Ev Bio Mt 1 - Vocab Definitions

eidos

The Platonic concept of fixed, idealized forms that dominated pre-Darwinian Western thought.

besoin

Lamarck’s concept of physical "needs" created by environmental shifts that stimulate the acquisition of traits.

plenitude

The assumption that a perfect creator would leave no gaps in nature and permit no extinctions.

catastrophism / uniformitarianism

Early geological frameworks; catastrophism relied on sudden events to explain fossils, while Hutton's uniformitarianism provided a framework for slow, continuous planetary change.

Scala Naturae

The Great Chain of Being linking inanimate matter through plants and animals to angels/God.

Essentialism

The belief that intra-species variations are merely imperfect copies of an ideal form.

Homology vs. Analogy

Homology is similarity due to descent from a common ancestor; Analogy is similarity despite different ancestry, driven by convergent evolution.

Cladogenesis

The splitting of evolutionary lineages where independent mutations accumulate.

Synapomorphies

Shared, derived traits used to map evolutionary relationships.

Parsimony

The principle that the most accurate phylogenetic tree requires the fewest total evolutionary changes or steps.

Molecular clock

Using genetic divergence (percent nucleotide differences) to track evolutionary time.

Exaptations

Traits that originally evolved for one function but were later co-opted for another (e.g., dinosaur feathers for flight).

Monophyletic / Paraphyletic / Polyphyletic groups

Monophyletic

A true clade containing an ancestor and all its descendants.

Paraphyletic

Excludes some descendants (e.g., Reptilia excluding birds).

Polyphyletic

Groups organisms without an exclusive recent common ancestor (e.g., "warm-blooded vertebrates").

Synonymous (silent) vs. Non-synonymous mutations

A 3rd position codon mutation is mathematically 69% likely to be synonymous (invisible to selection); a 2nd position mutation is 100% likely to be non-synonymous (alters the amino acid).

Central Dogma

The unidirectional flow of information

Germline vs. Soma

Weismann’s doctrine separating reproductive cells (germline) from body cells (soma), proving somatic mutations cannot be inherited.

Transitions vs. Transversions

Transitions are purine-to-purine or pyrimidine-to-pyrimidine swaps; Transversions are cross-category purine-to-pyrimidine swaps.

Single Nucleotide Polymorphisms (SNPs) & Haplotypes

SNPs are single variable nucleotides (~1 every 1000 bp in humans); a haplotype is a set of linked SNPs along a single chromosome.

Pleiotropy vs. Epistasis

Pleiotropy is one mutation causing multiple phenotypic effects; Epistasis is the expression of one locus being modified by the genotype of a separate interacting locus.

Canalized vs. Plastic

Genotypes with no response to environmental changes are canalized; sensitive genotypes are plastic.

Genotype-by-Environment (GxE) interaction

When different genotypes respond to the same environmental shift in fundamentally different, non-parallel ways.

Directional / Stabilizing / Disruptive Selection

Directional

Favors phenotypic extremes.

Stabilizing

Favors intermediates.

Disruptive

Favors both extremes over intermediates.

Overdominance (Heterosis)

Balancing selection where heterozygotes exhibit fitness superior to either homozygote.

Marginal Overdominance

A mathematical state where the heterozygote may not be the fittest in any single niche, but its weighted average fitness across all available niches outperforms both homozygotes.

Multiple Niche Polymorphism

Different habitats favoring different genotypes across a landscape.

Linkage disequilibrium (D)

The non-random association of linked alleles.

Coupling gametes (AB, ab)

push D toward 0.25.

Repulsion gametes (Ab, aB)

push D toward -0.25.

Genetic hitchhiking

Neutral/deleterious variants physically linked to a favored variant are dragged to high frequency during a selective sweep.

Supergenes

Tightly linked clusters of interacting loci with highly favorable allelic combinations that behave as a single genetic unit due to suppressed recombination.

Founder Effect

A specific subset of genetic drift where sampling error occurs upon the geographic establishment of a new, tiny population.

Natural Selection

The true driving force of evolution identified by Darwin and Wallace, where heritable intra-species variation results in differential survivorship and reproductive success.

The Modern Synthesis

Developed in the 1920s by R.A. Fisher, Sewall Wright, and J.B.S. Haldane to unite Darwinian selection with particulate Mendelian factors, solving the fatal mathematical flaw of "blending inheritance."

The Law of Succession

Extant organisms strongly resemble extinct fossil forms found in the identical geographic region.

The Classical vs. Balance Debate (Neutralist-Selectionist)

Classical School (H.J. Muller)

Populations harbor low variation because purifying selection aggressively eliminates mutants to favor a "wild type."

Balance School (T. Dobzhansky)

High variation is actively maintained via balancing selection and heterozygote advantage.