Final answer:
Aquatic vertebrates have streamlined bodies and appendages like fins and flippers due to evolutionary adaptations to reduce drag in the water, enhancing efficiency in their respective environments.
Step-by-step explanation:
The observation that most aquatic vertebrates like fish, penguins, and whales have streamlined bodies and fins or flippers for steering is primarily a result of evolution. The streamlined shape of aquatic animals is an adaptation to reduce drag forces in the water, which helps them move more efficiently. For example, as vertebrates transitioned from water to land, body design had to evolve to overcome new challenges. Fish retained their lateral undulation when moving onto land, and the fins that were previously used to push against water became points of contact with the ground.
Similarly, the shape of birds, such as migratory species that travel long distances, is streamlined to reduce drag while flying. Even in humans, the design of sperm is streamlined for energy efficiency. The evolution of body design for different forms of locomotion demonstrates the profound effect of environmental conditions on the physical characteristics of organisms through natural selection.