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PUNCTUATED EQUILIBRIUM

PUNCTUATED EQUILIBRIUM. NEO-DARWINISM. Evolutionary change is both slow and gradual Resulting from the accumulation of many small genetic changes favoured by natural selection Other effects occasionally making small contributions Gradualism. © 2008 Paul Billiet ODWS.

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PUNCTUATED EQUILIBRIUM

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  1. PUNCTUATED EQUILIBRIUM

  2. NEO-DARWINISM • Evolutionary change is both slow and gradual • Resulting from the accumulation of many small genetic changes favoured by natural selection • Other effects occasionally making small contributions • Gradualism © 2008 Paul Billiet ODWS

  3. Evolution of new species • Two possible ways from gradualism • PHYLETIC TRANSFORMATION • ALLOPATRIC SPECIATION © 2008 Paul Billiet ODWS

  4. PHYLETIC TRANSFORMATION • Gradual accumulation of small genetic variations preserved by natural selection • A whole population imperceptibly to evolve in to a new species • Impossible to draw a clear line between the end of the first species and the beginning of its descendant species • There would be a long period of intermediate forms © 2008 Paul Billiet ODWS

  5. ALLOPATRIC SPECIATION • Geographical or reproductive isolation of a part of the population would allow it to evolve in a different direction • Possibly more rapidly than the main population • If the isolated population is small, it might be very difficult to find fossils of the intermediate stages © 2008 Paul Billiet ODWS

  6. Allopatric speciation of Species W into species X due to the isolation of a small population of Species W Allopatric speciation of species Y into species Z due to the isolation of a small population of species Y Time Evolution Species Z Species Y Species X Species Y Phyletic transition of species W into Species Y due to the slow gradual accumulation of mutations in Species W Species W © 2008 Paul Billiet ODWS

  7. Stephen J Gould Niles Eldredge THE PUNCTUATED EQUILIBRIUM MODEL • They observed that the fossil record gives a different picture for the evolution • They claim that there were long periods of stasis (4-10 million years) involving little evolutionary change • Then occasional rapid formation of new species • As little as 5,000 - 50,000 years © 2008 Paul Billiet ODWS

  8. Stasis and change • A species resists evolutionary change • A species would rather move to a new area where it can find its habitat than adapt to a new one • If a small population of a species should get isolated in an area where its habitat does not exist… • …rapid change could take place to bring the population back to equilibrium (stasis) • But it is no longer the same species © 2008 Paul Billiet ODWS

  9. Species Z Species Y Species X Species W Stasis Rapid speciation Rapid speciation Stasis Time Rapid speciation Stasis Evolution © 2008 Paul Billiet ODWS

  10. Mechanisms • Rapid natural selection in isolated populations • Genetic drift in small isolated populations. • Hopeful monsters • Breakdown of developmental homeostasis © 2008 Paul Billiet ODWS

  11. Criticisms • What is a species? • How rapid is rapid? • The incomplete fossil record © 2008 Paul Billiet ODWS

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