The theory of evolution by natural selection (Darwin & Wallace, 1858). Key components: individuals in a population vary; some variations are heritable; more offspring are produced than can survive (struggle for existence); individuals with favorable variations survive and reproduce (survival of the fittest); favorable traits become more common over generations (descent with modification)
The number of viable offspring an individual contributes to the next generation. "Fitness" in evolutionary biology = reproductive success, not physical strength. An individual can be "fit" by reproducing more or by helping relatives reproduce (kin selection, inclusive fitness - Hamilton's rule: rB > C). Fitness is relative to the environment and other individuals in the population
The environmental force that drives natural selection. Can be biotic (predation, competition, disease) or abiotic (temperature, moisture, pH). Stronger selection pressure -> faster evolutionary change. Different selection pressures in different environments -> different traits -> speciation over time
A form of natural selection based on mate choice. Intrasexual selection: members of one sex compete for mates (e.g., male deer antlers, elephant seals fighting). Intersexual selection: members of one sex choose mates based on traits (e.g., peacock tail, bird song). Secondary sexual characteristics evolve because they increase mating success, even if they reduce survival. Runs counter to natural selection in some cases
Humans intentionally breed organisms with desired traits over generations. The principle is the same as natural selection but humans choose the mates. Examples: dog breeds, crop plants (corn from teosinte), livestock. Demonstrates that heritable variation exists and that selection can produce dramatic change over time. Contrasted with natural selection
Random changes in allele frequencies due to chance events, not selection. Most significant in small populations. Two major examples: bottleneck effect and founder effect. Does not lead to adaptation - can reduce fitness. Particularly important in endangered species, island populations, newly founded colonies
A dramatic reduction in population size (due to natural disaster, habitat loss, overhunting) that causes a loss of genetic diversity. The surviving population has a reduced gene pool. Even if the population recovers, it has less genetic variation. Example: cheetahs (genetic bottleneck ~10,000 years ago) -> very low genetic diversity today
A small group breaks off from a larger population to found a new colony. The founders carry only a subset of the original population's genetic diversity. The new population may have very different allele frequencies. Example: Amish population (founder effect for Ellis-van Creveld syndrome). Both bottleneck and founder effect are special cases of genetic drift
The movement of alleles between populations via migration. Reduces genetic differences between populations. Introduces new alleles into populations. Can counteract the effects of drift and natural selection. Example: pollen dispersal, animal migration, human migration. Gene flow between species (hybridization) can create new species
Hardy-Weinberg equilibrium holds when: (1) No mutations (no new alleles arise); (2) Random mating (no sexual selection); (3) Large population (no genetic drift); (4) No natural selection (all genotypes have equal survival); (5) No gene flow (no migration). When these conditions are met, allele frequencies do not change -> no evolution occurring
If p = frequency of dominant allele (A) and q = frequency of recessive allele (a): p + q = 1. Allele frequency can be calculated from genotype frequency: p = (2×AA + Aa) / (2× total individuals). If p = 0.8, q = 0.2. When p or q = 0 or 1, one allele has been lost
The collection of fossils preserved in rock layers. Shows a chronological sequence of life forms over ~3.5 billion years. Demonstrates that life forms have changed over time. Transitional forms (e.g., Archaeopteryx: reptile-bird) show evolutionary connections. The geological timescale is established using radiometric dating. Gaps exist due to incomplete fossilization and rock destruction
Structures in different species that share a common ancestral origin but may have different functions. Evidence for common ancestry. Examples: forelimbs of humans, bats, whales, cats (all modified from the same ancestral limb bones: humerus, radius, ulna, carpals, metacarpals, phalanges). Vestigial structures are homologous to functional structures in other species
Remnants of structures that were functional in ancestral species but are now reduced or non-functional. Evidence for evolution - the structure had a function that was lost over time. Examples: human appendix, whale hip bones, blind cave fish eyes, wings in flightless birds. Not evidence of "imperfect design" but of evolutionary change
