Final answer:
Natural selection is the process by which heritable traits that improve an organism's survival and reproduction become more common in a population over time. A trait like better running speed, if advantageous for survival, will be passed down to future generations, leading to adaptive evolution of the species.
Step-by-step explanation:
Natural selection is a fundamental process in the theory of evolution, which leads to adaptive evolution. When an organism exhibits a heritable trait that improves its chances of survival and reproduction in its environment, such as better running speed, it is considered an adaptation. This advantageous trait can be a result of genetic variation favored by natural selection.
For instance, if the selective pressure in an environment is predation, individuals who can run faster may avoid being eaten and have a higher chance to survive and reproduce. Over time, because these faster individuals are more likely to survive and pass on their genes, the trait for better running speed becomes more prevalent in the population. Adaptations constantly mold a species, allowing it to stay fit to its ever-changing environment.
It's important to note that natural selection does not induce mutations or create adaptations directly, but it does select for beneficial mutations, like better running speed, once they occur. Unlike artificial selection, where breeders intentionally select for certain traits, natural selection occurs without human intervention and is driven by the pressures of the environment.