Evolution Calculators

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Evolution is the change in heritable characteristics of biological populations over successive generations. The modern evolutionary synthesis combines Darwin's natural selection with Mendelian genetics and molecular biology. The five mechanisms of evolutionary change are: natural selection (differential survival and reproduction based on heritable traits), genetic drift (random allele frequency changes in finite populations), mutation (creation of new heritable variation), gene flow (movement of alleles between populations), and non-random mating. Evolution operates on variation generated by mutation and recombination, filtered by natural selection and drift across deep time scales.

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Five Mechanisms of Evolution

  • Natural selection: differential survival and reproduction due to heritable traits; directional, stabilizing, or disruptive selection; the only mechanism that generates adaptation
  • Genetic drift: random allele frequency change in finite populations; stronger in small populations; causes loss of diversity (bottlenecks, founder effects)
  • Mutation: ultimate source of all new variation; creates new alleles; rate ≈ 10⁻⁸–10⁻⁹ per base per generation in DNA organisms; higher in RNA viruses
  • Gene flow: movement of alleles between populations through migration; homogenizes allele frequencies; counteracts local adaptation and drift
  • Non-random mating: sexual selection; assortative mating; inbreeding — changes genotype but not allele frequencies (except inbreeding effects)

Hardy-Weinberg Principle

A population is NOT evolving if: allele frequencies remain constant across generations → p² + 2pq + q² = 1. Deviation from HWE indicates evolution (selection, drift, gene flow, non-random mating).

Speciation

Allopatric: geographic isolation → divergence → reproductive isolation → new species. Sympatric: reproductive isolation without geographic separation. Biological species concept: species = groups capable of interbreeding and producing fertile offspring.

Glossary

Evolution
Change in heritable characteristics of populations over generations; driven by natural selection, genetic drift, mutation, gene flow, and non-random mating; the unifying theory of biology.
Natural Selection
Differential survival and reproduction based on heritable traits; requires variation, heritability, and fitness differences; the only evolutionary mechanism consistently producing adaptation.
Hardy-Weinberg Principle
In ideal populations allele frequencies remain constant: p² + 2pq + q² = 1; serves as the null model for evolution; deviation indicates selection, drift, gene flow, or non-random mating.

Frequently Asked Questions

Evolution is change in the heritable characteristics of a population over generations. Five mechanisms: (1) Natural selection: differential reproduction based on heritable traits — the only evolutionary mechanism that consistently produces adaptation to the environment. (2) Genetic drift: random fluctuation in allele frequencies due to sampling variation in finite populations — causes loss of diversity in small populations. (3) Mutation: changes in DNA sequence creating new alleles — the ultimate source of all genetic variation. (4) Gene flow: movement of alleles between populations by migration — tends to homogenize allele frequencies. (5) Non-random mating: sexual selection, assortative mating, or inbreeding — changes genotype frequencies without necessarily changing allele frequencies.

Natural selection operates when three conditions are met: (1) Variation: individuals vary in traits. (2) Heritability: traits are partly heritable (passed from parent to offspring). (3) Differential fitness: some trait variants increase survival and/or reproduction. Selection types: Directional: one extreme of a trait is favored → population mean shifts (antibiotic resistance evolution). Stabilizing: intermediate trait values favored → reduced variance (birth weight in humans). Disruptive (diversifying): both extremes favored → bimodal distribution → may lead to speciation. Sexual selection: traits that increase mating success are favored, even if they reduce survival (peacock tails, deer antlers) — leads to sexual dimorphism.

Hardy-Weinberg principle: in an ideal population (infinite size, random mating, no selection, no mutation, no gene flow), allele frequencies remain constant and genotype frequencies are: AA = p²; Aa = 2pq; aa = q². A population in HWE is not evolving. Importance: HWE serves as the null model for evolution. Deviation from HWE indicates that at least one evolutionary mechanism is acting. Used to: test for natural selection (excess of certain genotypes); detect population structure (deficit of heterozygotes); estimate carrier frequencies in genetics (2pq for autosomal recessive); identify genotyping errors in GWAS (systematic HWE deviation across all SNPs).

Speciation is the process by which one species splits into two or more reproductively isolated species. Allopatric speciation (most common): a geographic barrier (mountain range, ocean, river) splits a population → the two isolated groups diverge genetically through selection, drift, and mutation → if barriers persist long enough, reproductive isolation develops (prezygotic: different timing, habitat, behavior; postzygotic: hybrids are sterile or inviable). Sympatric speciation: speciation without geographic isolation; occurs through: polyploidy (chromosome doubling in plants — instantaneous speciation); disruptive selection creating reproductive isolation within a population; host shifts in parasites or phytophagous insects. Biological species concept: species = groups that interbreed and produce fertile offspring in nature. Limitations: doesn't apply to asexual organisms; ring species complicate boundaries.