Question

environmental factors can influence natural selection because they can increase or decrease
the number of chromosomes in an individual.
the number of chromosomes in a population.
the amount of genetic variation in an individual.
the amount of genetic variation in a population.

Explanation:

To solve this, we analyze each option:

• Chromosome number in an individual or population isn't directly changed by environmental factors for natural selection (mutations causing chromosome changes are rare and not the main way env. affects selection).
• Genetic variation in an individual is relatively fixed (an individual's genetics don't change much due to environment in terms of variation).
• Environmental factors (like climate, predators, resources) can affect which traits are favorable, thus influencing the survival and reproduction of individuals with certain genetic variations, which in turn changes the amount of genetic variation in a population (e.g., if a new predator favors a certain trait, individuals with that trait survive, altering the population's genetic variation).

Answer:

D. the amount of genetic variation in a population.