DNA and protein sequence comparisons provide powerful evidence for evolution. Related species have more similar sequences. The number of sequence differences is proportional to the time since divergence. Examples: cytochrome c (all eukaryotes share this protein), rRNA sequences used to build the tree of life, mitochondrial DNA to track human migrations. Universal genetic code supports common ancestry
All life shares a common ancestor (Last Universal Common Ancestor, LUCA). Evidence: universal genetic code, common biochemistry (ATP, DNA, RNA, proteins), homologous structures, molecular sequences. The tree of life branches from this common origin. All organisms are relatives - we share ancestry with bacteria, plants, and all other living things
Evolution is an ongoing process. Species continue to adapt to changing environments. Observable evolution: antibiotic resistance in bacteria, pesticide resistance in insects, climate-driven range shifts, beak size changes in Galápagos finches (Grant's research). Evolution does not stop; it continues as environments change
A branching diagram showing the evolutionary history and relationships among species. Each branch point (node) represents a common ancestor. The length of branches may represent time or the number of changes. Root = most recent common ancestor of all taxa shown. Tips = extant species. Clades = groups sharing a common ancestor
A type of phylogenetic tree that groups organisms by shared derived characteristics (synapomorphies). Closely related organisms share more derived characters. The branching pattern shows the order in which derived characters evolved. Cladistics: the method of classifying organisms based on evolutionary relationships (cladistics). Outgroup comparison used to root the tree
A species or group known to be distantly related to all members of the ingroup. Used to root phylogenetic trees. Outgroup comparison identifies which character states are ancestral (plesiomorphies) vs. derived (apomorphies). Example: lamprey as an outgroup to jawed vertebrates. Essential for determining the direction of character evolution
Speciation that occurs when a geographic barrier separates a population. Examples: mountain ranges, oceans, glaciers. The separated populations evolve independently (allopatric evolution). Over time, genetic differences accumulate -> reproductive isolation. If the barrier is removed, they may not be able to interbreed -> two species. Very common mode of speciation
Speciation without geographic separation. Occurs within a single population. Mechanisms: polyploidy in plants (most common), sexual selection (mate preference divergence), ecological niche differentiation. More controversial than allopatric speciation. Examples: cichlid fish in African lakes, apple maggot flies on hawthorn vs. apple
Reproductive isolation mechanisms that prevent fertilization and zygote formation. Five types: (1) Habitat isolation (different environments), (2) Temporal isolation (different breeding times), (3) Behavioral isolation (different mating rituals), (4) Mechanical isolation (incompatible reproductive structures), (5) Gametic isolation (sperm and egg incompatible)
Reproductive isolation mechanisms that act after fertilization, reducing hybrid viability or fertility. Three types: (1) Hybrid inviability (zygote fails to develop), (2) Hybrid sterility (F1 generation is sterile, e.g., mule), (3) Hybrid breakdown (F2 generation is weak or sterile). These are "last resort" barriers - the energy cost is higher
Events where a large proportion of Earth's species go extinct in a geologically short time. Five major mass extinctions: Ordovician, Devonian, Permian ("The Great Dying," ~90% of marine species), Triassic, Cretaceous (dinosaurs). Currently in a 6th mass extinction driven by human activity. Mass extinctions create ecological opportunities for surviving lineages -> adaptive radiation
Genetic variation that has no effect on fitness. Most DNA mutations are neutral. Does not affect survival or reproduction -> not acted upon by natural selection. Accumulates by genetic drift. Provides the raw material for evolution - if the environment changes, previously neutral variation may become advantageous
Classic experiment (1953, Stanley Miller & Harold Urey) testing the hypothesis that Earth's early atmosphere (CH4, NH3, H2, H2O) + lightning (energy) could produce organic molecules. Result: amino acids and other organic compounds formed in a week. Demonstrated that prebiotic synthesis of life's building blocks is possible
The hypothesis that RNA was the first genetic material and catalyst on early Earth. RNA can: (1) store genetic information (like DNA), (2) catalyze chemical reactions (like proteins/enzymes - ribozymes). RNA world -> DNA and proteins evolved later. Supported by: ribosomes are made primarily of RNA, RNA can catalyze reactions, self-replicating RNA has been created in labs
