Final answer:
Natural selection favors individuals with traits that enhance their chances of survival and reproduction, such as better running speed. Therefore, faster mice would have been selected and bred over slower ones following the principle of directional selection favoring the extreme phenotype that provides a survival advantage.
Step-by-step explanation:
The question is asking whether faster mice or slower mice were selected and bred in relation to a principle of natural selection. Natural selection is a mechanism that increases the frequency of beneficial genetic traits over time. Specifically, it often favors individuals with adaptations that enhance survival and reproduction in a given environment.
The concept of natural selection producing beneficial adaptations, such as better running speed, indicates that faster individuals that run more frequently would likely have increased chances of survival and reproduction. Therefore, when it comes to breeding mice for speed, natural selection would favor the faster mice, leading to the hypothesis that faster mice were selected and bred, rather than the slower ones.
It is important to note that without specific context or information about the goals of a mating strategy, the general principle suggests that traits which confer a survival advantage, like superior speed to evade predators, will be favored by natural selection. This aligns with what is known as directional selection, where natural selection favors one extreme phenotype over another, leading to a shift in the population's genetic variance towards that phenotype - in this case, speedier mice.