Final answer:
Genetic drift decreases genetic variation within populations and increases genetic differences among populations, influenced by random chance events like the bottleneck effect which can drastically change the gene pool.
Step-by-step explanation:
Genetic drift tends to decrease genetic variation within populations and increase genetic differences among populations. This phenomenon is the result of random changes in allele frequencies that can have significant effects, especially in small populations. Events such as natural disasters can cause a bottleneck effect, where a large portion of a population's gene pool is suddenly wiped out, leading the surviving genetic structure to become representative of the entire population.
Genetic drift occurs because the alleles in the offspring are a random sample of the alleles in the parent generation, and random events can prevent certain alleles from being passed down. For example, if only white rabbits are killed in a storm, the allele for white fur may diminish or disappear. Thus, genetic drift can lead to a loss of alleles from a population and an evolution that is not driven by adaptation, but by chance, which may cause isolated parts of the population to diverge genetically over time.