Answer: The correct answer is-
Natural selection.
Step-by-step explanation:
Natural selection is an evolutionary theory that was given by Charles's Darwin. According to this theory, organisms that possess a beneficial allele (a gene variant) for their survival or that are capable of adapting themselves in changing environmental conditions, will survive and produce large number of offsprings through reproduction.
Thus, it means that if an organism becomes adapted to its environment, it will survive.
Therefore, Natural selection is the right answer.