The theory of evolution by natural selection (Darwin & Wallace, 1858). Key components: individuals in a population vary; some variations are heritable; more offspring are produced than can survive (struggle for existence); individuals with favorable variations survive and reproduce (survival of the fittest); favorable traits become more common over generations (descent with modification)
The number of viable offspring an individual contributes to the next generation. "Fitness" in evolutionary biology = reproductive success, not physical strength. An individual can be "fit" by reproducing more or by helping relatives reproduce (kin selection, inclusive fitness - Hamilton's rule: rB > C). Fitness is relative to the environment and other individuals in the population
The environmental force that drives natural selection. Can be biotic (predation, competition, disease) or abiotic (temperature, moisture, pH). Stronger selection pressure -> faster evolutionary change. Different selection pressures in different environments -> different traits -> speciation over time
A form of natural selection based on mate choice. Intrasexual selection: members of one sex compete for mates (e.g., male deer antlers, elephant seals fighting). Intersexual selection: members of one sex choose mates based on traits (e.g., peacock tail, bird song). Secondary sexual characteristics evolve because they increase mating success, even if they reduce survival. Runs counter to natural selection in some cases
Humans intentionally breed organisms with desired traits over generations. The principle is the same as natural selection but humans choose the mates. Examples: dog breeds, crop plants (corn from teosinte), livestock. Demonstrates that heritable variation exists and that selection can produce dramatic change over time. Contrasted with natural selection
Random changes in allele frequencies due to chance events, not selection. Most significant in small populations. Two major examples: bottleneck effect and founder effect. Does not lead to adaptation - can reduce fitness. Particularly important in endangered species, island populations, newly founded colonies
A dramatic reduction in population size (due to natural disaster, habitat loss, overhunting) that causes a loss of genetic diversity. The surviving population has a reduced gene pool. Even if the population recovers, it has less genetic variation. Example: cheetahs (genetic bottleneck ~10,000 years ago) -> very low genetic diversity today
A small group breaks off from a larger population to found a new colony. The founders carry only a subset of the original population's genetic diversity. The new population may have very different allele frequencies. Example: Amish population (founder effect for Ellis-van Creveld syndrome). Both bottleneck and founder effect are special cases of genetic drift
The movement of alleles between populations via migration. Reduces genetic differences between populations. Introduces new alleles into populations. Can counteract the effects of drift and natural selection. Example: pollen dispersal, animal migration, human migration. Gene flow between species (hybridization) can create new species
Hardy-Weinberg equilibrium holds when: (1) No mutations (no new alleles arise); (2) Random mating (no sexual selection); (3) Large population (no genetic drift); (4) No natural selection (all genotypes have equal survival); (5) No gene flow (no migration). When these conditions are met, allele frequencies do not change -> no evolution occurring
If p = frequency of dominant allele (A) and q = frequency of recessive allele (a): p + q = 1. Allele frequency can be calculated from genotype frequency: p = (2×AA + Aa) / (2× total individuals). If p = 0.8, q = 0.2. When p or q = 0 or 1, one allele has been lost
The collection of fossils preserved in rock layers. Shows a chronological sequence of life forms over ~3.5 billion years. Demonstrates that life forms have changed over time. Transitional forms (e.g., Archaeopteryx: reptile-bird) show evolutionary connections. The geological timescale is established using radiometric dating. Gaps exist due to incomplete fossilization and rock destruction
Structures in different species that share a common ancestral origin but may have different functions. Evidence for common ancestry. Examples: forelimbs of humans, bats, whales, cats (all modified from the same ancestral limb bones: humerus, radius, ulna, carpals, metacarpals, phalanges). Vestigial structures are homologous to functional structures in other species
Remnants of structures that were functional in ancestral species but are now reduced or non-functional. Evidence for evolution - the structure had a function that was lost over time. Examples: human appendix, whale hip bones, blind cave fish eyes, wings in flightless birds. Not evidence of "imperfect design" but of evolutionary change
