Natural Selection, Sexual Selection, and Modes of Selection

Vocabulary practice flashcards covering core evolutionary concepts including adaptation constraints, sexual selection types, artificial selection, and the four modes of phenotypic selection.

Historical constraints

Restrictions on evolutionary adaptations resulting from a species' evolutionary history, requiring new traits to be modified from pre-existing ancestral structures rather than constructed from scratch.

Trade-off

An evolutionary compromise where an advantage gained in one context comes at the expense of a disadvantage in another, such as increasing survivorship $s$ at the expense of fecundity $f$.

Panglossian paradox

The mistaken assumption that every feature or trait of an organism is an adaptation designed to serve a specific, optimal function.

Sexual selection

A form of selection operating on traits that determine an individual's ability to obtain mates and successfully reproduce, turning $f$ from zero into a non-zero number.

Intrasexual selection

Selection involving direct competition among individuals of the same sex (typically male-male competition) for access to mates of the opposite sex.

Intersexual selection

Selection occurring between individuals of different sexes, typically involving female choice based on specific phenotypic traits or showy displays of males.

Honest indicator

A showy phenotypic trait or display that reliably signals an individual's overall genetic fitness, health, or resource-providing potential to prospective mates.

Sexual dimorphism

Systematic differences in physical appearance, morphology, or size between males and females of the same species.

Artificial selection

A process of selective breeding in which humans consciously select specific individuals to survive and reproduce based on desired traits.

Directional selection

A mode of selection favoring individuals at one extreme of a phenotypic distribution, causing the mean trait value of the population to shift in that direction over generations.

Stabilizing selection

A mode of selection favoring intermediate phenotypes over extreme phenotypes, reducing overall phenotypic variation without altering the mean trait value.

Disruptive selection

A mode of selection favoring individuals at both extreme ends of a trait distribution over intermediate phenotypes, increasing variation and potentially leading to speciation.

Balancing selection

A category of natural selection that maintains multiple phenotypic variants or alleles in a population rather than fixing a single optimal phenotype.

Heterozygote advantage

A type of balancing selection in which heterozygous individuals have higher relative fitness than either homozygous dominant or homozygous recessive individuals.

Negative frequency-dependent selection

A type of balancing selection where the relative fitness of a phenotype or allele increases when it is rare in a population and decreases as it becomes common.