Evolution Unit Vocabulary
Adaptation(s): any inherited characteristic that increases an organism's chance of survival
Adaptive radiation: a process that occurs when a single species has evolved into many diverse species
Allele Frequency The measure of the relative frequency of an allele at a genetic locus in a population; expressed as a proportion or percentage.
Analogous Structure A physical structure, present in multiple species, that is similar in function but different in form and inheritance.
Artificial selection: the breeding of animals for the best characteristics
Behavioral isolation: form of reproductive isolation when there are no sexual cues between representatives of the species; while the two populations are capable of interbreeding they have different behavioral reproductive strategies, which leads to a lack of breeding
Binomial nomenclature: a classification system in which each species is assigned a 2-part scientific name
Brachiopods: small animals with two shells resemble but are not related to clams
Cladogram: diagram that shows the evolutionary relationships among a group of organism
Class: category composed of similar orders
Coevolution: the process by which two species evolve in response to changes in each other, over time
Common descent: the idea that all living things have common ancestors
Convergent evolution: the process by which unrelated organisms resemble each other
Derived characters: characteristics that appear in recent parts of a lineage but not in older members
Descent with modification: each living species has descended, with changes, from other species over time
Directional selection: individuals at one end of a bell curve have greater fitness than individuals in the middle or other end
Disruptive selection: individuals at the extremes of the bell curve have higher fitness than individuals at the center

Ecological isolation: Form of reproductive isolation in which individuals only mate in their specific habitat
Embryology The branch of zoology studying the early development of living things.
Endemic Species A species that is found in its originating location and is generally restricted to that geographic area.
Endosymbiotic theory: theory that proposes that eukaryotic cells formed symbiotic relationships with select prokaryotes, and arose from being prokaryote living communities
Environment The total surroundings of an organism or a group of organisms
Era(s): the divisions in time between the Precambrian and present on the geologic time scale
Evolution: A process in which new species develop from preexisting species (macroevolution); a change in the allele frequencies of a population of organisms from generation to generation
(microevolution).
Evolutionary classification: the strategy of grouping organisms together based on their evolutionary history
Extinct: a term used to describe a species that has died out
Family: the classification of genera that share many characteristics
Fitness: the ability of an individual to survive and reproduce in its specific environment
Fossil record: the collection of fossils that provide evidence about the history of life on earth;
Information about past life, including the structure of organisms, what they ate, what ate them, in what environment they lived, and the order in which they lived.
Fossil(s): preserved remains of ancient organisms
Founder effect: a situation in which allele frequencies change as a result of migration; A decrease in genetic variation caused by the formation of a new population by a small number of individuals from a larger population.
Gametic incompatibility form of reproductive isolation when there is sperm transfer without fertilization occurring
Gene pool: a common group of genes in a population
Genetic drift: A change in the allele frequency of a population as a result of chance events rather than natural selection; individuals with a particular allele may have more descendants by chance, eventually causing this allele to become common

Genetic equilibrium: situation in which allele frequencies remain constant
Genus: a group of closely related species
Geographic isolation: Geographic Isolation Form of reproductive isolation in which two populations are separated physically by geographic barriers such as rivers, mountains, or stretches of water
Geologic time scale: scale used by paleontologists to represent evolutionary time
Gradualism: a slow, steady change in a particular line of descent
Half-life: the length of time required for half of the radioactive atoms in a sample to decay
Hardy Weinberg principle: principle that states that allele frequencies in a population will remain constant unless one or more factors cause those frequencies to change
Homologous structures: structures that have different mature forms but develop from the same embryonic tissues; a physical characteristic in different organisms that is similar because it was inherited from a common ancestor.
Hutton, James: a scientist who proposed the earth was shaped by long natural processes and was millions of years old
Hybrid breakdown form of reproductive isolation where the first generation offspring are viable but future generations are not
Hybrid inviability form of reproductive isolation where the embryo is not viable (does not survive)
Hybrid sterility form of reproductive isolation where the resulting adult is sterile (cannot reproduce)
Index fossils: fossils used to compare the relative age of other fossils
Isolating Mechanisms Features of behaviors, morphology, or genetics which serve to prevent mating or breeding between two different species (e.g., temporal isolation, in which individuals are active at different times of the day, seasons, or mating periods; ecological isolation, in which individuals only mate in their specific habitat; behavioral isolation, when there are no sexual cues between representatives of the species; mechanical isolation, when there is no sperm transfer during an attempted mating; and gametic incompatibility, when there is sperm transfer without fertilization occurring). If mating can take place, there are four factors that prevent hybrid viability: zygotic mortality (fertilization but no zygote), hybrid inviability (embryo is not viable), hybrid sterility (resulting adult is sterile), and hybrid breakdown (first generation is viable but future generations are not).

