Which observation would best support that dolphins and whales share a common ancestor?

• A. They Have Similar Anatomies.
• B. They Swim the Same Way.
• C. They Eat the Same Food.
• D. They Live in the Same Area of the Ocean.

Answer: (A)

Similar anatomies point to a shared evolutionary origin. When dolphins and whales have forelimbs that show the same basic bone pattern as other mammals, it signals that these body parts came from a common ancestor and were inherited, then modified for life in the ocean. This kind of shared internal structure, called a homologous feature, is strong evidence of descent with modification over time. In contrast, swimming style, diet, or living in the same area can arise for reasons tied to an environment or ecological niche and don't by themselves prove a shared ancestor. So the best clue that dolphins and whales are related through a common ancestor is their similar anatomy.