DNA and protein sequence comparisons provide powerful evidence for evolution. Related species have more similar sequences. The number of sequence differences is proportional to the time since divergence. Examples: cytochrome c (all eukaryotes share this protein), rRNA sequences used to build the tree of life, mitochondrial DNA to track human migrations. Universal genetic code supports common ancestry
All life shares a common ancestor (Last Universal Common Ancestor, LUCA). Evidence: universal genetic code, common biochemistry (ATP, DNA, RNA, proteins), homologous structures, molecular sequences. The tree of life branches from this common origin. All organisms are relatives - we share ancestry with bacteria, plants, and all other living things
Evolution is an ongoing process. Species continue to adapt to changing environments. Observable evolution: antibiotic resistance in bacteria, pesticide resistance in insects, climate-driven range shifts, beak size changes in Galápagos finches (Grant's research). Evolution does not stop; it continues as environments change
A branching diagram showing the evolutionary history and relationships among species. Each branch point (node) represents a common ancestor. The length of branches may represent time or the number of changes. Root = most recent common ancestor of all taxa shown. Tips = extant species. Clades = groups sharing a common ancestor
A type of phylogenetic tree that groups organisms by shared derived characteristics (synapomorphies). Closely related organisms share more derived characters. The branching pattern shows the order in which derived characters evolved. Cladistics: the method of classifying organisms based on evolutionary relationships (cladistics). Outgroup comparison used to root the tree
A species or group known to be distantly related to all members of the ingroup. Used to root phylogenetic trees. Outgroup comparison identifies which character states are ancestral (plesiomorphies) vs. derived (apomorphies). Example: lamprey as an outgroup to jawed vertebrates. Essential for determining the direction of character evolution
Speciation that occurs when a geographic barrier separates a population. Examples: mountain ranges, oceans, glaciers. The separated populations evolve independently (allopatric evolution). Over time, genetic differences accumulate -> reproductive isolation. If the barrier is removed, they may not be able to interbreed -> two species. Very common mode of speciation
Speciation without geographic separation. Occurs within a single population. Mechanisms: polyploidy in plants (most common), sexual selection (mate preference divergence), ecological niche differentiation. More controversial than allopatric speciation. Examples: cichlid fish in African lakes, apple maggot flies on hawthorn vs. apple
Reproductive isolation mechanisms that prevent fertilization and zygote formation. Five types: (1) Habitat isolation (different environments), (2) Temporal isolation (different breeding times), (3) Behavioral isolation (different mating rituals), (4) Mechanical isolation (incompatible reproductive structures), (5) Gametic isolation (sperm and egg incompatible)
Reproductive isolation mechanisms that act after fertilization, reducing hybrid viability or fertility. Three types: (1) Hybrid inviability (zygote fails to develop), (2) Hybrid sterility (F1 generation is sterile, e.g., mule), (3) Hybrid breakdown (F2 generation is weak or sterile). These are "last resort" barriers - the energy cost is higher
Events where a large proportion of Earth's species go extinct in a geologically short time. Five major mass extinctions: Ordovician, Devonian, Permian ("The Great Dying," ~90% of marine species), Triassic, Cretaceous (dinosaurs). Currently in a 6th mass extinction driven by human activity. Mass extinctions create ecological opportunities for surviving lineages -> adaptive radiation
Genetic variation that has no effect on fitness. Most DNA mutations are neutral. Does not affect survival or reproduction -> not acted upon by natural selection. Accumulates by genetic drift. Provides the raw material for evolution - if the environment changes, previously neutral variation may become advantageous
Classic experiment (1953, Stanley Miller & Harold Urey) testing the hypothesis that Earth's early atmosphere (CH4, NH3, H2, H2O) + lightning (energy) could produce organic molecules. Result: amino acids and other organic compounds formed in a week. Demonstrated that prebiotic synthesis of life's building blocks is possible
The hypothesis that RNA was the first genetic material and catalyst on early Earth. RNA can: (1) store genetic information (like DNA), (2) catalyze chemical reactions (like proteins/enzymes - ribozymes). RNA world -> DNA and proteins evolved later. Supported by: ribosomes are made primarily of RNA, RNA can catalyze reactions, self-replicating RNA has been created in labs