Extinction

Types of Extinction

Extinction events can generally be divided into two types: background extinction and catastrophic, or mass, extinction. Background extinction follows the concept of Darwin's “survival of the fittest,” perhaps better expressed as “survival of the luckiest.” For one reason or another, groups of living organisms regularly pass into oblivion. These reasons include lack of nutrients, disease, genetic anomalies, unusual weather conditions, and being out-competed for existing resources. Changes in climate seem to play the largest role in this type of extinction. Very minor changes, as small as having a drought in a region for a few years, can cause an extinction event.

[Page 937]Background extinction seems to be part of a cycle most species of organisms follow. Initially, a species comes into existence from organisms occupying a new environment or following a new life style compared with their ancestors'. These organisms typically exhibit few specializations, and they are generally not very well suited to the new environment or lifestyle. Through successive generations, the organisms become more specialized and better able to exist in the new environment, but this comes at the cost of being less able to cope with changes to the new environment. Finally, the organism faces the problem of a change in its new environment, and because it no longer has the ability to adapt and change rapidly, it dies out. If the species is not an evolutionary dead end, somewhere in this process, some of the offspring were either born defective, forcing them to move into a different environment to survive, or perhaps a small group was merely trapped in an area where the environment was somewhat different. In any case, the demise of the parent species leaves behind one or more daughter species, and the cycle continues. Throughout the history of the Earth, this pattern has produced a gradual increase in both the number of different species and the complexity of organisms on Earth.

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