The mammalian tail and the human coccyx (tail bone) differ in their functions, but the close resemblance of these structures indicates a common evolutionary origin. \( \begin{array}{r}\text { The flippers of both penguins and } \\ \text { dolphins help them swim, but } \\ \text { the internal structures of the } \\ \text { flippers vary. }\end{array} \)

The passage discusses the concept of evolutionary biology, specifically focusing on homologous structures and convergent evolution. Let's break down the key points: 1. **Homologous Structures**: The mammalian tail and the human coccyx (tailbone) are examples of homologous structures. They have a common evolutionary origin, but their functions have diverged over time. The mammalian tail serves various functions such as balance and communication, while the coccyx in humans is a remnant structure with no significant function. 2. **Convergent Evolution**: The flippers of penguins and dolphins illustrate convergent evolution. Although both animals have flippers that serve the same function (swimming), their internal structures are different. This indicates that they evolved independently in response to similar environmental challenges, rather than from a common ancestor with flippers. In summary, the passage highlights how different evolutionary paths can lead to similar adaptations (convergent evolution) and how structures can retain a common origin while serving different functions (homologous structures).