With the process of evolution all organisms have developed from an earlier set of ancestors. Adaptive radiation is the process whereby one organism can give rise to many different new forms. A primitive organism can leave offspring all of which are of a similar type which then adapt and evolve slightly differently due to the different pressures that they are placed under from different habitats. For example, it is thought that at the start of the tertiary period there existed a type of relatively undifferentiated, simple mammal. All forms of subsequent mammals,--both living and extinct--have evolved from this common ancestor. The different forms of mammal that have existed are produced because of the different environments that they have evolved to fit.

The classic example of adaptive radiation that can be easily followed and understood is on the Galapagos Islands. These islands were produced by volcanic...