Evolutionary Biology Cheat Sheet

The core ideas of Evolutionary Biology distilled into a single, scannable reference — perfect for review or quick lookup.

PiqCue — piqcue.com/evolutionary-biology/cheatsheet

Quick Reference

Natural Selection

The process by which organisms with traits better suited to their environment tend to survive and reproduce at higher rates than those without such traits. Over many generations, this differential reproductive success causes favorable heritable traits to become more prevalent in a population.

Genetic Drift

Random fluctuations in allele frequencies within a population, particularly pronounced in small populations. Unlike natural selection, genetic drift is not driven by the adaptive value of traits but by chance events in reproduction and survival.

Speciation

The evolutionary process by which new biological species arise. Speciation can occur when populations become geographically isolated (allopatric speciation), when reproductive barriers develop within a shared habitat (sympatric speciation), or through other mechanisms such as polyploidy.

Adaptation

A heritable trait that has evolved through natural selection because it enhances an organism's fitness in its specific environment. Adaptations can be structural, physiological, or behavioral, and they accumulate incrementally over many generations.

Phylogenetics

The study of evolutionary relationships among groups of organisms, typically represented as branching diagrams called phylogenetic trees. Modern phylogenetics relies heavily on molecular data such as DNA and protein sequences to reconstruct the history of lineage divergence.

Gene Flow

The transfer of genetic material from one population to another through migration and interbreeding. Gene flow tends to reduce genetic differences between populations, counteracting the effects of natural selection and genetic drift that would otherwise cause divergence.

Sexual Selection

A form of natural selection in which individuals with certain traits are more successful at attracting mates, leading those traits to become more pronounced over generations. Sexual selection can operate through mate choice (intersexual selection) or competition between members of the same sex (intrasexual selection).

Coevolution

The process by which two or more species reciprocally influence each other's evolution over time. Coevolution can produce mutualistic relationships, predator-prey arms races, or tightly linked parasite-host dynamics.

Homology

The existence of shared ancestry between structures, genes, or traits in different species. Homologous structures may serve different functions in different organisms but share a common developmental and evolutionary origin, providing key evidence for common descent.

Hardy-Weinberg Equilibrium

A mathematical model describing a hypothetical population in which allele and genotype frequencies remain constant from generation to generation in the absence of evolutionary influences. It requires no mutation, no selection, random mating, infinite population size, and no gene flow.

Key Terms at a Glance

Allele: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.

Phenotype: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.

Genotype: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.

Fitness: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.

Mutation: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.

Population Genetics: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.

Clade: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.

Sympatric Speciation: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.

Allopatric Speciation: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.

Genetic Variation: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.

Macroevolution: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.

Microevolution: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.

Recombination: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.

Epigenetics: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.

Biogeography: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.

Get study tips in your inbox

We'll send you evidence-based study strategies and new cheat sheets as they're published.

We'll notify you about updates. No spam, unsubscribe anytime.