Natural selection and genetic drift are two mechanisms of evolution that can lead to speciation. Define both natural selection and genetic drift, describe how both can lead to speciation, and provide both a historic and potentially current example for each. Be sure to address selection pressures

Evolution

Explanation:                  

Genetic drift

Genetic drift is change in allele frequencies in a population from generation to generation that occurs due to chance events The genetic drift occurs due to random fluctuation of any allele in a gene pool and is more efficient in small populationThe founder effect and the bottleneck effect are cases in which a small population is formed from a larger population which means they may experience strong drift for generationsIn founder effect a genotype from a homogeneous gene pool migrate to a newer habitat and colonize there and form a newer community which leads to the genetic drift to the original population, speciation which occurs in this effect is the peripatric speciationIn bottleneck effect the elimination of inferior genotype from a homogeneous gene pool occurs due to the strong selection pressure and changing environmental conditions which leads to genetic drift and a only a few most adapted genotype survives and flourish

Natural Selection

Natural selection is a selection pressure which operates in a population and allow the best fitted genotype to survive in changing environmental conditions and eliminate the other genotype which are not fit Genetic drift, mutation and sexual selection are important causes of natural selectionDirectional natural selection favours the superior genotype and eliminate the inferior and intermediate genotype, in the history of evolution the most common natural selection is directional natural selectionStabilizing natural selection favours the intermediate genotype but eliminates the extreme genotype Bidirectional natural selection favours the extreme genotypes but eliminate the intermediate genotypes

Gravitational force i believe