Which of the following can result in a population looking more similar overtime and can be described as selections against both extreme of a trait

Stabilizing Selection; this type of natural selection selects against the extremes of a trait and favors only the intermediate phenotype, making the population look more similar overtime.

the principles and empirical processes of discovery and demonstration considered characteristic of or necessary for scientific investigation, generally involving the observation of phenomena, the formulation of a hypothesis concerning the phenomena, experimentation to test the hypothesis, and development of a conclusion that confirms, rejects, or modifies the hypothesis.

when it is at an intermediate population density