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Definition
| Evolutionary change below the spcecies level; change in the allele frequencies in a population over generations. |
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| Differences among individuals int he composition of their genes or other DNA segments. |
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| The percentage, on average, of a population's loci that are heterozygous in members of the population. |
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| Differences between the gene pools of geographically separate populations or population subgroups. |
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| A graded change in a character along a geographic axis. |
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| A group of individuals of the same species that live in the same area and interbreed, producing fertile offspring. |
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| The aggregate of all copies of every type of allele at all loci in every individual in a population. The term is used in a more restricted sense as the aggregate of alleles for just one or a few loci in a population. |
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| The principle that frequencies of alleles and genotypes in a population remain constant from generation to generation, provided that only Mendelian segregation and recombination of alleles are at work. |
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| A process in which chance events cause unpredictable fluctuations in allele frequencies from one generation to the next. Effects of genetic drift are most pronounced in small populations. |
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| Genetic drift that occurs when a few individuals become isolated from a larger population and form a new population whose gene pool composition is not reflective of that of the original population. |
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| Genetic drift that occurs when the size of a population is reduced, as by a natural disaster or human actions. Typically, the surviving population is no longer genetically representative of the original population. |
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Definition
| The transfer of alleles from one population to another, resulting from the movement of fertile individuals or their gametes. |
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| The contribution an individual makes to the gene pool of the next generation, relative to the contributions of other individuals in the population. |
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Definition
| Natural selection in which individuals at one end of the phenotypic range survive or reproduce more successfully than do other individuals. |
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| Natural selection in which individuals on both extremes of a phenotypic range survive or reproduce more successfully than do individuals with intermediate phenotypes. |
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| Natural selection in which intermediate phenotypes survive or reproduce more successfully than do extreme phenotypes. |
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| A form of selection in which individuals with certain inherited characteristics are more likely than other individuals to obtain mates. |
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| Differences between the secondary sex characteristics of males and females. |
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| Selection in which there is direct competition among individuals of one sex for mates of the opposite sex. |
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| Selection whereby individuals of one sex (usually females) are choosy in selecting their mates from individuals of the other sex; also called mate choice. |
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| Genetic variation that does not provide a selective advantage or disadvantage. |
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Definition
| Natural selection that maintains two or more phenotypic forms in a population. |
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Definition
| Greater reproductive success of heterozygous individuals compared with homozygotes; tends to preserve variation in a gene pool. |
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| frequency-dependent selection |
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Definition
| Selection in which the fitness of a phenotype depends on how common the phenotype is in a population. |
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Definition
| An evolutionary process in which one species splits into two or more species. |
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Definition
| Evolutionary change below the species level; change in the allele frequencies in a population over generations. |
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Definition
| Evolutionary change above the species level. Examples of macroevolutionary change include the origin of a new group of organisms through a series of speciation events and the impact of mass extinctions on the diversity of life and its subsequent recovery. |
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| biological species concept |
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Definition
| Definition of a species as a group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring, but do not produce viable, fertile offspring with members of other such groups. |
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Definition
| A population or group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring, but do not produce viable, fertile offspring with members of other such groups. |
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Definition
| The existence of biological factors (barriers) that impede members of two species from producing viable, fertile offspring. |
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Definition
| Offspring that results from the mating of individuals from two different species or from two true-breeding varieties of the same species. |
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Definition
| A reproductive barrier that impedes mating between species or hinders fertilization if interspecific mating is attempted. |
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Definition
| A reproductive barrier that prevents hybrid zygotes produced by two different species from developing into viable, fertile adults. |
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| morphological species concept |
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Definition
| A definition of species in terms of measurable anatomical criteria. |
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| ecological species concept |
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Definition
| A definition of species in terms of ecological niche, the sum of how members of the species interact with the nonliving and living parts of their environment. |
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| phylogentic species concept |
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Definition
| A definition of species as the smallest group of individuals that share a common ancestor, forming one branch on the tree of life. |
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Definition
| The formation of new species in a population that are geographically isolated from one another. |
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| The formation of new species in populations that live in the same geographic area. |
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| A chromosomal alteration in which the organism possesses more than two complete chromosome sets. It is the result of an accident of cell division. |
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Definition
| An individual that has more than two chromosome sets that are all derived from a single species. |
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Definition
| A fertile indivdual that has more than two chromosome sets as a result of two different species interbreeding and combining their chromosomes. |
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| A geographic region in which members of different species meet and mate, producing at least some offspring of mixed ancestry. |
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Definition
| In evolutionary biology, a process in which natural selection strengthens prezygotic barriers to reproduction, thus reducing the chances of hybrid formation. Such a process is likely to occur only if hybrid offspring are less fit than members of the parent species. |
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| In the fossil record, long periods of apparent stasis, in which a species undergoes little or no morphological change, interrupted by relatively brief periods of sudden change. |
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Definition
| Evolutionary change above the species level. Examples of macroevolutionary change include the origin of a new group of organisms through a series of speciation events and the impact of mass extinctions on the diversity of life and its subsequent recovery. |
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Definition
| An abiotic precursor of a living cell that had a membrane-like structure and that maintained an internal chemistry different from that of its surroundings. |
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Definition
| An RNA molecule that functions as an enzyme, such as an intron that catalyzes its own removal during RNA splicing. |
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Definition
| An isotope (an atomic form of a chemical element) that is unstable; the nucleus decays spontaneously, giving off detectable particles and energy. |