Kingdom: largest and most inclusive of taxonomic categories
Lamarck, Jean-Baptiste: a scientist who published his hypothesis on the inheritance of acquired traits (this was incorrect but a step forward)
Limiting Factor Chemical or physical factor that limits the existence, growth, abundance, or distribution of an individual organism or a population.
Lyell, Charles: a scientist who explained that current processes have shaped geological features of
Earth over a long period of time
Macroevolution: large-scale evolutionary patterns and processes that occur over long periods of time
Malthus, Thomas Robert: a scientist who proposed that the human population would overrun the food supply
Mass extinction: many types of living things become extinct at the same time
Mechanical isolation form of reproductive isolation when there is no sperm transfer during an attempted mating
Microfossils: microscopic fossils
Migration (Genetics) The permanent movement of genes into or out of a population resulting in a change in allele frequencies.
Miller, Stanley and Urey, Harold: two scientists who experimented about early life, suggested how mixtures of the organic compounds necessary for life would have arisen from simpler compounds on primitive earth
Molecular clock: a model that uses DNA comparisons to estimate the length of time that two species have been evolving independently
Natural selection: A process in nature in which organisms possessing certain inherited traits are better able to survive and reproduce compared to others of their species; traits that aid an organism's survival are passed on to the next generation and eventually to the whole population
Nonnative Species A species normally living outside a distribution range that has been introduced through either deliberate or accidental human activity; also can be known as introduced, invasive, alien, nonindigenous, or exotic.
Order: broad taxonomic category composed of similar features, larger than family
Paleontologist(s): scientists who study fossils
Period(s): subdivisions of eras on the geologic time scale

Phylogeny: evolutionary relationships among organisms
Phylum: many different organisms that share important characteristics, larger than class
Polygenic trait(s): traits controlled by 2 or more alleles
Population A group of individuals of the same species living in a specific geographical area and reproducing.
Population Dynamics The study of short ‐ and long ‐ term changes in the number of individuals for a given population, as affected by birth, death, immigration, and emigration.
Proteinoid microsphere: tiny bubbles formed by large organic molecules under certain condition
Punctuated equilibrium: A proposed explanation in evolutionary biology stating that species are generally stable over long periods of time. Occasionally there are rapid changes that affect some species that can quickly result in a new species
Radioactive dating: the use of half-lives to determine the age of a sample, scientists calculate the age of the sample based on the amount of remaining radioactive isotopes it contains
Random mating: factor of genetic equilibrium; all members of a population have an equal chance to produce offspring
Relative dating: the age of a fossil is determined by its placement with other, dated, fossils
Relative frequency: the number of times that the allele occurs in a gene pool
Reproductive isolation: a process that has occurred when members of two populations cannot interbreed and produce fertile offspring
Selective Breeding The process of breeding organisms that results on offspring with desired genetic traits.
Single-gene trait(s): a trait controlled by a single gene with 2 alleles
Speciation: the formation of new species
Stabilizing selection: individuals near the center of the bell curve have greater fitness than individuals at the extremes of the curve
Struggle for existence: a competition for resources, a central point of Darwin's theory of evolution

Survival of the fittest: individuals better suited to their environment survive and reproduce most successfully
Taxonomy: the discipline of the classification of organisms
Temporal isolation: Form of reproductive isolation in which individuals are active at different times of the day, seasons, or mating periods
Vestigial organ(s): organs that have no useful function in an organism, traces of evolutionary history
Zygotic mortality form of reproductive isolation where there is fertilization but no zygote