The significance of homologous structures in evolutionary biology lies in their role as evidence for common descent among species. These structures share a similar anatomical origin but may serve different functions in different species. For example, the forelimbs of humans, whales, and bats all have a similar bone structure, indicating a shared evolutionary ancestor. The study of homologous structures helps scientists understand evolutionary relationships and the process of adaptive radiation, where species evolve different traits based on their environments.