Biology STAAR (State of Texas Assessments of Academic Readiness) Practice Test

What are homologous structures?

1. Structures that are only found in one species

2. Structures that serve different purposes in different species

3. Structures that are similar due to evolution from a common ancestor

4. Structures that have completely different origins

The correct answer is: Structures that are similar due to evolution from a common ancestor

Homologous structures are defined as anatomical features that are similar in different species because they have evolved from a common ancestor. This concept highlights the evolutionary relationships between species, showing how divergent evolution can lead to distinct forms and functions from a shared starting point. For example, the forelimb of a human, a whale’s flipper, and a bat’s wing all exhibit similar bone structures, reflecting their common ancestry, even though they perform different functions today. The emphasis on common descent underscores the idea that these structures can provide significant evidence for the theory of evolution. When studying biological diversity, homologous structures highlight how species adapt to their environments while retaining features derived from their evolutionary lineage. In contrast, structures that serve different purposes in different species (like those indicated in other choices) can be categorized as analogous structures, which arise independently in unrelated lineages and do not signify a direct evolutionary relationship.