biology 145 evolution - claremont colleges
TRANSCRIPT
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Rate of evolutionary change
R = LnX2 –LnX1
Δt
1 Darwin = 2.718/million years
(0.1 D ~ 30% change per million years
Rates of Evolution – mammals ‐ ~ 0.05 – 0.1 Darwins
BUT… bursts of rapid evolution, ~ 10 Darwins.
Red deer, Jersey, ~ 260 Darwins
Evolution under ARTIFICIAL selection can be 100,000 x faster!
Rates of evolution are often INVERSELY correlated with the time interval examined:
Interval length
Rate
GRADUALISM versus PUNCTUATED EQUILIBRIUM
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Punctuated Equilibrium versus Richard Goldschmidts’s “Hopeful monster” theory (1930’s ‐ 1940’s)
“I do, however, predict that during this decade Goldschmidt will be largely vindicated in the world of evolutionary biology.....As a Darwinian, I wish to defend Goldschmidt's postulate that macroevolution is not simply microevolution extrapolated, and that major structural transitions can occur rapidly without a smooth series of intermediate stages. “ S. J. Gould
Lake Turkana, Kenya
Stasis …… punctuated equilibrium?
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Trilobites: gradualism?
Gradualism –many small steps
Punctuated Equilibrium – fewer, larger, steps
Are Gradualism and Punctuated Equilibrium really different?
Rate
TIME
Adaptive radiations
"evolutionary divergence of members of a single phyletic line into a series of rather different niches or adaptive zones“ Mayer.
Ammonites –environmental change
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Adaptive Radiation ‐ Cichlid fishes – “adaptive breakthrough”
Lake Malawi – 785 m deep –4.5 million yrs old –at least 500 spcichlids! Monophyletic!
The cichlid breakthrough –pharyngeal jaws
Adaptive radiations – isolated archipelagoes – habitat breakthrough
Hawaiian Silverswords