Patterns and Processes of Evolution

Macroevolutionary Patterns Large-scale (more than a single species) Occurs over long periods of time

Microevolution Small-scale (within a single species) Forms variations in populations

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Speciation – Isolating MechanismSpecies – group of organisms that interbreed to

produce fertile offspring under normal conditions –

share a common gene poolSpeciation – formation of a new species

Requires reproductive isolation – organisms do not interbreed; gene pools become separateBehavioralGeographicTemporal

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Patterns of Extinction

Background Extinction – “business as usual” extinction – slow and steady

Mass Extinction – many species become extinct over a short period of timeCauses:AsteroidVolcanic eruptionsMoving continentsChanging sea levels

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Rates of Evolution

Gradualism – change in species is slow and steady

Punctuated Equilibrium – long periods of stability followed by short periods of rapid change

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Patterns of Macroevolution:

Adaptive RadiationA single species evolves into many speciesOften occurs when a niche opens up

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Organisms come to resemble one another but evolved differently

Source of analogous structures!

Examples: Dolphins and sharks Marsupials and

mammals

Patterns of Macroevolution:

Convergent Evolution

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Coevolution

Organisms with close ecological relationships evolve togetherPollinators and flowers

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The Role of Genes in Evolution

In terms of genetics, evolution is the change in the frequency of alleles in a population’s gene pool

Natural selection leads to that change

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Genetic DriftRandom change in allele frequency –

changes in the gene pool of a small population due to chance

Types of Genetic Drift: Bottleneck Effect – change in allele

frequency following dramatic reduction in population size

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Genetic Drift Founder Effect – small group colonizes a

new habitat

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Molecular Evolution

Molecular Clocks – use mutation rates in DNA to estimate time two species have been evolving independently

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Molecular Evolution: Hox Genes

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Genes which control an organism’s basic body plan Anterior/posterior ends Limbs, wings

small sequence changes during embryological development can cause large changes in adults