

Genetic fitness: Classic genetic fitness is the average direct reproductive success of an individual possessing a specific genotype in comparison to others in the population. Inclusive fitness is described as the classic fitness plus the probability that an individual's genotype may be passed on through relatives.

Genotype: The set of two genes possessed by an individual at a given locus. More generally, the genetic profile of an individual.

Genus: is a taxonomic rank used in the biological classification of living and fossil organisms in biology. In the hierarchy of biological classification, genus comes above species and below family. In binomial nomenclature, the genus name forms the first part of the binomial species name for each species within the genus. i.e. Homo sapiens – sapiens is a genus in the species Homo

Geological timescale: The period between the origin of earth (4,500 Mya) and the beginning of the Cambrian period (540 Mya) is called the Precambrian Eon. The last 540 million years (Phanerozoic Eon) are divided into three eras: Palaeozoic (540-245 Mya); Mesozoic (245-65 Mya); Cainozoic. The geological periods (included in an era, longer than an epoch) are as follows: Vendian (immediately before the Cambrian; 610-540 Mya); Cambrian (540-510 Mya); Ordovician; Silurian; Devonian; Carboniferous; Permian; Triassic / Jurassic / Cretaceous (altogether the Mesozoic Era); Tertiary (65-1.64 Mya) and Quaternary. An epoch is a subdivision of a period

Glaciation: The formation of large sheets of ice across land. Glaciation of the continents marks the beginning of ice ages, when the makeup of Earth and organisms on it changes dramatically.

Great Apes: Chimpanzees (including bonobos), gorillas, and orangutans. 

Hammerstone: Cobble used to strike flakes from a stone core

Holocene: An epoch of the Quaternary period, spanning the time from the end of the Pleistocene (10,000 years ago) to the present. The most recent period of geologic history, which extends from 10,000 years ago to the present.

Holotype: Similar to a ‘type specimen,’ for fossil species, the ‘holotype’ of a species is the fossil specimen used when the species is formally described.

Hominid: Refers to the evolutionary group of great apes, including living Asian great apes (orangutans), living African great apes (chimpanzees, bonobos, and gorillas), and humans. This word comes from Hominidae, a formal biological term that is more specific than Hominoidea (= all apes – the great apes and the lesser apes, which include gibbons and siamangs). Some researchers still use the word hominid to refer to the human evolutionary group alone (what we call hominin). This usage goes back to the tradition when humans (hominids) were considered completely divided from all great apes (pongids).

Hominin: Refers to the human evolutionary group of species, including fossil and modern. This word comes from Hominini, a formal biological term in between the level of genus (e.g., Homo, Australopithecus, etc.) and the level of family (Hominidae).

Homologous structures: The structures shared by a set of related species because they have been inherited, with or without modification, from their common ancestor. For example, the bones that support a bat's wing are similar to those of a human arm.

Homology: A similarity due to inheritance from a common ancestor.A character shared by a set of species and present in their common ancestor. Compare with analogy.

Homo erectus: A species of hominid that lived between 1.8 mya and 300,000 years ago; the first Homo species to migrate beyond Africa.

Homo habilis: A species of hominid that lived between 1.9 and 1.8 mya, the first species in genus Homo, and the first hominid associated with clear evidence of tool manufacture and use.

Homo neanderthalensis: A species of hominid that lived between 150,000 and 30,000 years ago in Europe and Western Asia, originally thought to be a geographic variant of Homo sapiens but now generally accepted to be a distinct species.

Homo sapiens: Modern humans, which evolved to their present form about 100,000 years ago.

Homoplasy: a character state that is shared by two or more taxa due to some cause other than common ancestry. The two main types of homoplasy are convergence (evolution of the "same" character in at least two distinct lineages) and reversion (the return to an ancestral character state)

Humerofemoral index: The humerofemoral index is measure comparing arm length to leg length. The index is defined by the arm length divided by the leg length times 100. Modern apes and chimpanzees have arms and legs that are almost the same size in length, giving them a humerfoemoral index of about 100. Humans, with shorter arms than legs, have a humerofemoral index of about 70.

Hypothesis: A proposed, testable scientific explanation for a particular set of phenomena

Inheritance of acquired characters: Historically influential but factually erroneous theory that an individual inherits characters that its parents acquired during their lifetimes. Lamarckian inheritance.

In situ: The words 'in situ' are Latin meaning 'in the place.' In prehistoric studies, in situ refers to an artifact or fossil that has not been taken out of the original location where it was found. In situ materials are undisturbed, which allows archaeologists to date them

and/or give them better context by looking at what artifacts or sediments are found nearby.

