Question

if similar features are either homologous or analogous how can both be used as arguments supporting evolution

Answer 1

Evolution occurs when nature selects the best trait for each characteristic.

Analogous features refer to similar characteristics which have developed separately in two different lineages or ones which do not share a common ancestor. The two unrelated species, probably sharing similar environments, habitat or climatic conditions have developed these traits for adaptation and survival. The basic need of bats (a mammal), an eagle (bird) and a drosophila ( a flying insect) is to fly and therefore all have developed wings. However they do not share a common ancestor. But they have developed wings as a part of convergent evolution to survive. Similarly dolphins ( mammals) and shark ( fish) share the same marine habitat and have developed fins for swimming, however both do not share a common ancestor.

Homologous features, on the other hand refer to similarity in structure between different parts of different organism who have shared a remote ancestor. Bats and dolphins have a homologous limbs but their function and gross morphology is totally different. This is called divergent evolution. Migration to new habitats where survival is prime and competition with other species is high, species undergo changes to adapt to the new environment. Spines on the cactus and leaves of the oak tree are homologous, however, the spines provide protection and prevent water loss in the arid conditions.

Thus both the features support evolution – survival of the fittest as they say!