Final answer:
Populations may show low levels of genetic diversity due to a small initial population size, inbreeding, chance events, and differential survival and reproduction. These factors can contribute to the decline in genetic diversity over time.
Step-by-step explanation:
There are several reasons why populations might show very low levels of genetic diversity. One reason is a small initial population size, which can result in a decline in genetic diversity over time. Another reason is inbreeding, which occurs when closely related individuals mate and can lead to the accumulation of harmful recessive mutations. Additionally, chance events such as natural disasters and differential survival and reproduction can cause genetic drift, leading to decreased genetic diversity in a population.