Genetic drift is a mechanism of evolution that occurs by random chance rather than natural selection. In genetic drift, a population experiences a change in the frequency of a given allele, prompted by random luck rather than a need for adaptation. This differs from natural selection, in which allelic frequency is altered based on the fittest genes surviving to reproduce and the weaker genes dying off. Genetic drift tends to be a phenomenon amongst smaller populations, while natural selection holds sway in larger populations. Life (168) Genetic drift can also occur through a random sampling error. A sampling error occurs when a sample exhibits different results than the entire population would. For example, say there are fifty red worms and fifty white worms in a population, and scientists randomly select ten worms to observe. Because the sample is smaller, the alleles passed on in the group of ten may not even out as they would in a group of one hundred. Also, if the group contains more red worms than white, the presentation of alleles in the offspring will be skewed. There are two types of genetic drift; there is a population bottle neck effect and the founder effect. The population bottle neck effect is when a population greatly decreases in size due to some random ecological event and the small population has a greater chance of genetic variation. The founder effect is a variation of the bottle neck effect in which a small portion of a larger population to branch off or get "isolated" from the larger population and have a greater chance of genetic variation.
