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Patterns of evolution
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#1. TimingGradualism Punctuated Equilibrium
• Rate of evolution is very slow and constant
• (millions of years)
• Evolution occurs in bursts (thousands of years) followed by millions of years of stasis
**Note in geologic time “short” and “rapid” can mean hundreds of thousands to millions of years! The fossil record shows both of these theories as possibilities.
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More on punctuated Equilibrium
• Evidence that evolution occurs more rapidly following environmental change
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#2 Divergent/Adaptive Radiation
• Species evolve to look different
• Often times many groups evolve from one common ancestor
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Example Darwin’s Finches on the Galapagos Islands: one species from the mainland evolved into many species
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Fall of dinosaurs gave rise to adaptive radiation of mammals
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Interpreting Evolutionary Trees
Fig. 16-11
past
(a) Evolutionary tree (b) Evolutionary tree representingadaptive radiation
In an adaptiveradiation, multiplespeciation eventsmay occur rapidlyenough thatbiologists cannotbe certain of theirorder
present
Forksrepresentspeciationevents
Each linerepresentsa species
time
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#3 Convergent• Different species evolve
to appear similar despite different ancestry = NO RECENT COMMON ANCESTOR
• Leads to formation of analogous structures
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Example – Placental vs.
marsupial mammals
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Example of analogous structures - wings
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III. Coevolution: Process in which two species evolve together in response to change in each other
a. Examples: Orchid and moth, insects and plant poison, hummingbird & flower structure.
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Example – milkweed and Monarch Butterflies
• Milkweed is toxic• Monarch butterflies
feed on milkweed and have evolved to withstand the toxin
• They become toxic to predators
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#4 Aposematic coloration
• Prey evolve very bright coloration
• Predators have evolved to avoid butterflies with bright coloration
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#5 mimicry
• Harmless species evolve to appear similar to toxic/dangerous species
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#6 Developmental Genescalled hox genes:
Developmental genesChanges during the
embryonic stage can have a huge effect.
This lends itself to patterns in morphology: heads, trunk, legs being an example.
http://www.pbs.org/wgbh/evolution/library/03/4/l_034_04.html Hox gene video (~5 min)
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• MACROEVOLUTION practice quiz• HW Quiz next class-allele frequency (not the
math just the concept behind why they shift), causes of microevolution, phylogenic trees, species, patterns of evolution.