Answer:
More individuals are produced each generation that can survive. Phenotypic variation exists among individuals and the variation is heritable. Those individuals with heritable traits better suited to the environment will survive.
Explanation:
Insects are an example of natural selection because insecticides kill of the insects that are not resistant. This means that the ones that are resistant will reproduce and pass on their genes to the next generation which increases the frequency of the resistant allele. This means that over time populations of insects will become more and more resistant to pesticides.
