adaptation
Any genetically controlled structural, physiological, or behavioral characteristic that helps an organism survive and reproduce under a given set of environmental conditions. It usually results from a beneficial mutation. See biological evolution, differe
adaptive radiation
Process in which numerous new species evolve to fill vacant and new ecological niches in changed environments, usually after a mass extinction. Typically, this takes millions of years.
adaptive trait
See adaptation.
allele
Slightly different molecular form found in a particular gene.
artificial selection
Process by which humans select one or more desirable genetic traits in the population of a plant or animal species and then use selective breeding to produce populations containing many individuals with the desired traits. Compare genetic engineering, nat
background extinction
Normal extinction of various species as a result of changes in local environmental conditions. Compare mass depletion, mass extinction.
biological evolution
Change in the genetic makeup of a population of a species in successive generations. If continued long enough, it can lead to the formation of a new species. Note that populations�not individuals�evolve. See also adaptation, differential reproduction, nat
biopharming
Use of genetically engineered animals to act as biofactories for producing drugs, vaccines, antibodies, hormones, industrial chemicals such as plastics and detergents, and human body organs.
chemical evolution
Formation of the earth and its early crust and atmosphere, evolution of the biological molecules necessary for life, and evolution of systems of chemical reactions needed to produce the first living cells. These processes are believed to have occurred abo
coevolution
Evolution in which two or more species interact and exert selective pressures on each other that can lead each species to undergo various adaptations. See evolution, natural selection.
competition
Two or more individual organisms of a single species (intraspecific competition) or two or more individuals of different species (interspecific competition) attempting to use the same scarce resources in the same ecosystem.
differential reproduction
Phenomenon in which individuals with adaptive genetic traits produce more living offspring than do individuals without such traits. See natural selection.
domesticated species
Wild species tamed or genetically altered by crossbreeding for use by humans for food (cattle, sheep, and food crops), pets (dogs and cats), or enjoyment (animals in zoos and plants in gardens). Compare wild species.
ecological niche
Total way of life or role of a species in an ecosystem. It includes all physical, chemical, and biological conditions a species needs to live and reproduce in an ecosystem. See fundamental niche, realized niche.
evolution
See biological evolution.
extinction
Complete disappearance of a species from the earth. This happens when a species cannot adapt and successfully reproduce under new environmental conditions or when it evolves into one or more new species. Compare speciation. See also endangered species, ma
fossils
Skeletons, bones, shells, body parts, leaves, seeds, or impressions of such items that provide recognizable evidence of organisms that lived long ago.
fundamental niche
The full potential range of the physical, chemical, and biological factors a species can use if there is no competition from other species. See ecological niche. Compare realized niche.
gene flow
Movement of genes between populations, which can lead to changes in the genetic composition of local populations.
gene mutation
See mutation.
gene pool
The sum total of all genes found in the individuals of the population of a particular species.
gene splicing
See genetic engineering.
generalist species
Species with a broad ecological niche. They can live in many different places, eat a variety of foods, and tolerate a wide range of environmental conditions. Examples are flies, cockroaches, mice, rats, and human beings. Compare specialist species.
genetic adaptation
Changes in the genetic makeup of organisms of a species that allow the species to reproduce and gain a competitive advantage under changed environmental conditions. See differential reproduction, evolution, mutation, natural selection.
genetic engineering
Insertion of an alien gene into an organism to give it a beneficial genetic trait. Compare artificial selection, natural selection.
genetically modified organism (GMO)
Organism whose genetic makeup has been modified by genetic engineering.
geographic isolation
Separation of populations of a species for long times into different areas.
habitat
Place or type of place where an organism or population of organisms lives. Compare ecological niche.
macroevolution
Long-term, large-scale evolutionary changes among groups of species. Compare microevolution.
mass depletion
Widespread, often global period during which extinction rates are higher than normal but not high enough to classify as a mass extinction. Compare background extinction, mass extinction.
mass extinction
A catastrophic, widespread, often global event in which major groups of species are wiped out over a short time compared with normal (background) extinctions. Compare background extinction, mass depletion.
microevolution
The small genetic changes a population undergoes. Compare macroevolution.
mutagen
Chemical or form of radiation that causes inheritable changes (mutations) in the DNA molecules in the genes found in chromosomes. See carcinogen, mutation, teratogen.
mutation
A random change in DNA molecules making up genes that can yield changes in anatomy, physiology, or behavior in offspring. See mutagen.
natural rate of extinction
See background extinction.
natural selection
Process by which a particular beneficial gene (or set of genes) is reproduced in succeeding generations more than other genes. The result of natural selection is a population that contains a greater proportion of organisms better adapted to certain enviro
niche
See ecological niche.
realized niche
Parts of the fundamental niche of a species that are actually used by that species. See ecological niche, fundamental niche.
reproductive isolation
Long-term geographic separation of members of a particular sexually reproducing species.
specialist species
Species with a narrow ecological niche. They may be able to live in only one type of habitat, tolerate only a narrow range of climatic and other environmental conditions, or use only one type or a few types of food. Compare generalist species.
speciation
Formation of two species from one species because of divergent natural selection in response to changes in environmental conditions; usually takes thousands of years. Compare extinction.
theory of evolution
Widely accepted scientific idea that all life forms developed from earlier life forms. Although this theory conflicts with the creation stories of many religions, it is the way biologists explain how life has changed over the past 3.6-3.8 billion years an
transgenic organisms
See genetically modified organisms (GMOs).
water table
Upper surface of the zone of saturation, in which all available pores in the soil and rock in the earth's crust are filled with water.
wild species
Species found in the natural environment. Compare domesticated species.