Which term describes similarity of a trait due to shared ancestry rather than function?

• A. Analogy
• B. Vestigial organs
• C. Homology
• D. Embryology

Answer: (C)

Homology describes similarity of a trait because of shared ancestry, not because of what the trait does now. That means the trait is inherited from a common ancestor and kept through lineages, even if different species use it in different ways today. A classic example is the forelimbs of humans, cats, whales, and bats—they all have the same basic bone pattern (humorous, radius and ulna, carpals, metacarpals, and phalanges) arranged similarly, which points to a common ancestral limb. Over time, these limbs were adapted for different functions, but the underlying structure remains a record of shared origin.

In contrast, analogy refers to similarity due to function rather than shared ancestry, such as wings evolved for flight in different groups that didn’t inherit a winged ancestor. Vestigial organs are features that were functional in ancestors but are reduced or unused now, and embryology is the study of development, which can reveal homologous relationships but is not itself the term for similarity due to ancestry.