Convergent evolution occurs when two or more distinct species evolve to display similar physical features that were not present in their latest common ancestor. Environmental circumstances that require similar developmental or structural alterations for the purposes of adaptation can lead to convergent evolution. For example, the wings of all flying animals are similar because the same laws of aerodynamics apply. These laws determine the specific criteria that govern the shape for a wing, the size of the wing, or the movements required for flight. All these characteristics are irrespective of the animal involved or the physical location. In various species of plants, which share the same pollinators, many structures and methods of attracting the pollinating species to the plant are similar. These particular characteristics enabled the reproductive success of both species due to the environmental aspects governing pollination, rather than similarities derived by being genetically related by descent.
One of the best examples of convergent evolution is how birds, bats, and pterosaurs learned to fly (all in different classes—birds, mammals, reptiles—that evolved along distinct lineages at different times). Importantly, each species developed wings independently. These species did not evolve in order to prepare for future circumstances, but rather the development of flight was induced by selective pressure imposed by similar environmental conditions, even though they were at different points in time. The development potential of any species is not limitless, primarily due to inherent constraints in genetic capabilities. Only changes that are useful in terms of adaptation are preserved. Yet, changes in environmental conditions can lead toward less useful functional structures, such as the appendages that might have existed before wings. Another change in environmental conditions might result in alterations of the appendage to make it more useful, given the new conditions.
Understanding the reason why each different species developed the ability to fly relies on an understanding of the possible functional adaptations, based on the behavior and environmental conditions to which the species was exposed. Although only theories can be made about extinct species and flight since these behaviors can be predicted using by fossil records, these theories can often be tested using information gathered from their remains. Perhaps the wings of bird or bats were once appendages used for other purposes, such as gliding, sexual display, leaping, protection, or arms to capture prey. Convergent evolution is supported by the fact that these species come from different ancestors, which has been proven by DNA analysis. However, understanding the mechanisms that brings about these similarities in characteristics of a species, despite the differences in genetics, is more difficult.
Convergent evolution creates problems for paleontologists using evolutionary patterns in taxonomy, or the categorization and classification of various organisms based on relatedness. It often leads to incorrect relationships and false evolutionary predictions.
Mindell, David P. The Evolving World: Evolution in Everyday Life. Cambridge, MA: Harvard University Press, 2006.
Grant, Peter R., et al. “Convergent Evolution of Darwin’s Finches Caused by Introgressive Hybridization and Selection.” Evolution. 58 (2004) 1588-1599.
PBS. “Convergent evolution.” Evolution Library. 2001. <http://www.pbs.org/wgbh/evolution/library/01/4/l_014_01.html> (accessed October 31, 2006).
Bryan Cobb, PhD