Evolution of Populations, Speciation, and the History of Life

Comprehensive vocabulary flashcards covering evolutionary mechanisms, speciation concepts, phylogenetics, molecular clocks, and the history and origins of life on Earth.

Microevolution

Changes in allele frequencies within a population over time, caused by natural selection, genetic drift, and gene flow.

Genetic Variation

Differences among individuals based on their genetic composition, which can be measured by the average percentage of heterozygous genes or nucleotide variation.

Mutation

A change in an organism's nucleotide sequence that creates new alleles and genes.

Population

A group of individuals of the same species that live in the same area and interbreed.

Hardy-Weinberg Equilibrium

A state in which allele frequencies in a population remain constant over time, demonstrating that genetic variation alone does not guarantee evolution.

Natural Selection

A process where individuals with certain heritable traits survive and reproduce at higher rates than others, directly resulting in adaptation.

Speciation

The evolutionary process by which one species splits into two distinct species.

Macroevolution

Patterns of evolutionary change above the species level, examined through interspecific similarities and differences.

Biological Species Concept

A species definition stating that members of a species are populations that interbreed in nature, produce viable offspring, and cannot produce viable offspring with other groups.

Reproductive Isolation

The existence of biological barriers that prevent members of different species from interbreeding and producing viable offspring.

Prezygotic Barriers

Mechanisms that impede mating before fertilization occurs or hinder fertilization itself.

Habitat Isolation

A prezygotic barrier where two species occupy different habitats within the same general area and rarely encounter one another.

Temporal Isolation

A prezygotic barrier where species mate or breed at different times of day, seasons, or years.

Behavioral Isolation

A prezygotic barrier where species have differing mating rituals and courtship behaviors that prevent interbreeding.

Mechanical Isolation

A prezygotic barrier where morphological differences prevent successful copulation or mating from occurring.

Gametic Isolation

A prezygotic barrier where the sperm of one species cannot successfully fertilize the eggs of another species.

Postzygotic Barriers

Barriers that prevent hybrid zygotes from developing into viable, fertile adults.

Reduced Hybrid Viability

A postzygotic barrier where genes from different parent species interact in ways that impair the hybrid offspring's survival or development.

Reduced Hybrid Fertility

A postzygotic barrier where meiosis fails to produce normal gametes because chromosomes differ in number or structure, rendering the hybrid sterile.

Hybrid Breakdown

A postzygotic barrier where first-generation hybrids are viable and fertile, but the offspring of subsequent generations become progressively weaker and sterile.

Hybrid Zone

A region where members of different species meet, mate, and produce offspring of mixed ancestry due to incomplete reproductive barriers.

Reinforcement

The evolutionary process where prezygotic barriers are progressively selected for and strengthened over time to reduce the production of unfit hybrids.

Fusion

A process where hybrids are more fit than the parent species, causing reproductive barriers to break down and the two species to fuse into a single distinct population.

Stability (Hybrid Zone)

A condition where a hybrid population continues to persist over time despite being less fit, typically sustained because parent organisms continuously migrate into the hybrid zone.

Morphological Species Concept

A concept that distinguishes and classifies species based on structural differences and physical traits.

Ecological Species Concept

A concept that defines a species based on a one-to-one correlation with its ecological niche.

Phylogenetic Species Concept

A concept that defines a species as a group of organisms that all share a single common ancestor and unique evolutionary ancestry.

Allopatric Speciation

Speciation that occurs when populations become geographically isolated from one another, which leads to reproductive isolation.

Sympatric Speciation

Speciation that occurs when populations are not geographically isolated, typically driven by polyploidy mutations, sexual selection, or habitat differentiation.

Taxonomy

The process of naming and classifying organisms, originally developed by Carl Linnaeus into a hierarchical system.

Binomial Nomenclature

The standard two-part naming convention that specifies the genus and species of a given organism.

Paraphyletic Group

A clade that includes an ancestral species and only some of its descendants that share a specified similar trait.

Polyphyletic Group

A grouping of organisms that share similar physical traits or habitats but originate from different ancestral lineages, omitting their most recent common ancestor.

Monophyletic Group

A clade consisting of a single common ancestor and all of its descendants.

Homologies

Similarities between organisms, whether genetic or structural, resulting from shared ancestry.

Molecular Systematics

A discipline that uses nucleotide sequences of genetic material that does not change with reproduction to determine evolutionary relationships.

Maximum Parsimony

The phylogenetic principle stating that the simplest tree with the least number of evolutionary events or branches is the preferred hypothesis.

Analogous Structures

Similar anatomical structures across species that share no recent common ancestor, having evolved independently through convergent evolution.

Gene Families

Groups of related genes within a genome that arise through gene duplication events.

Orthologous Genes

Homologous genes found in two separate species that diverged as a result of a speciation event.

Paralogous Genes

Homologous genes that result from gene duplication within a single species, such as olfactory receptor genes, which do not create speciation.

Molecular Clock

An approach used to estimate the timeframe of evolutionary events based on the premise that certain genes accumulate nucleotide substitutions at a constant rate.

Hadean Period

The first $0.5\text{ billion}$ years after Earth's formation, which established liquid water and an atmosphere responsible for the first organic compounds.

Miller-Urey Experiment

An experiment demonstrating that organic molecules could form abioticly from an atmosphere simulating early Earth conditions.

Protocells

Fluid-filled vesicles with a membrane-like structure theorized to have possessed early forms of replication and metabolism.

LUCA

The Last Universal Common Ancestor; a construct used to make phylogenetic trees straightforward rather than the very first form of life.

Radiometric Dating

A method used to determine the numerical age of fossils based on the radioactive decay of isotopes.

Anagenesis

A pattern of evolution involving continuous, progressive transformation of a single lineage over time without branching.

Punctuated Equilibrium

An evolutionary model characterized by long periods of stasis interrupted by rapid bursts of speciation and change.

Stromatolites

Layered rocks formed when prokaryotes bind thin films of sediment together, first appearing roughly $3.5\text{ billion}$ years ago as the earliest known fossils.

Endosymbiosis

The evolutionary process where an ancestral cell engulfed a smaller bacterium that eventually evolved into an organelle, such as the mitochondrion.

Cambrian Explosion

A period of rapid diversification in multicellular organisms, particularly those possessing simple skeletons.

Adaptive Radiation

The rapid diversification of a single lineage into a variety of forms following the sudden availability of ecological niches.

Horizontal Gene Transfer

The transmission of genetic material between organisms independently of reproduction, such as through transformation.

Hox Genes

Homeotic genes that determine the timing and spatial patterns of developmental gene expression in an organism.

Heterochrony

An evolutionary change in the timing or rate of developmental processes relative to an ancestral state.

Paedomorphosis

A developmental acceleration of reproductive organs relative to non-reproductive structures, leading an adult organism to retain juvenile physical features.