Which of the following best describes homologous structures?

Homologous structures are defined as anatomical features that share a common structural origin, reflecting a shared ancestry, even if their functions may differ. For example, the forelimbs of humans, whales, and bats all have similar bone structures (like humerus, radius, and ulna) but serve different functions in each species — like manipulation, swimming, and flying, respectively. This concept is crucial in understanding evolutionary biology as it demonstrates how divergent evolution can lead to different adaptations from a common ancestral form.

The reason this option accurately captures the essence of homologous structures is that it highlights both the similarity in structure and origin, which is foundational to the concept. In contrast, other options either emphasize functional similarities, environmental adaptations without a common origin, or limit the discussion to vertebrates, which does not encompass all homologous structures that can occur across various species.