Final answer:
An adaptation like better running speed is a result of natural selection, where faster runners are more likely to survive and reproduce, which leads to their traits dominating the species' gene pool.
Step-by-step explanation:
An adaptation, such as better running speed, is directly related to the process of natural selection. When environmental pressures or competition within a habitat exist, individuals who can run faster may avoid predators more effectively, locate resources quicker, or find mates more readily. This gives them a survival advantage, meaning they are more likely to reproduce and pass on their beneficial traits to their offspring.
Over time, these advantageous traits become more common within the gene pool because the genes associated with such traits have a selective advantage. This is how natural selection leads to the evolution of species, ensuring that those with favorable traits, like better running speed, are more represented in successive generations. Therefore, the correct answer to the question is b) 'Faster runners dominate their species' gene pool', as they survive and reproduce more than their slower counterparts, making the trait of better running speed more prevalent.