Intelligent design: The non-scientific argument that complex biological structures have been designed by an unidentified supernatural or extraterrestrial intelligence.

Land bridge: A connection between two land masses, especially continents (e.g., the Bering land bridge linking Alaska and Siberia across the Bering Strait) that allows migration of plants and animals from one land mass to the other.

Linnaean classification: A hierarchical method of naming classificatory groups, invented by the 18th-century Swedish naturalist Carl von Linné, or Linnaeus. Each individual is assigned to a species, genus, family, order, class, phylum, and kingdom, and some intermediate classificatory levels. Species are referred to by a Linnaean binomial of its genus and species, such as Homo sapiens.

Lithic: Consisting of stone or rock

Lyell's notion of gradual change: Also called uniformitarianism, Lyell's notion was that Earth has been shaped by the same forces and processes that operate today, acting continuously over very long periods of time. For example, the ongoing erosion caused by flowing water in a river could, given enough time, carve out the Grand Canyon.

Macroevolution: Evolution that occurs at the higher levels of taxa (genera, families etc). A vague term generally used to refer to evolution on a grand scale, or over long periods of time. There is no precise scientific definition for this term, but it is often used to refer to the emergence or modification of taxa at or above the genus level. The origin or adaptive radiation of a higher taxon, such as vertebrates, could be called a macroevolutionary event.

Mandible: Lower jaw

Megadont: Megadont ('megadont' meaning 'having large teeth') species have huge, broad cheek teeth with thick enamel while their incisor teeth stay small. The emphasis for megadont species is on the rear teeth, which are designed to support the stresses of heavy chewing. Combined with the morphology of the other parts of the skull -- large zygomatic arches to allow the passage of large chewing muscles and a large sagittal crest to provide a large area to anchor these muscles to the skull -- megadont early humans showed adaptations to chewing tough, fibrous foods.

Meme: The word coined by Richard Dawkins for a unit of culture, such as an idea, skill, story, or custom, passed from one person to another by imitation or teaching. Some theorists argue that memes are the cultural equivalent of genes, and reproduce, mutate, are selected, and evolve in a similar way.

Mendelian inheritance: The mode of inheritance of all diploid species, and therefore of

nearly all multicellular organisms. Inheritance is controlled by genes, which are passed on to the offspring in the same form as they were inherited from the previous generation. At each locus an individual has two genes -- one inherited from its father and the other from its mother. The two genes are represented in equal proportions in its gametes

Microevolution: Evolution of species over relatively short times like several generations. Evolutionary changes on the small scale, such as changes in gene frequencies within a population.

Miocene: Geologic time period ranging from about 23 million to 5.3 million years ago

Missing link: An absent member needed to complete an evolutionary lineage. Use transitional form instead

Modern synthesis: The synthesis of natural selection and Mendelian inheritance. Also called neo-Darwinism.

Molecular (Protein) clock hypothesis: The idea that amino acid replacements occur at a constant rate in a given protein family (ribosomal proteins, cytochromes, etc) and the degree of divergence between two species can be used to estimate the time elapsed since their divergence. The theory that molecules evolve at an approximately constant rate. The difference between the form of a molecule in two species is then proportional to the time since the species diverged from a common ancestor, and molecules become of great value in the inference of phylogeny.

Monophyletic: In cladistics, a monophyletic group is a taxon (group of organisms) which forms a clade, meaning that it consists of an ancestral species and all its descendants. Monophyletic groups are typically characterized by shared derived characteristics (synapomorphies). A monophyletic taxon is also called a clade

Morphology: study of form, shape and structure of animals and plants and their fossil remains.

Most recent common ancestor: (MRCA, also last common ancestor LCA, or concestor) of any set of organisms is the most recent individual from which all organisms in a group are directly descended

Mutation: Any heritable change (not only point mutation) brought about by an alteration in the genetic material. Includes gene conversion, deletion, duplication, insertion and so forth. A change in genetic material that results from an error in replication of DNA. Mutations can be beneficial, harmful, or neutral.

Mya: Million years ago. Also Ma.

