How does genetic drift affect the diversity of organisms in a population?
Genetic drift decreases genetic diversity within a population. It is a change in allele frequencies due entirely to random chance and is more likely to affect smaller populations than large ones. Population bottlenecks can lead to genetic drift.
In the image below, we can see how genetic drift has caused only the blue butterflies to reproduce. Random events mean that the green and red butterflies were unable to produce offspring, thus the second population has a different genetic makeup than the first and the diversity is lower.
Genetic drift can play a role in the development of a new species. By randomly changing the allele frequency within a population, if those changes are sustained over time and are distinct enough from other populations, a new species can form.