Expiation:
Scientists often find cases in which a feature of an organism from one species is structurally similar to a feature of an organism from a different species. The features may perform very different functions in each species. This may indicate that the two species have a common ancestor.
If one community of a species experiences a long-term change in its environment, this community may undergo adaptation to survive in the new environment. Eventually, this community may even develop into a new species. The structures of the organisms in the new species may have new functions, while still resembling the structures of their ancestors. This would explain how similar structures can have very different functions in two or more species.