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Definition
| The amount of time it takes for 50% of a sample of a radioactive isotope to decay. |
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Definition
| The division of Earth's history into time periods, grouped into three eons--Archaean, Proterozoic, and Phanerozoic--and further subdivided into eras, periods, and epochs. |
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| The theory that mitochondira and plastids, including chloroplasts, originated as prokaryotic cells engulfed by an ancestra eukaryotic cell. The engulfed cell and its host cell then evolved into a single organism. |
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Definition
| A hypothesis for the origin of eukaryotes consisting of a sequence of endosymbiotic events in which mitochondria, chloroplasts, and perhaps other cellular structures were derived from small prokaryotes that had been engulfed by larger cells. |
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Definition
| A relativeily brief time in geologic history when many present-day phyla of animals first appeared in the fossil record. This burst of evolutionary change occurred about 535-525 million years ago and saw the emergence of the first large, hard-bodied animals. |
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Definition
| The theory that the continents are part of great plates of Earth's crust that float on the hot, underlying portion of the mantle. Movements in the mantle cause the continents to move slowly over time. |
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Definition
| The supercontinet that formed neaer the end of the Paleozoic era, when plate movements brought all the landmasses of Earth together. |
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Definition
| The elimination of a large number of species throughout Earth, the result of global environmental changes. |
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| Period of evolutionary change in which groups of organisms form many new species whose adapatations allow them to fill different ecological roles in their communities. |
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| Evolutionary change in the timing or rate of an organism's development. |
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Definition
| The retention in an adult organism of the juvenile features of its evolutionary ancestors. |
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Definition
| Any of the master regulatory genes that control placement and spatial organization of body parts in animals, plants, and fungi by controlling the developmental fate of groups of cells. |
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Definition
| The evolutionary history of a species or group of related species. |
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Definition
| A scientific discipline concerned with naming and classifying the diverse forms of life. |
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Definition
| The two-part, latinized format for naming a species, consisting of the genus and specific ephitet; a binomen. |
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Definition
| A taxonomic category above the species level, designated by the first word of a species' two-part scientific name. |
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Definition
| In Linnaeaen classification, the taxonomic category above genus. |
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Definition
| In Linnaean classification, the taxonomic category above family. |
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Definition
| In Linnaean classification, the taxonomic category above family. |
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| In Linnaean classification, the taxonomic category above class. |
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Definition
| A taxonomic category, the second broadest after domain. |
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Definition
| A taxonomic category above the kingdom level; the three domains are Archaea, Bacteria, and Eukarya. |
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Definition
| A named taxonomic unit at any given level of classification. |
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Definition
| A branching diagram that represents a hypothesis about the evolutionary history of a group of organisms. |
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Definition
| Proposed system of classification of organisms based on evolutionary relationships: Only groups that include a common ancestor and all of its descendants are named. |
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Definition
| The representation on a phylogenetic tree of the divergence of two or more taxa froma common ancestor. A branch point is usually shown as a dichotomy in which a branch representing the ancestral lineage splits (at the branch point) into two branches, one for each of the two descendant lineages. |
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Definition
| Groups of organisms that share an immediate common ancestor and hence are each other's closest relatives. |
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Definition
| In a specified group of organisms, a taxon whose evolutionary lineage diverged early in the history of the group. |
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Definition
| In a phylogenetic tree, a branch point from which more than two descendant taxa emerge. A polytomy indicates that the evolutionary relationships between the descendant taxa are not yet clear. |
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Definition
| Similarity between two species that is due to convergent evolution rather than to descent from a common ancestor with the same trait. |
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Definition
| An approach to systematics in which organisms are placed into groups called clades based primarily on common descent. |
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Definition
| a group of species that includes an ancestral species and all of its descendants. |
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Definition
| Pertaining to a group of taxa that consists of a common ancestor and all of its descendants. a monophyletic taxon is equivalent to a clade. |
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Definition
| Pertaining to a group of taxa that consists of a common ancestor and some, but not all, of its descendants. |
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Definition
| Pertaining to a group of taxa derived from two or more different ancestors. |
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Term
| shared ancestral character |
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Definition
| A character, shared by members of a particular clade, that originated in an ancestor that is not a member of that clade. |
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Definition
| An evolutionary novelty that is unique to a particular clade. |
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Definition
| a species or group of species from an evolutionary lineage that is known to have diverged before the lineage that contains the group of species being studied. An outgroup is selected so that its members are closely related to the group of species being studied, but not as closely related as any study-group members are to each other. |
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Definition
| A species or group of species whose evolutionary relationships we seek to determine. |
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Definition
| A principle that states that when considering multiple explanations fro an observation, one should first investigate the simplest explanation that is consistent with the facts. |
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Definition
| As applied to molecular systematics, a principle that states that when considering multiple phylogentic hypotheses, one should take into account the hypothesis that reflects the most likely sequence of evolutionary events, given certain rules about how DNA changes over time. |
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Definition
| Homologous genes that are found in different species because of speciation. |
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Definition
| Homologous genes that are found in the same genome as a result of gene duplication. |
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Definition
| A method for estimating the time required for a given amount of evolutionary change, based on the observation that some regions of genomes evolve at constant rates. |
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Definition
| The hypothesis that much evolutionary change in genes and proteins has no effect on fitness and therefore is not influenced by natural selection. |
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Definition
| The transfer of genes from one genome to another throguh mechanisms such as transposable elements, plasmid exchange, viral activity, and perhaps fusions of different organisms. |
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Definition
| Describing a phylogenetic tree that contains a branch point (often, the farthest to the left) representing the most recent common ancestor of all taxa in the tree. |
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Definition
| A similar (analogous) structure or molecular sequence that has evolved independently in two species. |
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Definition
| A scientific discipline that uses nucleic acids or other molecules to infer evolutionary relationships between different species. |
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