Homology and Analogy – A lesson in Biology
By Sam Lucas
Comparative anatomy is the study of similarities and differences within the structures of organisms. Physical features may be considered homologous or analogous, but what does this mean?
Homologous structures are similar physical features in organisms that share a common ancestor, but the features serve completely different functions. An example of homologous structures are the limbs of humans, cats, whales, and bats. Regardless of whether it is an arm, leg, flipper or wing, these structures are built upon the same bone structure.
Homologies are the result of divergent evolution. Divergent evolution is the process in which organisms from the same common ancestor evolve and accumulate differences, often resulting in a new species. This may occur due to pressures such as changes in abiotic or biotic factors within the environment.
On the opposite side of the spectrum, analogous structures are similar physical features in organisms that do not share a common ancestor. Instead, these structures are related to one another because they perform the same function. An example of this are the wings of a bat and the wings of a bird. They have completely different bone structure, but their wings share the same function, allowing the animal to take flight.
Analogies are a result of convergent evolution. Convergent evolution is the process in which two organisms that do not share a common ancestor evolve and develop similarities independently of one another. These similarities form because the animals either live in comparable environments or they experience the same environmental pressures, resulting in the evolution of these features.
Next time you are comparing two organisms try to think about how they are related (or not) to one another. The answers may surprise you!