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natural selection

A process in which individuals with certain inherited traits survive and reproduce at higher rates than others because of those traits.

Affect of natural selection

Changes in phenotypic allele frequency in a population.

Gene flow

Movement of alleles from one population to another when individuals migrate and reproduce.

Mutation

A change in a DNA sequence that affects genetic information; the ultimate source of genetic variation.

genetic drift

Random change in allele frequencies that occurs in small populations.

Fitness

The reproductive success of an individual relative to the average reproductive success of the population.

bottleneck effect

A reduction in a population’s size that decreases genetic diversity.

founder effect

Change in allele frequencies due to the migration of a small subgroup of a population.

vestigial structures

Structures that are present in an organism but no longer serve their original function.

homologous structures

Structures shared by related species that come from a common ancestor.

analogous structures

Similar features in unrelated species that evolved due to similar environmental pressures.

Hardy-Weinberg equilibrium

A state in which allele frequencies remain constant over time.

Hardy-Weinberg equation

p² + 2pq + q² = 1.

directional selection

Natural selection that favors one extreme variation of a trait.

stabilizing selection

Natural selection that favors intermediate traits and selects against extremes.

disruptive selection

Natural selection in which individuals with extreme traits have higher fitness than those with intermediate traits.

convergent evolution

Unrelated species independently evolve similar traits due to similar environmental pressures.

divergent evolution

Species sharing a common ancestor evolve and become more different over time.

artificial selection

Human-driven breeding of organisms to produce offspring with specific traits; changes occur rapidly.

Archaeopteryx

An intermediate fossil showing both dinosaur and bird characteristics.

Biogeography

Study of how species are distributed geographically and how island species often resemble mainland relatives.

molecular clock

A method using DNA comparisons to estimate how long two species have been evolving separately.

Evidence of Evolution

Fossils, embryology, homologous structures, DNA comparisons, and vestigial structures.

Gradualism

Evolution occurs slowly and steadily over long periods.

punctuated equilibrium

Long periods of stability interrupted by brief rapid evolutionary changes.

allopatric speciation

Formation of new species due to geographic isolation.

sympatric speciation

Formation of new species within the same geographic area.

prezygotic isolation

Barriers that prevent mating or fertilization before zygote formation.

ecological isolation

Species live in the same region but occupy different habitats.

behavioral isolation

Differences in courtship behaviors prevent interbreeding.

temporal isolation

Species reproduce at different times.

mechanical isolation

Physical differences prevent mating.

prevention of gamete fusion

Gametes of different species cannot fuse successfully.

postzygotic isolation

Reproductive isolation occurring after fertilization; hybrids typically cannot reproduce.

hybrid sterility

Hybrids are infertile or fail to reach adulthood.

Biological Species Concept (BSC)

Species are groups of interbreeding populations that are reproductively isolated from others.

phylogenetic species concept

Defines a species as the smallest group sharing a common ancestor, forming one branch of a phylogenetic tree.

Autopolyploidy

Chromosome duplication within a single species, forming tetraploids that can self-fertilize or mate with other tetraploids.

allopolyploidy

Polyploidy formed from chromosome contributions of two different species.

Systematics

Study of biological diversity and evolutionary relationships.

Phylogeny

The evolutionary history and relationships among species.

derived characters

Traits appearing in recent lineage members but not in older ancestors.

Clade

A group that includes an ancestor and all its descendants.

Synapomorphies

Shared derived traits of a clade.

Plesiomorphies

Ancestral character states.

Symplesiomorphies

Shared ancestral traits.

polyphyletic group

A group containing species without a recent common ancestor.

monophyletic group

A group consisting of an ancestor and all its descendants.

Homoplasy

Independent evolution of similar traits in unrelated lineages.

Endosymbiosis

Theory that early eukaryotes arose from prokaryotes living inside other cells; origin of mitochondria and chloroplasts.