Question

What does it means for a trait to have evolved convergently. Be sure to include the terms ancestor and descendant. Give one example of convergent evolution in nature, and explain what makes it convergence rather than homology.

Answer 1

Convergent evolution is the process of evolution in which two different, unrelated species (which do not share a common ancestor) develop similar traits through adaptation to similar environmental conditions. The descendants resemble each other more than their ancestor (with respect to the common trait evolved).

Example- evolution of wings in birds, bats and pterosaurs (extinct). Birds come under class : Aves, bats are mammals, pterosaurs are reptiles. All of them have very distant common ancestors. According to fossil studies wings evolved at first in pterosaurs (flying reptiles) followed by birds and mammals.

Though these 3 groups share a common trait ie wings for flight, structurally the wings are quite different among the three species. The wings are formed in pterosaur through the elongation of  fourth finger. Bat wing formed of a flap of skin stretched between the bones of the finger and arm. Elongated radius, ulna and forefinger bones fused to support wings in birds. These structural dissimilarity indicates there is not at all a possibility for a common ancestor with wing for the 3 species . There is no common ancestor.

Wings of bats, birds and pterosaur are analogous structures with seperate evolutionary origin. The structures which are superficially similar because of the similar environmental conditions and similar process of natural selection that lead to development of a structure that play key role in flight, is an example for analogous organ. Analogous structures are thus produced as a result of convergent evolution, whereas homologous structures have common evolutionary origin.