A city was intensively sprayed with DDT to control houseflies. The number of houseflies was immediately greatly reduced. Each year thereafter, the city was sprayed again, but the flies gradually increased in numbers until 10 years later, when they were almost as abundant as they were when the control program began. Which of the following most likely explains this?
A) Flies from other areas moved in and replaced the ones killed by DDT.
B) The few flies that were affected by DDT but survived developed antibodies to DDT, which they passed on to their descendants.
C) The DDT caused new mutations to occur in the surviving flies, resulting in resistance to DDT.
D) The DDT killed most flies. The few that were already naturally resistant survived and passed this resistance on to their offspring.

Question

Quizplus · Accepted Answer

The most likely explanation is natural selection resulting in the survival and reproduction of DDT-resistant individuals. These resistant individuals would have passed on their genes for resistance to their offspring, leading to an increasing proportion of resistant flies in the population over time. This process is an example of natural selection, where individuals with advantageous traits are more likely to survive and reproduce. Options A, B, and C are less likely explanations, as they all require unlikely scenarios such as large-scale migration of flies from other areas or rapid development of resistance through mutations or antibody production.

A City Was Intensively Sprayed with DDT to Control Houseflies