What do homologous structures indicate about organisms?

Homologous structures provide evidence that different organisms share a common ancestry, showcasing the evolutionary relationships among species. These structures are formed from the same embryonic tissues and have similar anatomical features, although they may serve different functions in the respective organisms. For instance, the forelimbs of humans, whales, and bats all share a similar bone structure but are adapted for various functions like grasping, swimming, and flying, respectively. This divergence into different functions, while retaining the underlying structural similarities, highlights how adaptation occurs over time in related species, reinforcing the concept of common descent in evolutionary biology.