JMSS Science Practice Test

Comparative anatomy shows how related organisms share a common heritage that has been modified over time. When you compare the skeletons of different vertebrates, such as humans, cats, whales, and bats, you often find a similar arrangement of bones in their forelimbs. That pattern isn’t just about what the limbs do today; it reflects a shared blueprint inherited from a single ancestor. Over millions of years, each lineage tweaked that blueprint to fit its environment, but the basic bone arrangement remains, signaling a distant common origin. That’s why the best choice is that they share a common ancestor in distant evolutionary past. The other ideas don’t fit because the observed structural similarity points to relatedness, not complete independence or no relationship; and comparing species isn’t about being the same species.