Evolution, Speciation, and History of Life — Key Terms

Vocabulary flashcards covering key concepts, terms, and definitions from Darwinian evolution, speciation, and the history of life.

Evolution

The process by which heritable changes accumulate in a population over time, leading to descent with modification.

Fixity of Species

The belief that species are unchanging and individually created, common in the Middle Ages.

Essential form (Plato)

Idea that each species has an immutable, perfect form or essence.

Great Chain of Being (Aristotle)

A hierarchical view of life organized from simple to complex, with all species fixed in rank.

Constant transformation (Zhuang Zhou)

Philosophical idea that species undergo continual change in response to environments.

Buffon’s struggle for existence

Early evidence for evolution and competition, though Buffon remained uncertain about full evolution.

Linnaeus & taxonomy

Father of modern taxonomy who created hierarchical classification but believed in fixity of species.

Lamarckian Transformism

Idea of descent with modification through inheritance of acquired characteristics; first to outline a process for evolution.

Inheritance of Acquired Characteristics

Lamarck’s proposed mechanism by which traits acquired during life could be passed to offspring.

Catastrophism

Cuvier’s view that global catastrophes caused mass extinctions and subsequent repopulation explains fossil changes.

Uniformitarianism

Geological principle that slow, gradual processes shape Earth over long timescales.

Deep Time

The concept that Earth is very old, allowing enough time for evolutionary processes.

Malthusian Struggle for Existence

Idea that populations grow faster than resources, leading to competition and natural selection.

Natural Selection

Process where heritable variation leads to differential survival and reproduction, changing populations over time.

Variation

Heritable differences among individuals; the raw material for evolution.

Fitness (Darwinian)

An individual’s ability to survive and reproduce relative to others in the population.

Adaptive Radiation

Rapid diversification of a lineage into multiple ecologically distinct species.

Biogeography

Study of the geographic distribution of species and their evolutionary history.

Common Ancestry

Idea that related species share a common ancestor.

Descent with Modification

Darwin’s concept that species accumulate differences from their ancestors over time.

Darwin & Wallace (1858)

Two scientists who independently conceived natural selection; their ideas were presented jointly.

Four Observations of Natural Selection

Variation is heritable; organisms compete for resources; differential survival/reproduction; successful traits become more common.

Heritable Variation

Genetic variation that can be passed to offspring and fuel evolution.

Mutation (source of variation)

A heritable change in DNA that creates new genetic variation.

Biogeography & Adaptive Radiation (Galapagos)</definition

Geographic isolation and different environments drive diversification of related species.

Homologous Traits

Similar anatomical structures in different species from common ancestry.

Analogous Traits

Similar functions in different lineages due to convergent evolution, not common ancestry.

Vestigial Structures

Remnants of features that were functional in ancestors but are reduced or unused in present species.

Embryo Development Patterns

Similarities among vertebrate embryos suggesting common ancestry.

Biochemical Evidence of Evolution

All life shares fundamental biomolecules and a nearly universal genetic code, revealing relatedness.

Microevolution

Change in allele frequencies within a population over time.

Population

Group of interbreeding individuals of the same species in a specific area.

Gene Pool

Total collection of alleles and gametes in a population.

Allele Frequency (p and q)

Proportions of dominant (p) and recessive (q) alleles in a population, with p + q = 1.

Hardy-Weinberg Principle

Null model predicting constant allele and genotype frequencies in the absence of evolutionary forces.

Genotype Frequencies (p^2, 2pq, q^2)

Expected frequencies of AA, Aa, and aa genotypes under Hardy-Weinberg equilibrium.

Assumptions of Hardy-Weinberg

Large population, no gene flow, no mutation, no natural selection, random mating.

Mutation (as an evolutionary force)

Introduces new genetic variation; rates are typically low but essential for evolution.

Gene Flow (Migration)

Movement of alleles between populations that tends to homogenize gene pools.

Genetic Drift

Random fluctuations in allele frequencies due to chance, stronger in small populations.

Genetic Bottleneck

Severe reduction in population size causing loss of genetic variation due to drift.

Founder Effect

Genetic drift when a new population is started by a small number of individuals, reducing variation.

Inbreeding Depression

Increase in deleterious alleles due to mating among related individuals in small populations.

Non-Random Mating

Mating that is not random, affecting genotype frequencies and potentially aiding selection.

Natural Selection (as an evolutionary force)

The only force that leads to adaptation by differential survival and reproduction.

Speciation

The process by which new species arise through evolutionary mechanisms over time.

Biological Species Concept (Mayr)

Species are groups of actually or potentially interbreeding populations that are reproductively isolated.

Morphological Species Concept

Species defined by morphological similarities; useful for fossils and data-poor taxa.

Evolutionary Species Concept

Species defined by abrupt trait changes along an evolutionary pathway.

Phylogenetic Species Concept

Smallest monophyletic group defined by diagnostic traits from a single common ancestor.

Reproductive Isolating Mechanisms

Barriers to gene flow that prevent interbreeding between species.

Prezygotic Barriers

Barriers that prevent zygote formation: temporal, habitat, behavioral, structural, or gametic isolation.

Postzygotic Barriers

Barriers that reduce fitness of hybrids: inviability, sterility, or breakdown.

Reinforcement

Strengthening of prezygotic barriers when hybrids have low fitness in contact zones.

Allopatric Speciation

Speciation due to geographic isolation leading to genetic divergence.

Sympatric Speciation

Speciation without geographic isolation, often via strong selection or polyploidy in plants.

Apple Maggot Fly Example

Diversification driven by host fruit preference causing temporal isolation.

Niche

An organism’s role and position within its ecosystem, including habitat and interactions.

Convergent Evolution

Independent evolution of similar traits in unrelated lineages due to similar pressures.

Evolution is Not Goal-Oriented

Evolution does not progress toward a perfection; it is driven by selection on existing variation.

LUCA (Last Universal Common Ancestor)

The presumed most recent common ancestor of all current life on Earth.

Origin of Life Stages

Abiotic synthesis, polymer formation, protocell formation, and emergence of self-replicating cells.

Oparin-Haldane Primordial Soup

Hypothesis that organic molecules formed spontaneously in early Earth’s oceans.

Reducing Atmosphere Hypothesis

Early Earth atmosphere facilitated synthesis of organic molecules; Miller-Urey experiment supported it.

Panspermia

Hypothesis that organic molecules or life came to Earth from space.

Protocells/Protobionts

Membrane-bound aggregates of prebiotic molecules that prefigure cells.

RNA World Hypothesis

Idea that RNA served as the first genetic material and catalyst before DNA.

Four Eons of Geologic Time

Hadean, Archean, Proterozoic, Phanerozoic—major divisions of Earth’s history.

Fossil Record & Dating

Evidence of past life; relative dating places fossils in strata; radiometric dating uses radioactive decay.

Prokaryotic Stromatolites

Early multicellular fossil records dating 3.8–3.5 billion years ago.

Autotrophs & Oxygen Rise

Oxygen-producing cyanobacteria increased atmospheric O2, shaping later evolution.

Endosymbiosis (Mitochondria & Chloroplasts)

Theory that eukaryotic organelles originated from symbiotic prokaryotes.

Multicellular Eukaryotes & Land Rise

Emergence of complex life and plants/animals expanding onto land in the Phanerozoic.