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Variability
| Term | Definition |
|---|---|
| genetic equilibrium | A population in which the frequency of alleles remains the same over generations |
| gene flow | The movement of genes within a population or between two or more populations, creating new combinations of genes or alleles in individuals. A source of variation in the process of natural selection. |
| gene pool | The total number of alleles in a population. |
| stabilising selection | A selection pressure that culls the extremes in a population, maintaining the status quo. |
| bottleneck event | 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. |
| succession | The compositional change in an ecological community over time. Succession occurs after some major, or minor, disturbance has disrupted the previous composition of the community. |
| disruptive (diversifying) selection | A selection pressure that stimulates the allel frequency of opposite extremes. Peppered moths are an example. |
| genetic drift | Evolutionary change over generations due to random events in small populations. Changes in the frequencies of alleles in a population that occur by chance, rather than because of natural selection. |
| divergent evolution | A kind of evolutionary change that results in increasing morphological difference between initially more similar lineages. |
| derived character | A newer characteristic that has been inherited from a common ancestor, which distinguishes it from other potentially related organisms. |
| 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. |
| population density | The number of individuals of a species in an environment divided by the total land area, or water volume, of that environment. |
| niche | An organism's role in an environment, including how it uses its resources, relates to other organisms, and times its reproduction. |
| natural selection | The process by which favorable traits become more common within a population by passing them on to the next generation that increases the likelihood of the survival of the individuals that possess that trait. |
| symbiosis | An interaction between individuals of different species. Symbiotic relationships include mutualism, parasitism, and commensalism. They do not include predator-prey interactions. |
| fitness | The ability of an individual to successfully pass on its genes to the next generation. It has two components: survival (viability) and reproductive success (fecundity). |
| 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. If the population becomes isolated, results in speciation. |
| 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. |
| inheritance of acquired characters (Lamarck) | Historically influential but factually erroneous theory that an individual inherits characters that its parents acquired during their lifetimes. |
| Intelligent design | The non-scientific argument that complex biological structures have been designed by an unidentified supernatural or extraterrestrial intelligence. |
| population | A group of organisms, usually a group of sexual organisms that interbreed and share a gene pool. |
| reproductive isolation | Two populations or individuals of opposite sex are considered reproductively isolated from one another if they cannot together produce fertile offspring. |
| selective pressure | Environmental forces such as scarcity of food or extreme temperatures that result in the survival of only certain organisms with characteristics that provide resistance. |
| species | The largest group of organisms in which two individuals can produce fertile offspring, typically by sexual reproduction. |
| transitional fossil | Evidence that combines some traits of older, ancestral species with traits of more recent species (for instance; the evolution of fully aquatic whales from terrestrial ancestors). |
| habitat | The physical environment where a population of a single species lives, or inhabits. A habitat consists of all the abiotic, or nonliving, resources influencing the population. |
| community | A group of two or more populations of organisms from different species inhabiting the same location at the same time. Communities are composed only of biotic factors, aka living organisms. |
| competition | An interaction where individuals of different species—interspecific competition—or the same species—intraspecific competition—vie for limited resources. |
| commensalism | A symbiotic (read: long-term and partly beneficial) relationship between organisms, where one organism benefits from the relationship, and the other receives no harm or benefit. |
| carrying capacity | The maximum number of individuals in a single population that a given environment can sustain at a given time. |
| keystone species | A species in a community that has an effect on the community larger than one would expect based on the population size of that species. |
| mutualism | A symbiotic relationship where both organisms benefit. A common example is the relationship between pollinators and the plants they pollinate. |
| parasitism | A type of symbiotic relationship where one organism benefits and the other organism, the host, is harmed. |
| directional selection | A selection pressure that shifts the phenotype of a population in one certain direction. |
| analogous structure | 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 |
| vestigial structure / organ / feature | An anatomical feature (or behavior) that no longer seems to have a purpose in the current form of an organism of the given species. such as the whale pelvis or the human appendix. |
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misoest
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