What is the term for an organism's ability to survive and reproduce in its environment?

The correct answer is "fitness." In the context of evolutionary biology, fitness refers to an organism's capability to survive and reproduce in its specific environment. It encompasses not just survival but the relative reproductive success of an organism compared to others in the population. Fitness is often measured by the number of offspring an organism can produce that reach reproductive age, contributing to the gene pool of future generations.

Adaptability refers to the capacity of an organism to adjust to changes in its environment, which can contribute to its fitness but is not synonymous with it. Evolution is the process through which species change over time, driven by mechanisms such as natural selection, but it does not specifically describe the ability of an individual organism to thrive. Natural selection is the mechanism by which advantageous traits become more common in successive generations due to differential survival and reproduction, but it is a process rather than a characteristic of the organism itself. Understanding fitness is crucial for grasping how organisms evolve and adapt to their environments over time.