Final answer:
The streamlined body shapes of porpoises and sharks are an example of analogy due to convergent evolution, where these organisms have developed similar adaptations for efficient swimming in water despite being distantly related.
Step-by-step explanation:
The streamlined shapes of both porpoises and sharks are an example of analogy (similarity due to convergent evolution).
Porpoises and sharks have evolved similar body shapes not because they share a close recent evolutionary ancestry but because they have both adapted to similar environmental conditions.
This adaptation for moving efficiently through water is a classic example of convergent evolution, where distantly related species evolve similar traits independently due to similar environmental pressures.
Convergent evolution is the process where organisms that are not closely related independently evolve similar traits as a result of having to adapt to similar environments or ecological niches.
In the case of porpoises and sharks, their analogous body shapes are a result of adapting to life in aquatic environments, necessitating a streamlined shape for efficient swimming.