adaptation

heritable trait or behavior in an organism that aids in its survival and reproduction in its present environment

allele frequency

rate at which a specific allele appears within a population

allopatric speciation

speciation that occurs via geographic separation

allopatry

occurring in different geographic areas

artificial selection

deliberate manipulation of fitness by humans through selective breeding

behavioral isolation

type of reproductive isolation that occurs when a specific behavior or lack of one prevents reproduction from taking place

biological species concept

species concept based on reproductive isolation

bottleneck effect

magnification of genetic drift as a result of natural events or catastrophes

directional selection

selection that favors phenotypes at one end of the spectrum of existing variation

dispersal

movement of individuals to a new geographic area

diversifying selection

selection that favors two or more distinct phenotypes

evolution

change in allele frequencies of a population across generations

fitness

individual’s ability to survive and reproduce

founder effect

event that initiates an allele frequency change in part of the population, which is not typical of the original population

frequency-dependent selection

selection that favors phenotypes that are either common (positive frequency-dependent selection) or rare (negative frequency-dependent selection)

fusion

upon reconnection, reproductive barriers weaken and the two lineages become one

gametic isolation

type of reproductive isolation that occurs when differences in gametic cells (egg and sperm) prevent successful fertilization

genetic drift

effect of chance on a population’s gene pool

good genes hypothesis

theory of sexual selection that argues individuals develop impressive ornaments to show off their efficient metabolism or ability to fight disease

Grant, Peter and Rosemary

studied Darwin’s finches on the Galapagos Islands and measured evolution by natural selection over short time scales

habitat isolation

reproductive isolation resulting when species' populations move or are moved to a new habitat, taking up residence in a place that no longer overlaps with the same species' other populations

handicap principle

theory of sexual selection that argues only the fittest individuals can afford costly traits

heredity

transmission of genetic characteristics from parents to offspring

heritability

fraction of population variation that can be attributed to its genetic variance

honest signal

trait that gives a truthful impression of an individual’s fitness

hybrid

offspring of two closely related individuals, not of the same species

hybrid inviability

type of reproductive isolation that occurs when hybrids do not survive to sexual maturity

hybrid sterility

type of reproductive isolation that occurs when hybrids are viable but biologically or ecologically sterile

hybrid zone

area where two closely related species continue to interact and reproduce, forming hybrids

mechanical isolation

type of reproductive isolation that occurs when differences in the size or shape of reproductive organs makes successful mating impossible

Mendel, Gregor

geneticist who first described many characteristics of heredity

migration (gene flow)

transfer of alleles from one population to another, making populations more similar

monophyletic group (clade)

a group that consists of one ancestor and all of its descendants

morphological species concept

species concept based on differences in size, shape, or other morphological attributes

mutation

changes to an organism’s DNA; changes may be neutral or deleterious depending on their effect on fitness

natural selection

the non-random and differential reproduction of different genotypes acting to preserve favorable variants and eliminate less favorable variants

phylogenetic species concept

species concept based on identifying the smallest sets of monophyletic groups in a phylogeny

phylogeny (phylogenetic tree)

representation of the evolutionary relationships among organisms

pleiotropy

when a single gene affects multiple traits

polygenic trait

a trait controlled by multiple genes

postzygotic barrier

reproductive isolation mechanism that occurs after zygote formation

prezygotic barrier

reproductive isolation mechanism that occurs before zygote formation

reinforcement

continued speciation divergence between two related species due to low fitness of hybrids between them

relative fitness

individual’s ability to survive and reproduce relative to the rest of the population

reproductive isolation

situation in which a species is reproductively independent from other species due to behavioral, geographic, or reproductive barriers

selective pressure

environmental factor that causes one phenotype to be more favorable than another

sexual dimorphism

phenotypic difference between males and females in a population

sexual selection

selection that favors phenotypes that increase ability to obtain or choose mates

species

group of populations that interbreed and produce fertile offspring

species concept

a set of criteria used to define and differentiate species

speciation

formation of a new species

stabilizing selection

selection that favors average phenotypes

temporal isolation

differences in breeding schedules that act as a prezygotic barrier leading to reproductive isolation

vicariance

physical splitting of a population into smaller isolated populations by a physical barrier