- adaptive evolution
- increase in frequency of beneficial alleles and decrease in deleterious alleles due to selection
- allele frequency
- (also, gene frequency) rate at which a specific allele appears within a population
- assortative mating
- when individuals tend to mate with those who are phenotypically similar to themselves
- bottleneck effect
- magnification of genetic drift as a result of natural events or catastrophes
- cline
- gradual geographic variation across an ecological gradient
- directional selection
- selection that favors phenotypes at one end of the spectrum of existing variation
- diversifying selection
- selection that favors two or more distinct phenotypes
- evolutionary fitness
- (also, Darwinian 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)
- gene flow
- flow of alleles in and out of a population due to the individual or gamete migration
- gene pool
- all the alleles that the individuals in the population carry
- genetic drift
- effect of chance on a population’s gene pool
- genetic structure
- distribution of the different possible genotypes in a population
- genetic variability
- diversity of alleles and genotypes in a population
- geographical variation
- differences in the phenotypic variation between populations that are separated geographically
- good genes hypothesis
- theory of sexual selection that argues individuals develop impressive ornaments to show off their efficient metabolism or ability to fight disease
- handicap principle
- theory of sexual selection that argues only the fittest individuals can afford costly traits
- heritability
- fraction of population variation that can be attributed to its genetic variability
- honest signal
- trait that gives a truthful impression of an individual’s fitness
- inbreeding
- mating of closely related individuals
- inbreeding depression
- increase in abnormalities and disease in inbreeding populations
- macroevolution
- broader scale evolutionary changes that scientists see over paleontological time
- microevolution
- changes in a population’s genetic structure
- modern synthesis
- overarching evolutionary paradigm that took shape by the 1940s and scientists generally accept today
- nonrandom mating
- changes in a population’s gene pool due to mate choice or other forces that cause individuals to mate with certain phenotypes more than others
- population genetics
- study of how selective forces change the allele frequencies in a population over time
- population variation
- distribution of phenotypes in a population
- relative fitness
- individual’s ability to survive and reproduce relative to the rest of the population
- selective pressure
- environmental factor that causes one phenotype to be better than another
- sexual dimorphism
- phenotypic difference between a population's males and females
- stabilizing selection
- selection that favors average phenotypes