Natural selection: Natural selection is the differential survival and reproduction of individuals due to differences in phenotype. Darwin's definition, 1859: "As many more individuals of each species are born than can possibly survive; and as, consequently, there is a frequent recurrent struggle for existence, it follows that any being, if it varies however slightly in any manner profitable to itself, under the complex and sometimes

varying conditions of life, will have a better chance of surviving, and thus be naturally selected." The differential survival and reproduction of classes of organisms that differ from one another in on or more usually heritable characteristics. Through this process, the forms of organisms in a population that are best adapted to their local environment increase in frequency relative to less well-adapted forms over a number of generations. This difference in survival and reproduction is not due to chance.

Neo-Darwinism: (1) Darwin's theory of natural selection plus Mendelian inheritance. (2) The larger body of evolutionary thought that was inspired by the unification of natural selection and Mendelism. A synonym of the modern synthesis.

Neolithic: Last part of the Stone Age, before the origin of metal tools

Neoteny: Retention of juvenile features in sexually mature adult animals. Neoteny frequently correlates with recent evolution of the species (like Homo sapiens).

Niche: The ecological role of a species; the set of resources it consumes and habitats it occupies.

Orthogenesis: The erroneous idea that species tend to evolve in a fixed direction because of some inherent force driving them to do so.

Paleoanthropology: the study of fossil hominids, especially human ancestors.

Paleocene: Earliest epoch of the Tertiary period, spanning the time between 65 and 55.5 million years ago.

Paleomagnetism: Study of the Earth's past magnetism as it is recorded in the rocks.

Paleontology: The study of fossils.

Parallel evolution: Evolution of roughly similar changes in two or more closely related lineages.

Parapatric speciation: Speciation that occurs as a result of two populations diverging in adjacent geographical areas.

Peripheral isolate speciation: A form of allopatric speciation in which the new species is formed from a small population isolated at the edge of the ancestral population's geographic range. Also called peripatric speciation.

Phenotype: composite of an organism's observable characteristics or traits. The physical or functional characteristics of an organism, produced by the interaction of genotype and environment during growth and development.

Phyletic gradualism: A model of evolutionary mode characterized by slow and gradual modifications of biological structures leading to speciation. This is the opposite of punctuated equilibrium

Phylogeny: the study of ancestral relations among species; (also known as a phylogenetic tree) – a diagrammatic hypothesis about the history of the evolutionary relationships of a group of organisms

Platyrrhini: New world monkeys found in South America with widely spaced nostrils. They last had a common ancestor with the old world monkeys (Catarrhini) about 55 million years ago.

Plesiomorphy: the ancestral trait state, usually in reference to a derived trait state. The scientific term for an ancestral trait is called a plesiomorphy, which means it is a character that has been inherited from a common ancestor and has remained unchanged. A plesiomorphy for the genus Homo is an opposable thumb. All members of Homo have one, as do all other hominins and primates, suggesting that the groups inherited this trait from a common ancestor. Whether a trait is ancestral or derived changes depending on the groups you are comparing. A small canine tooth is a synapomorphy for hominins, but it'd be considered a plesiomorphy for the genus Homo when compared to other hominin groups.

Pleistocene: Geological time period ranging from about 1.8 million years ago - or, for some researchers, 2.6 million years ago - to about 10,000 years ago

Pliocene: Final epoch of the Tertiary period, spanning the time between 5.3 and 1.8 million years ago

Polyphyletic: (Greek for "of many races") group is characterized by one or more homoplasies: phenotypes which have converged or reverted so as to appear to be the same but which have not been inherited from common ancestor. A set of species descended from more than one common ancestor. The ultimate common ancestor of all species in the group is not a member of the polyphyletic group, usually because the common ancestor lacks the characteristics of the group.

Population: A group of organisms, usually a group of sexual organisms that interbreed and share a gene pool.

Post-cranial: A bone or bone(s) from any part(s) of the skeleton that does not include the skull (cranium and mandible).

Primates: One of the Mammalian Orders which includes Lemurs (suborder Prosimii), old world and new world Monkeys, Apes and Humans. The suborder Anthropoidea covers all Primates except Prosimii. Prosimians and Anthropoids diverged from each other 65 Mya; Apes and Old World Monkeys 35 Mya. The separation of the two groups of Anthropoids (Platyrrhini and Catarrhini) occurred about 55 Mya.

Prognathic: A fossil skull is called prognathic when the lower face, and sometimes jaw, protrudes forward.

