COMPLEXITY AS SEEN IN EVOLUTION

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The two main areas that define evolution are extinction and speciation. A central theme of non linear evolutionary theories which contrasts catastrophic theories of extinction and speciation is that ecosystems are deterministic, due to feedback that arises from ecological cross linking. Critical systems which are highly organized (i.e. deterministic) owe their "criticality" to complex, generally non linear interactions between variables. An often used metaphor to desrcribe self-organized criticality was coined by physicist Per Bak. He asked one to consider a tabletop onto which sand is droppped at a uniform rate. As sand piles up, it begins to slide off the edges of the table .
The system eventually reaches a steady rate at which the mean rate of dropping sand onto the pile equals the mean rate at which sand falls off the edges. At this stage, the slopes from the peak to edges of the table, are near the critical resting angle for the sand. Bak asks "if one adds a single grain of sand to the pile, at a random location thereby creating an avalanche, what will the distribution of avalanche sizes be?". He finds a characteristic power law distribution (a typical complexity signature) relating the frequencies & sizes of avalanches with many small ones and few large ones.
He argues that this distribution is characteristic of a wide range of phenomenon, including, earthquakes.



HOW DOES THIS SANDPILE METAPHOR , REPRESENTING SELF - ORGANIZED
CRITICALITY, RELATE TO EXTINCTION AND SPECIATION EVENTS, &
THUS BIOLOGICAL EVOLUTION ???

CLICK HERE TO FIND OUT !!!


Complexity index