Evolution, Population Genetics, and Speciation

Vocabulary flashcards covering principles of evolutionary biology, population genetics, modes of selection, speciation, evolutionary developmental biology (EvoDevo), phylogenetics, and evolutionary evidence.

Evolution (Microevolution)

A measurable change in allele frequencies over generations of time within a population of individuals.

Hardy-Weinberg Principle

The principle stating that allele and genotype frequencies in a population remain constant from generation to generation unless acted upon by outside agents such as mutation, migration, nonrandom mating, genetic drift, or natural selection.

Hardy-Weinberg Equation

The mathematical formula $p^2 + 2pq + q^2 = 1$ describing the relationship between allele and genotype frequencies, where $p^2$ represents the homozygous dominant genotype, $2pq$ represents the heterozygous genotype, and $q^2$ represents the homozygous recessive genotype.

Gene Flow

The movement of alleles from one population to another that occurs when individuals move between populations or when one population joins another with different allele frequencies.

Genetic Drift

The chance alteration of gene frequencies in a population, which most strongly affects small populations.

Bottleneck Effect

A form of genetic drift that occurs when a small subset of an original population survives a catastrophic dieback, drastically reducing genetic variation in the subsequent generations.

Founder Effect

A form of genetic drift occurring when a small subset of the original population becomes isolated or migrates to a new location, establishing a new population with different allele frequencies.

Sexual Selection

A mode of change driven by mate choice wherein members of a population prefer partners with particular phenotypes, sometimes leading to runaway selection for traits that enhance mating success despite reducing survival.

Natural Selection

The only known natural process leading to adaptive evolution, occurring when individuals with traits best suited to their environment survive and reproduce more successfully, increasing the frequency of those favorable alleles in the population.

Biological Fitness

A measure of an individual's lifetime fecundity (offspring produced) combined with the survival of those offspring to reproduce, often reflecting an evolutionary trade-off between survival and reproduction.

Modes of Selection

The three primary patterns of natural selection: stabilizing selection (favors intermediate phenotypes and constricts variance), directional selection (favors one phenotypic extreme and shifts the mean), and disruptive selection (favors both phenotypic extremes, producing two distinct peaks).

Industrial Melanism

The evolutionary shift in phenotypic coloration observed in organisms like the peppered moth (Biston betularia), where pollution-induced loss of lichens favored the dark (melanic) morph over the speckled form due to predation advantages.

Macroevolution

Evolutionary change occurring over vast expanses of time that is sufficient to transform one species into new species and produce higher taxonomic ranks such as genera, families, and orders.

Biological Species Concept

A definition of species as a group of like individuals that have the capacity to interbreed and produce viable, fertile offspring, focusing on genetic and reproductive barriers.

Ring Species

A connected series of neighboring populations distributed geographically around a barrier, where adjacent populations can interbreed, but the two terminal populations overlapping at the end of the ring are reproductively isolated and cannot interbreed.

Anagenesis

A pattern of speciation in which an entire ancestral population linearly transforms into a new species over time without branching.

Cladogenesis

A pattern of speciation where an ancestral lineage splits or branches into two or more distinct, independent descendant populations.

Pre-zygotic Isolating Mechanisms

Barriers that prevent mating or fertilization between populations, including geographic, ecological, temporal, behavioral, and mechanical isolation, as well as gametic incompatibility.

Post-zygotic Isolating Mechanisms

Reproductive isolating barriers that take effect after successful mating and fertilization, including hybrid inviability and hybrid infertility (e.g., mules).

Allopatric Speciation

The formation of new species resulting from spatial or geographic isolation that prevents gene flow between divided populations.

Sympatric Speciation

The emergence of new species within the same geographic area without physical barriers, driven by mechanisms such as polyploidy, niche partitioning, or behavioral polymorphisms.

Adaptive Radiation

The rapid diversification of a single ancestral population into multiple distinct descendant species filling diverse ecological niche spaces.

Convergent Evolution

The independent evolution of similar physical characteristics or adaptations (homoplasies) in unrelated lineages due to exposure to shared environmental pressures and lifestyles.

Parallel Evolution (Parallelism)

The process where two related lineages independently evolve common adaptations concurrently, frequently driven by shared developmental pathways and gene systems.

Evolutionary Developmental Biology (EvoDevo)

A biological discipline aimed at understanding ancestral evolutionary relationships and morphological changes through the lens of embryonic development and gene regulation.

Recapitulation Theory

Ernst Haeckel's historic, largely discredited hypothesis that 'ontogeny recapitulates phylogeny,' proposing that the embryonic developmental stages of an organism directly replay its evolutionary history.

Heterochrony

Evolutionary change in the timing, order, or rate of developmental events relative to an ancestor, categorized by parameters of onset, offset, and growth rate.

Allometry

Differential growth rates of distinct body parts or organs relative to the overall growth of an organism during development.

Neoteny

A form of heterochrony where the rate of somatic development is decelerated relative to reproductive development, causing sexually mature adult organisms to retain juvenile or larval characteristics (e.g., axolotls).

Hox Genes

A conserved set of developmental toolkit genes whose spatial and temporal alterations in expression pattern body segment identity and morphological complexity across diverse animal phyla.

Evolution of the Mammalian Middle Ear

A macroevolutionary transition in synapsids wherein ancestral reptilian jaw hinge bones (the articular and quadrate) gradually decreased in size and were co-opted into auditory ossicles (the malleus and incus).

Phylogenetic Tree

A branching diagram that illustrates the evolutionary history and relationships of related organisms, where branch points (nodes) signify speciation events and common ancestors.

Clade

A monophyletic group on a phylogenetic tree that consists of a common ancestor and all of its lineal descendants.

Wallace Effect (Reinforcement)

The evolutionary process wherein natural selection actively strengthens pre-zygotic isolating mechanisms between diverging populations because hybrid offspring suffer lower fitness.

Universal Common Descent

The foundational evolutionary concept stating that all organisms on Earth descended through modification from a single common ancestor known as the Last Universal Common Ancestor (LUCA).

Irreducible Complexity

An Intelligent Design argument claiming that complex biological systems require all constituent components to function simultaneously and therefore cannot evolve via stepwise natural selection.

Exaptation

An evolutionary process where a trait that originally evolved to serve one functional role is later recruited or co-opted by natural selection to serve an entirely new function (e.g., feathers evolving for thermoregulation or display before being adapted for flight).

Inverted Retina

An anatomical feature of the vertebrate eye where photoreceptors face backward toward the interior pigment layer and nerve fibers pass in front of the retina to exit via the optic nerve, creating an unavoidable blind spot.

Adaptive Landscape (Fitness Peak)

A 3D graphical model of fitness illustrating how populations climb peaks via natural selection and can become trapped on local, sub-optimal fitness peaks because crossing to a higher peak would require passing through intermediate maladaptive states.