Punctuated equilibrium: Put forward by Niles Eldredge and Stephen Jay Gould in 1972 as a counter theory to Darwin's gradualism in speciation (see phyletic gradualism). It suggests that new species may have arisen rapidly over a few thousand years and then remained unchanged (stasis) for many millions of years. Punctuated equilibrium postulates that change occurred in only a small part of the population (rather than the whole population is evolving gradually). The most plausible explanation for a

sudden and drastic change would be mutations in regulatory sequences that affect a whole operon (see Gould SJ & N Eldredge. Punctuated equilibria: the tempo and mode of evolution reconsidered. Paleobiology 1977;3:115-51)

Race: Described in population genetics as a geographic subdivision of a species distinguished from others by the allele frequencies of a number of genes. A beautiful discussion that there are no genetically defined races within Homo sapiens can be found in Cavalli-Sforza's book  Genes, Peoples, and Languages  (2000).

Radiometric dating: A dating technique that uses the decay rate of radioactive isotopes to estimate the age of an object.

Reproductive isolation: Two populations or individuals of opposite sex are considered reproductively isolated from one another if they cannot together produce fertile offspring. See prezygotic isolation and postzygotic isolation.

Sagittal crest: A sagittal crest is the bony ridge on the top of the skull where the jaw muscles of some early humans were anchored allowing powerful chewing (a modern human’s jaw muscles are anchored beside their ears). This ridge runs lengthwise down the middle of the top of the skull.

Science: A way of knowing about the natural world based on observations and experiments that can be confirmed or disproved by other scientists using accepted scientific techniques. Requires falsifiability.

Sedimentary rocks: Rocks composed of sediments, usually with a layered appearance. The sediments are composed of particles that come mostly from the weathering of pre-existing rocks, but often include material of organic origin; they are then transported and deposited by wind, water, or glacial ice. Sedimentary rocks are deposited mainly under water, usually in approximately horizontal layers (beds). Often site of fossils.

Selective pressures: Environmental forces such as scarcity of food or extreme temperatures that result in the survival of only certain organisms with characteristics that provide resistance.

Sexual dimorphism: Sexual dimorphism is size or shape difference between males and females of the same species. Similarly-sized males and females within a species show less sexual dimorphism, and this phenomenon is generally attributed to monogamous bonding between males and females (like in many modern humans). Greater sexual dimorphism generally means a species is more polygamous.

Sexual selection: Natural selection operating on factors that contribute to an organism's mating success. Described by Darwin as natural selection in relation to sex.

Speciation: It is now almost universally agreed that the prevailing process of speciation is geographical (allopatric) speciation. (There are also parapatric and sympatric

speciation concepts.) According to biological species concept, however, species are defined as aggregation of populations that are reproductively isolated from one another.

Species: the basic unit of biological classification and a taxonomic rank. A species is often defined as the largest group of organisms in which two individuals can produce fertile offspring, typically by sexual reproduction. All members of a population or set of populations that actually or potentially interbreed over time

Stratigraphic layer: A stratigraphic layer is a geological layer of rock and/or soil. The law of superposition says that if you were to dig a hole, the layers of earth at the bottom of the hole would be older than the layers of earth at the top. By recognizing these stratigraphic layers, scientists can date fossil or archaeological finds, or other features, and compare their ages to one another.

Stratigraphy: Branch of geology concerned with the formation, composition, ordering in time, and arrangement in space of sedimentary rocks.

Sympatric speciation: Speciation via populations with overlapping geographic ranges.

Synapomorphy: a characteristic present in an ancestral species and shared exclusively (in more or less modified form) by its evolutionary descendants. Synapomorphy is a shared derived character or trait that distinguishes a clade from other organisms. Researchers must decide which character states are "ancestral" (plesiomorphies) and which are derived (synapomorphies), because only synapomorphic character states provide evidence of grouping. The term synapomorphy refers to an apomorphy shared by a group. A synapomorphy for hominins, for example, is greatly reduced canine teeth. Male chimpanzees and other close non-hominin relatives have huge canine teeth, probably used in threat displays. Hominins do not have this character, suggesting that the trait changed sometime after the hominin lineage and chimpanzee lineage split.

Systematics: A near synonym of taxonomy

Taxonomy: The theory and practice of biological classification

Taxon: a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Any group of organisms to which any rank of taxonomic name (classification) is applied

Taxonomic hierarchy: All taxa are classified within the following groups (starting from the most inclusive): kingdom, ('division' in plants), phylum, class, order, family, genus, species, subspecies (race).

Teleology: Teleology, from the Greek word telos (purpose), asserts that there is an element of purpose or design behind the workings of nature. Attributing any purposeful direction to evolutionary change would be called teleological. Not true.

Theory: A well-substantiated explanation of some aspect of the natural world that typically incorporates many confirmed observations, laws, and successfully verified hypotheses.

