COMPLEXITY AS SEEN IN EVOLUTION
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
He argues that this distribution is characteristic of a wide range of phenomenon,
HOW DOES THIS SANDPILE METAPHOR , REPRESENTING
SELF - ORGANIZED
CRITICALITY, RELATE TO EXTINCTION AND SPECIATION EVENTS, &
THUS BIOLOGICAL EVOLUTION ???
CLICK HERE TO FIND OUT !!!