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allopatric speciation

formation of a new species due to reduced gene flow in the presence of a geographic barrier

biological species concept

the idea that a species is defined in terms of their ability to reproduce in nature to form healthy, fertile offspring


a structure that contains DNA, the genetic material that is passed from one generation to the next

ecological species concept

the idea that a species is defined based on its ecological niche, which includes all the biotic and abiotic factors in the environment


all organisms living in one geographic region and all the environmental factors that affect those organisms

external fertilization

when sperm and egg fuse outside of a body in the environment

fossil record

all of the fossilized artifacts taken in the context of their placement within Earth's geological strata

gene flow

a change in the gene pool caused by individuals entering or leaving a population

gene pool

the total set of genes of all individuals in a population


a process of speciation that involves the accumulation of small genetic changes over a long period of time


an offspring produced when members of two species interbreed

hybrid zone

geographic region where two species overlap and the formation of hybrids occurs

internal fertilization

sperm and egg fuse inside a body


evolutionary change at or above the species level


a process in cell division during which the number of chromosomes decreases to half the original number by two divisions of the nucleus, resulting in the production of gametes


a change in allele frequencies within a population from one generation to the next


the process of cell division that results in two cells that are genetic clones of the parent cell

morphological species concept

the idea that a species is defined and characterized by body shape and structure


a change in DNA sequence


a condition in which an organism has more than the normal number of copies of a set of chromosomes


an interbreeding group of individuals of the same species

postzygotic barrier

a reproductive barrier to the development of a hybrid zygote into a healthy, fertile adult

prezygotic barrier

a reproductive barrier at the time of mating or fertilization that impedes the formation of a hybrid zygote

punctuated equilibrium

pattern in the fossil record in which a species undergoes long periods of no change, which are interrupted by large genetic changes over short periods of time

reproductive isolation

state in which reproductive barriers exist to prevent the formation of healthy, fertile offspring from individuals of two different species


the process through which a species evolves into two or more new species


a group of organisms that can reproduce in nature to form healthy, fertile offspring

sympatric speciation

formation of a new species in the absence of a geographic barrier to prevent gene flow


a fertilized egg