Transitional fossil: A fossil or group of fossils representing a series of similar species, genera, or families, that link an older group of organisms to a younger group. Often, transitional fossils combine some traits of older, ancestral species with traits of more recent species (for instance, a series of transitional fossils documents the evolution of fully aquatic whales from terrestrial ancestors).

Type specimen: In paleontological studies, a species' type specimen is a specific fossil for which the species was first named.

Young Earth creationism: The belief that the universe came into being only a few thousand years ago. Most young Earth creationists interpret the Bible literally, including not just the special, separate creation of human beings and all other species, but the historicity of Noah's flood

Zygomatic arch: The zygomatic arch is the bone forming your cheek that rests above the indention you feel in front of your ear, which allows the passage of your chewing muscles through from your jaw to where they connect to your skull. Robust species had larger, or flaring, zygomatic arches, allowing space for more powerful chewing muscles.

Glossary of human bones

Skull:

Mandible: lower jaw or jawbone (from Latin mandibula, "jawbone") is the largest, strongest and lowest bone in the face. It forms the lower jaw and holds the lower teeth in place. The mandible sits beneath the maxilla.

Maxilla: upper jawbone formed from the fusion of two bones. The upper jaw includes the frontal portion of the palate of the mouth

Arm:

Humerus: a long bone in the arm or forelimb that runs from the shoulder to the elbow; upper arm bone

Radius: one of the two large bones of the forearm

Ulna: a long bone found in the forearm that stretches from the elbow to the smallest finger, and when in anatomical position, is found on the medial side of the forearm. It runs parallel to the radius, the other long bone in the forearm, and is the larger and longer of the two.

Legs:

Femur: the thigh bone, is the most proximal (closest to the hip joint) bone of the leg. The head of the femur articulates with the acetabulum in the pelvic bone forming the hip joint, while the distal part of the femur articulates with the tibia and kneecap forming the knee joint. The longest and strongest bone.

Fibula: the calf bone is a leg bone located on the lateral side of the tibia, with which it is connected above and below. It is the smaller of the two bones

Tibia: the shinbone, is the larger and stronger of the two bones in the leg below the knee

Hand and fingers:

Carpal bones: the eight small bones that make up the wrist (or carpus) that connects the hand to the forearm

Metacarpals: bones that form the intermediate part of the skeletal hand located between the phalanges of the fingers and the carpal bones of the wrist which forms the connection to the forearm.

Phalanges: digital bones in the hands and feet of most vertebrates. In primates, the thumbs and big toes have two phalanges while the other digits have three phalanges.

Toes:

Metatarsals: group of five long bones in the foot, located between the tarsal bones of the hind- and mid-foot and the phalanges of the toes

Condyle: is the round prominence at the end of a bone, most often part of a joint – an articulation with another bone.

Foramen: any opening, particularly referring to those in bone.

Joint, or articulation: the region where adjacent bones contact each other, for example the elbow

Ramus: (Latin: branch) refers to an extension of bone, such as the ramus of the mandible in the jaw

Scapula: a.k.a. shoulder blade, is the bone that connects the humerus (upper arm bone) with the clavicle (collar bone).

Sinus: a bony cavity, usually within the skull.

Suture: an articulation between cranial bones.

Vertebra: bones of the spine

Teeth:

20 primary (deciduous, "baby" or "milk") teeth and 32 permanent (adult) teeth

Among permanent teeth, 16 are found in the maxilla and 16 in the mandible, for a total of 32. The dental formula is 2.1.2.3/2.1.2.3

The maxillary teeth are the central incisor (I2), lateral incisor (I2), canine ©, first premolar (P3), second premolar (P4), first molar (M1), second molar (M2), and third molar (M3). The mandibular teeth are the central incisor (I1), lateral incisor (I2), canine (C), first premolar (P3), second premolar (P4), first molar (M1), second molar (M2), and third molar (M3). Third molars are commonly called "wisdom teeth" and may never erupt into the mouth or form at all. Eruption = anatomically modern humans have the sequence M1 I1 I2 C P3 P4 M2 M3.

Incisors are generally spatulate with a single root while canines are also single rooted but are single cusped and conical. Premolars are bicuspid while molars are multi-cuspid. The upper molars have three roots while the lower molars have two roots.

General patterns of dental morphological evolution throughout human evolution include a reduction in facial prognathism, the presence of a Y5 cusp pattern, the formation of a parabolic palate and the loss of the diastema.