Answer:
A. fitness
Step-by-step explanation:
Fitness, also known as 'evolutionary fitness', refers to the ability of one species/population/individual to survive and reproduce in its environment. Fitness is a fundamental concept in the evolutionary theory proposed by Darwin, because this concept highlights the importance of natural selection as the key mechanism by which evolution occurs. Fitness can be measured as the success of passing genes associated with specific phenotypic traits to the next generation.