Evolution In Brief (Part 3)

Evolution is a pretty simple concept. There are two main categories of change in genetics, they are macroevolution and microevolution. The two are quite different and when evolution is addressed it is usually macroevolution being discussed. Macroevolution is the change species take over a long period of time (millions of years) to develop into new taxonomic groups. Microevolution are changes that occur within a gene pool from one generation to the next.

One of the driving factors of microevolution is natural selection which effects a change in the gene pool due to the survivability of the fittest individuals. If a particular bear is better able to hunt due to its genetic superiority to the other bears in the immediate area it is more likely to survive and reproduce, by so changing the gene pool and populating subsequent generations with its own genes. Genetic drift are changes in the gene pool due to chance. Gene flow affects microevolution by the movement of individuals who are more likely to reproduce. As America was being shaped many different peoples populated her lands. Many people were introduced to each other who would not otherwise have been able to meet and as a result the gene pool changed. Gene flow reduced the differences between the different ethnic groups by blending them together. Bottlenecking, the founder effect and gene mutation cause microevolution, but not nearly to the degree that natural selection, genetic drift and gene flow do. When it is said that evolution is observable in the span of a life time, this is what is being discussed, and it is far different than macroevolution.

Speciation is the development of new species through the process of evolution. Gene flow stops during speciation and two formerly similar populations drift apart. After a period of time they have drifted so far apart they are no longer able to interbreed and two distinct species are developed. There are two classes of speciation. Allopatric speciation occurs when two populations are separated by physical barriers such as mountains, rivers, canyons or oceans. Sympatric speciation takes place when two population groups share a habitat but do not mate as a result of biological factors such as changes in the chromosomes and mating habits that are mutually exclusive. After millions of years of speciation occurs there are so many different genetic variations that life as we know it today develops.

The main factor in adaptive evolution is natural selection. As a population group is introduced to a new environment where new challenges threaten the survival of the population then the individuals who possess genes that are most suitable for survival in the new environment coupled with continued change from generation to generation eventually lead to new and more suitable individuals living in any one particular environment. As the population carries on for generation after generation a new species appears which has fully adapted to the new environment.