Final answer:
Genetic drift is influenced by small population sizes because each individual has a bigger impact on the gene pool and random events can significantly alter allele frequencies.
Step-by-step explanation:
What could cause genetic drift to occur within a population? The correct answer is d) Small population size.
Genetic drift is a mechanism of evolution that refers to random fluctuations in the frequencies of alleles from one generation to the next. These fluctuations are more pronounced in small populations because each individual's genetic makeup represents a larger proportion of the gene pool. Therefore, if an individual does not reproduce or dies before reproducing, the alleles it carries can significantly change the genetic structure of the population.
Examples of occurrences that can lead to genetic drift include chance events like accidental deaths or natural disasters, which may disproportionately affect certain alleles within the population.