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• Defined: evolution of a new
• Species: group of organisms
that can interbreed and
produce fertile offspring
• Isolation reduces gene flow
– Reproductive
– Geographical
– Behavioral
– Temporal
• Gene pools & frequencies
Gene Flow
• Defined: Movement of alleles from 1 population to
• Increases variation
• Keeps differing populations similar
• If gene flow prevented:
– No variations exchanged
– Populations isolated
– Organisms adapt to their own environment
Genetic Drift
• Defined: Changes in gene pool due to chance (not natural
• Bottleneck effect, founder effect
• More likely in smaller populations
• Ex: Forest fire destroys 90% of a forest
– Survival unrelated to adaptations
– Pre-forest fire (left picture): Blue is more advantageous
– Post-forest fire (right picture): Due to more red survivors, red has the
advantage to reproduce in this new environment
Founder Effect: 14 Species of
Galapagos Finches
1) Geographic Isolation
• Mountains, rivers, canyons, oceans may
separate a population
• Each population adapts to its isolated
environment (natural selection)
• Because isolated, no gene flow
2) Behavioral Isolation
• Although not geographically separated,
reproduction is prevented
– 1) Different mating rituals
– 2) Use of pheromones
• No gene flow: differing populations unable to
3) Temporal Isolation
• Although not
separated, reproduction
is prevented
– 1) Mate at different
– 2) Some nocturnal
• No gene flow: differing
populations unable to
End Result: Reproductive Isolation
• Created as a result of
behavioral, geographical,
& temporal isolation
• No mating between
populations (no gene flow)
• Two groups unable to
– Sex organs don’t
match, rituals don’t
attract, physically
• Final step to becoming
different species
• Ultimately leads to
Quick Review
• New species are
created (speciation)
when populations
become isolated
• A changing or new
environment greatly
affects natural