quinta-feira, 18 de novembro de 2010

Self-Organized Criticality and Gaia

In a seminal work, Jim Lovelock, an English scientist, came up with a fascinating idea that all life on earth can be viewed as a single organism. This idea has stuck many scientists as preposterous since it flies in the face of the usual reductionist approach and smacks of New-Age philosophy. Lovelock's idea is that the environment, including the air that we breathe, should not be viewed as an external effect independent of biology, but that it is endogenous to biology. The oxygen represents one way for species to interact. Lovelock
noted that the composition of oxygen has increased dramatically since life originated. The oxygen content is far out of equilibrium. The layer of ozone, an oxygen molecule, that protects life on earth did not just happen to be there, but was formed by the oxygen created by life itself. Therefore, it does not make sense to view the environment, exemplified by the amount of oxygen, as separate from biological life. One should think of the earth as one single system.

What does it mean to say that the earth is one living organism? One might ask in general: What does it mean that anything, such as a human, is one organism? An organism maybe defined as a collection of cells or other entities that are coupled to each other so that they may exist, and cease to exist, at the same time -- that is, they share one another's fate. The definition of what represents an organism depends on the time scale that we set. ln a time scale of 100 million years, all humans represent one organism. At short time scales, an ant's nest is an organism. There is no fundamental difference between genetically identical ants carrying material back and forth to build and operate their nest, and genetically identical human cells organizing themselves in structures and sending blood around in the system to build and operate a human body.

Thus a single organism is a structure in which the various parts are interconnected, or "functionally integrated" so that the failure of one part may cause the rest of the structure to die, too. The sand pile is an organism because sand grains toppling anywhere may cause toppling of grains anywhere in the pile.

One might think of self-organized critically as the general, underlying theory Ear the Gaia hypothesis In the critical state the collection of species represents a single coherent organism following its own evolutionary dynamics. A single triggering event can cause an arbitrarily large fraction of the ecological network to collapse, and eventually be replaced by a new stable ecological network. This would be a "mutated" global organism. At the critical point all species influence each other. ln this state they act collectively as a single meta-organism, many sharing the same fate. This is highlighted by the very existence of large-scale extinctions A meteorite might have directly impacted a small part of the organism, but a large Fraction of the organism eventually died as a result.

Within the SOC picture. the entire ecology has evolved into the critical state. It makes no sense to view the evolution of individual species independently, Atmospheric oxygen might be thought of as the bloodstream connecting the various parts of our Gaia organism, but one can envision organisms that interact in different ways.

The vigorous opposition to the Gaia hypothesis, which represents a genuine holistic view of life, represents the frustration of a science seeking to maintain its reductionist view of biological evolution.

(from: How Nature Works: The Science of Self-Organized Criticality, Per Bak)

Here followa two interesting videos with Lovelock.

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