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The origins of life
The Punctuated Equilibrium Model
Originally proposed by Stephen Jay Gould and Niles Eldredge (1972).
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 with occasional rapid formation of new species (as little as 5,000 - 50,000 years).
During stasis the species resists evolutionary change. Gould and Eldredge suggest that a species would move to a new area where it can find its habitat than adapt to a new one. They call this developmental homeostasis. If a small population of a species should get isolated in an area where its habitat does not exist then a rapid change takes place to bring the population back to equilibrium (stasis). But it is no longer the same species.
This could also occur on a global scale if there was a sufficiently large catastrophe.
Four mechanisms have been proposed for punctuated equilibrium pattern of speciation:
What is a species?
The definition of a species from fossils alone is not easy. Though the fossil remains (e.g. bones, teeth or shells) may indicate no change during period of stasis there may be significant changes in soft tissues or biochemistry.
How rapid is rapid?
Even though punctuated equilibrium requires rapid change, this does not mean instantaneous. If a species has a minimum duration of 4 million years and the rapid evolution of this theory represents 1% of this time. That means macroevolution of a new species could occur in as little as 40 000 years. Is this a short time?
The incomplete fossil record
Because the changes proposed by punctuated equilibrium are so rapid (on a geological scale), and the fossil record is not complete the transition from one species to another is often missing. Most of the evidence comes from recent geological periods where the fossil record is more complete.
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