Allele: A nonidentical DNA sequence found in the same gene location on a homologous chromosome, or gene copy, that codes for the same trait but produces a different phenotype.
Artificial selection: The identification by humans of desirable traits in plants and animals, and the subsequent steps taken to enhance and perpetuate those traits in future generations.
Binomial nomenclature: A system of classification in which a species of animal or plant receives a name consisting of two terms: the first identifies the genus to which it belongs, and the second identifies the species.
Carrying capacity: The number of living organisms, including animals, crops, and humans, that a geographic area can support without environmental degradation.
Catastrophism: The theory that the Earth’s geology has largely been shaped by sudden, short-lived, violent events, possibly worldwide in scope. Compare to uniformitarianism.
Comparative anatomy: Georges-Louis Leclerc’s technique of comparing similar anatomical structures across different species.
Creationism: The belief that the universe and all living organisms originate from specific acts of divine creation, as in the Biblical account, rather than by natural processes such as evolution.
Empiricism: The idea that all learning and knowledge derives from experience and observation. It became prominent in the 17th and 18th centuries in western Europe due to the rise of experimental science.
Evolution: In a biological sense, this term refers to cumulative inherited change in a population of organisms through time. More specifically, evolution is defined as a change in allele (gene) frequencies from one generation to the next among members of an interbreeding population.
Extant: Still in existence; surviving.
Extinct: Said of a species, family, or other group of animals or plants that has no living members; no longer in existence.
Fixity of Species: The idea that a species, once created, remains unchanged over time.
Gene: A sequence of DNA that provides coding information for the construction of proteins.
Genetic drift: Random changes in allele frequencies within a population from one generation to the next.
Gene flow: The introduction of new genetic material into a population through interbreeding between two distinct populations.
Gene pool: The entire collection of genetic material in a breeding community that can be passed from one generation to the next.
Genotype: The genotype of an organism is its complete set of genetic material—its unique sequence of DNA. Genotype also refers to the alleles or variants an individual carries in a particular gene or genetic location.
Hybrid: Offspring of parents that differ in genetically determined traits.
Intelligent design: A pseudoscientific set of beliefs based on the notion that life on earth is so complex that it cannot be explained by the scientific theory of evolution and therefore must have been designed by a supernatural entity.
Macroevolution: Large and often-complex changes in biological populations, such as species formation.
Microevolution: Changes in the frequency of a gene or allele in an interbreeding population.
Modern synthesis: The mid–20th century merging of Mendelian genetics with Darwinian evolution that resulted in a unified theory of evolution.
Natural selection: The natural process by which the survival and reproductive success of individuals or groups within an interbreeding population that are best adjusted to their environment leads to the perpetuation of genetic qualities best suited to that particular environment at that point in time.
Phenotype: The detectable or visible expression of an organism’s genotype.
Scientific method: A method of procedure that has characterized natural science since the 17th century, consisting of systematic observation, measurement, experimentation, and the formulation, testing, and modification of hypotheses.
Speciation: The process by which new genetically distinct species evolve from the main population, usually through geographic isolation or other barriers to gene flow.
Species: A group of living organisms consisting of similar individuals capable of exchanging genes or interbreeding. The species is the principal natural taxonomic unit, ranking below a genus and denoted by a Latin binomial (e.g., Homo sapiens).
Uniformitarianism: The theory that changes in the earth’s crust during geologic history have resulted from the action of continuous and uniform processes—such as wind, precipitation, evaporation, condensation, erosion, and volcanic action—that continue to act in the present. Compare to catastrophism.