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Group of individuals of the same species in a specified area

Gene Pool

Pool of genetic resources


Different forms of genes in a gene pool (in a sexually reproducing population)

Lethal Mutation

Mutation that drastically changes phenotype, usually results in death

Neutral Mutation

Mutation that changes the base sequence of DNA, but the alteration has no effect on survival or reproduction--neither helps nor hurts the individual

Allele Frequencies

The relative abundances of alleles of a given gene among all individuals of a population, starting from a theoretical reference point

Genetic Equilibrium

A theoretical reference point which occurs when a population is not evolving with respect to the gene


Of a population or species, small-scale change in allele frequencies. Occurs by mutation, natural selection, genetic drift, gene flow

Natural Selection

Differential survival and reproduction among individuals of a population that vary in the details of their shared traits. Influences the frequency of alleles in a population by operating on phenotypes that have a genetic basis.

Directional Selection

Allele frequencies shift in a consistent direction, so forms at one end of a range of phenotypic variation become more common over time.

Stabilizing Selection

An intermediate form of a trait is favored, and extreme forms are not

Disruptive Selection

Forms of a trait at both ends of a range of variation are favored, and intermediate forms are selected against

Sexual Dimorphism

Having distinct male and female phenotypes

Sexual Selection

Mode of natural selection in which some individuals, the genetic winners, out-reproduce others of a population because they are better at securing mates. Most adaptive forms of a trait are those that help individuals defeat same-sex rivals for mates, or are the ones most attractive to the opposite sex.

Balanced Polymorphism

The maintenance of two or more alleles for a trait in some populations, as a result of natural selection against homozygotes

Genetic Drift

Random change in allele frequencies over time, brought about by chance alone


This happens when all individuals of a population are homozygous for one allele


A drastic reduction in population size brought about by severe pressure

Founder Effect

A form of bottlenecking. Change in allele frequencies that occurs after a few individuals establish a new population


Breeding or mating between close relatives, which share a large number of alleles

Gene Flow

The movement of alleles among populations

Reproductive Isolation

Any mechanism that prevents gene flow between populations. Part of speciation


Formation of daughter species from a population or subpopulation of a parent species; the routes vary in their details and duration

Allopatric Speciation

A speciation mode by which a physical barrier separates two population and ends the gene flow between them. Then reproductive isolation mechanisms arise

Sympatric Speciation

A speciation mode by which new species form within the home range of an existing species, in the absence of a physical barrier

Parapatric Speication

A speciation mode in which different selection pressures lead to divergences within a single population. May occur when one population extends across a broad region encompassing diverse habitats


Evolutionary patterns on a larger scale


The process by which close ecological interatctions between two species cause them to evolve jointly


A lineage persists for millions of years with little or no change


Adaptation of an existing structure for a completely diffferent purpose; a major evolutionary novelty

Adaptive Radiation

A burst of divergences from a single lineage

Key Innovation

A structural or functional modification that bestows upon its bearer the opportunity to exploit a habitat more efficiently or in a novel way


Irrevocably lost from the Earth

Mass Extinctions

Losses of many lineages

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