environmental factors can influence natural selection because they can increase or decrease\nthe number of…

Brief Explanations:

Natural selection acts on the genetic variation within a population. Environmental factors can affect which traits are favorable or unfavorable, thus influencing the amount of genetic variation in a population over time. They do not directly change the number of chromosomes in an individual or population, nor do they directly change the amount of genetic variation in an individual (mutation is the main source of new genetic variation in an individual).

Answer:

the amount of genetic variation in a population.