Final answer:
The experiment with guppies conducted by John Endler shows the relative importance of sexual selection and natural selection, with guppies adapting coloration based on predation and mate choice. When predators were removed, guppies developed brighter colors due to sexual selection. However, when predators were added back, guppies reverted to drab colors due to natural selection.
Step-by-step explanation:
The experiment with guppies conducted by John Endler demonstrates the relative importance of sexual selection and natural selection. Guppies with brighter coloration are preferred by female guppies, which shows the role of sexual selection. On the other hand, guppies that experience greater predation become more drab-colored to camouflage themselves from predators, illustrating the impact of natural selection. When predators were removed, the guppies relocated to the predator-free area developed brighter colors over time, indicating that sexual selection becomes more important in the absence of predators. However, when predators were reintroduced, the relocated guppies reverted back to drab colors due to natural selection.