33.7: Convergent Evolution
Evolution shapes the features of organisms over time, ensuring that they are suited for the environments in which they live. Sometimes, selection pressure leads to the rise of similar but unrelated adaptations in organisms with no recent common ancestors, a process known as convergent evolution.
The structures that arise from convergent evolution are called analogous structures. They are similar in function even if they are dissimilar in structure. Further, structures can be analogous while also containing homologous features - those inherited from a common ancestor. Birds and bats have analogous wings, but the forelimb bones within their wings are homologous, adapted from a distant four-limbed ancestor. The wings of butterflies, on the other hand, are analogous to those of birds and bats, but they are not homologous.
Sometimes it is clear when two organisms share traits as a result of convergent evolution, as in the case of bird, bat, and butterfly wings, but at other times it is less obvious. To determine whether traits are analogous and thus the result of convergent evolution or homologous and the result of shared ancestry, scientists can examine the DNA sequences of the organisms in question.
Dolphins and many bats use echolocation to navigate and hunt. DNA sequence data has indicated that the gene Prestin, which encodes a protein in the mammalian cochlea hypothesized to confer high-frequency hearing, has evolved in a convergent manner across less-related bats and in a similar manner in dolphins.
Structurally-similar toxins and venoms in different species provides another example where DNA sequence data is critical for identifying whether a trait is analogous or homologous.