A farmer repeatedly sprays a synthetic insecticide on a vegetable farm over several growing seasons. Initially, the chemical kills nearly all target pests, but after several years, the insecticide loses its effectiveness and pest populations surge. According to Darwin's theory of natural selection, which of the following statements best explains how resistance arose in this insect population?
- AInsects exposed to non-lethal doses of the insecticide gradually built up immunity during their lifespan and passed this acquired tolerance to their offspring.
- A small fraction of insects possessed pre-existing genetic variations for resistance, enabling them to survive the chemical, reproduce, and transmit the resistant genes to subsequent generations.Answer
- CThe chemical spray induced targeted mutations in individual insects to allow them to adapt directly to the toxic environment.
- DSusceptible insects modified their behavioral habits to avoid contact with the chemical, resulting in physiological immunity over time.
Answer
Pre-existing genetic variation allowed resistant individuals to survive, reproduce, and pass advantageous alleles to their offspring.
According to Charles Darwin's theory of natural selection, evolution operates on pre-existing genetic variations within a population. When an environmental selective pressure (such as an insecticide) is introduced, individuals already possessing alleles for resistance are more likely to survive and reproduce. Over successive generations, these advantageous alleles become more common, increasing overall resistance in the population.
Step-by-Step Solution
Key Concept
Darwinian Natural Selection and Antibiotic/Pesticide Resistance