Evolutionary Biology Glossary

One of two or more versions of a gene that arise by mutation and are found at the same locus on a chromosome. Different alleles can result in different observable phenotypic traits.

The formation of new species when populations are geographically separated by a physical barrier such as a mountain range, river, or ocean, preventing gene flow and allowing independent divergence.

Body parts in different organisms that serve similar functions but evolved independently rather than from a common ancestor. They arise through convergent evolution in response to similar environmental pressures.

The study of the distribution of species and ecosystems in geographic space and through geological time. Biogeographic patterns provide important evidence for evolution and help explain why certain organisms are found only in specific regions.

A group of organisms that includes a common ancestor and all of its descendants, representing a single branch on the tree of life. Clades are the fundamental units of phylogenetic classification.

A symbiotic relationship in which one organism lives inside the cells of another. The endosymbiotic theory explains the origin of mitochondria and chloroplasts as formerly free-living bacteria incorporated into ancestral eukaryotic cells.

The study of heritable changes in gene expression that do not involve alterations to the DNA sequence itself. Epigenetic mechanisms, such as DNA methylation and histone modification, can be influenced by environmental factors.

The complete disappearance of a species when the last individual of that species dies. Mass extinctions have occurred at least five times in Earth's history and have profoundly shaped the trajectory of evolution by opening ecological niches.

The relative ability of an organism to survive and transmit its genes to the next generation. Measured by reproductive success, fitness is the central concept linking natural selection to evolutionary change.

The differences in DNA sequences among individuals within a population. It is the foundation upon which natural selection and other evolutionary forces act and arises through mutation, recombination, and gene flow.

The genetic constitution of an organism, specifically the combination of alleles it carries at one or more loci. The genotype, together with environmental factors, determines the phenotype.

Having two different alleles at a particular gene locus on homologous chromosomes. Heterozygous individuals can produce two types of gametes and may express intermediate or dominant phenotypes.

Having two identical alleles at a particular gene locus on homologous chromosomes. An organism that is homozygous for a trait will produce only one type of gamete for that locus.

Evolutionary change at or above the species level, including the origin of new species, the formation of new higher taxa, and large-scale patterns in the history of life such as mass extinctions and adaptive radiations.

Evolutionary changes in allele frequencies that occur within a population over relatively short periods of time. These small-scale changes are driven by natural selection, genetic drift, mutation, and gene flow.

A permanent alteration in the DNA sequence of a gene or chromosome. Mutations are the ultimate source of all genetic variation and can be neutral, beneficial, or harmful to the organism.

The ecological role and position of a species within its environment, including its habitat, diet, activity patterns, and interactions with other species. Niches define how organisms utilize resources and respond to conditions.

The set of observable characteristics or traits of an organism resulting from the interaction of its genotype with the environment, including morphology, behavior, and physiology.

A field that studies the geographic distribution of genetic lineages within and among closely related species, integrating phylogenetics with biogeography to understand the historical processes shaping current distributions.

The occurrence of two or more distinct forms, stages, or types in a population of a species. Genetic polymorphism refers to the existence of multiple alleles at a locus with the least common allele maintained above a frequency of 1%.

The branch of genetics that studies the distribution and change of allele frequencies in populations, using mathematical models to understand how evolution occurs at the genetic level.

The process by which DNA molecules exchange genetic information during meiosis, producing new combinations of alleles on chromosomes. Recombination is a major source of genetic variation in sexually reproducing organisms.

Any environmental factor that influences the survival and reproductive success of organisms, thereby driving natural selection. Selective pressures include predation, competition, disease, climate, and food availability.

The formation of new species from a single ancestral species while inhabiting the same geographic region, often driven by ecological specialization, polyploidy, or disruptive selection.

The science of naming, describing, and classifying organisms into groups based on shared characteristics and evolutionary relationships. Modern taxonomy integrates morphological, molecular, and phylogenetic data.