Associate extinction of a species with environmental changes and insufficient adaptive characteristics. Evolutionary theory holds that the presence of life itself and today's biodiversity were the result of these processes. Darwinian evolutionary theory can generally be separated into microevolution and macroevolution. These processes may produce speciation, the splitting off of new reproductively isolated species. Microevolution is also evidenced by plant and animal breeders as they change the outward appearance or behavior of members of a population of a species by selective breeding.
Macroevolution is a theoretical extrapolation of microevolution over very long time periods.
The sources and value of variation. Variation of organisms within and among species increases the likelihood that some members will survive under changed environmental conditions. The theory postulates that evolution modifies what exists and that evolution does not necessitate long-term progress in some set direction. According to the theory, the more variation in a species, the greater its adaptive potential. Some biologists believe that natural selection and random genetic drift are not competent to produce information systems or the processed information that distinguishes living from non living systems.