Natural Selection

A process in which individuals that have certain inherited traits tend to survive and reproduce at higher rates than other individuals because of those traits.

Adaptation

inherited characteristic that increases an organism's chance of survival

Descent with modification

principle that each living species has descended, with changes, from other species over time

Homology

Similarity in characteristics resulting from a shared ancestry.

Analogy

similarities among unrelated species that result from convergent evolution

Vestigial Structures

remnant of a structure that may have had an important function in a species' ancestors, but has no clear function in the modern species.

Convergent Evolution

Process by which unrelated organisms independently evolve similarities when adapting to similar environments

Divergent Evolution

when two or more species sharing a common ancestor become more different over time

Adaptive Radiation(Divergent Evolution)

An evolutionary pattern in which many species evolve from a single ancestral species

Biogeography

Study of past and present distribution of organisms

Endemic Species

species that are native to and found only within a limited area

Phylogeny

Evolutionary history of a species or group of species.

Genus

group of closely related species; the first part of the scientific name in binomial nomenclature

Microevolution

Evolutionary change below the species level; change in the allele frequencies in a population over generations.

Macroevolution

large-scale evolutionary changes that take place over long periods of time

Species

A group of similar organisms that can breed and produce fertile offspring.

Speciation

the formation of new and distinct species in the course of evolution.

Reproductive Isolation

Separation of species or populations so that they cannot interbreed and produce fertile offspring

Prezygotic Barriers

A reproductive barrier that impedes mating between species or hinders fertilization if interspecific mating is attempted

Habitat Isolation

Two species encounter each other rarely, or not at all, because they occupy different habitats, even though not isolated by physical barriers

Temporal Isolation

form of reproductive isolation in which two populations reproduce at different times

Behavioral Isolation

isolation between populations due to differences in courtship or mating behavior

Mechanical Isolation

mating is attempted, but morphological differences prevent its successful completion

Gametic Isolation

Sperm of one species may not be able to fertilize eggs of another species

Postzygotic Barriers

Barriers that prevent the hybrid zygote from becoming a fertile adult.

Allopatric Speciation

The formation of a new species as a result of an ancestral population's becoming isolated by a geographic barrier.

Sympatric Speciation

The formation of a new species as a result of a genetic change that produces a reproductive barrier between the changed population (mutants) and the parent population. No geographic barrier is present.

Genetic Variation

Differences among individuals in the composition of their genes or other DNA segments

Population

A group of individuals that belong to the same species and live in the same area

Gene Pool

All the genes, including all the different alleles for each gene, that are present in a population at any one time

Genetic Drift

A change in the allele frequency of a population as a result of chance events rather than natural selection.

Bottleneck Effect

A change in allele frequency following a dramatic reduction in the size of a population

Founder Effect

Genetic drift that occurs when a few individuals become isolated from a larger population and form a new population whose gene pool composition is not reflective of that of the original population.

Gene Flow

Movement of alleles into or out of a population due to the migration of individuals to or from the population

Fitness

how well an organism can survive and reproduce in its environment

Stabilizing Selection

Natural selection that favors intermediate variants by acting against extreme phenotypes

Directional Selection

Form of natural selection in which the entire curve moves; occurs when individuals at one end of a distribution curve have higher fitness than individuals in the middle or at the other end of the curve

Disruptive Selection

natural selection in which individuals at the upper and lower ends of the curve have higher fitness than individuals near the middle of the curve

Sexual Selection

A form of natural selection in which individuals with certain inherited characteristics are more likely than other individuals to obtain mates.

Artificial Selection

Selection by humans for breeding of useful traits from the natural variation among different organisms

Extinction

A term that typically describes a species that no longer has any known living individuals.

Punctuated Equilibrium

Pattern of evolution in which long stable periods are interrupted by brief periods of more rapid change

Phylogenetic Tree

A family tree that shows the evolutionary relationships thought to exist among groups of organisms

Gradualism

The theory that evolution occurs slowly but steadily

Alleles

Different forms of a gene

Hardy-Weinberg Equilibrium

condition that occurs when the frequency of alleles in a particular gene pool remain constant over time

Conditions for Hardy-Weinberg Equilibrium

1. No mutations
2. Random mating
3. No natural selection
4. Extremely large population size
5. No gene flow

Hardy-Weinberg Equation

p^2 + 2pq + q^2 = 1, where p is the frequency of the dominant allele and q is the frequency of the recessive allele. It predicts the frequency of homozygous dominants, homozygous recessives, and heterozygotes.

p

frequency of dominant allele

q

frequency of recessive allele

p^2

frequency of homozygous dominant genotype

2pq

frequency of heterozygous genotype

q^2

frequency of homozygous recessive genotype