33.7:
Convergent Evolution
Bats and most birds share the ability to fly by flapping their wings. One might assume that these two groups evolved from a common ancestor with wings. In fact, bats and birds are not closely related, and their last common ancestor was a ground-dwelling animal with four limbs.
The evolution of wings is an example of convergent evolution—the independent evolution of similar features with comparable function.
The ability to fly evolved multiple times, which is evident upon closer inspection of the morphology of wings in birds and bats.
The hand and wrist bones of birds are fused, and feathers provide a large area to create lift. During flight, birds tuck their hindlimbs out of the way.
In contrast, the finger bones of bats are elongated and mount a large area of skin that makes up the wing. The hindlimbs of bats play an essential role in creating the wing.
Another example of convergent evolution can be found in whales and fishes. Whales are warm-blooded mammals that nurse their offspring and breathe air. Fish are ectotherms, lay eggs, and exchange gases using gills.
However, the requirements of life in water led to the evolution of similar—or analogous—features in whales and fishes. Both groups have fins and a streamlined body form to more easily move through the water.
Whales and fishes do not share a recent common ancestor, yet have analogous features with similar function due to convergent evolution.
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.
Suggested Reading
Brodie III, Edmund D. "Convergent evolution: pick your poison carefully." Current biology 20, no. 4 (2010): R152-R154. [Source].
Liu, Yang, James A. Cotton, Bin Shen, Xiuqun Han, Stephen J. Rossiter, and Shuyi Zhang. "Convergent sequence evolution between echolocating bats and dolphins." Current Biology 20, no. 2 (2010): R53-R54. [Source].
Parker, Joe, Georgia Tsagkogeorga, James A. Cotton, Yuan Liu, Paolo Provero, Elia Stupka, and Stephen J. Rossiter. "Genome-wide signatures of convergent evolution in echolocating mammals." Nature 502, no. 7470 (2013): 228. [Source].