Homology vs. Homoplasy
by Hailey, Lauren, Megan & Verenice
How do we recognize the difference between a homologous vs. a homoplastic structure?
A homologous structure is a structure that is found in multiple organisms that share a common ancestor. They are variations of each other but the function is the same. An example of homology is the skeletal structures of bats and humans. A homoplastic structure is similar in appearance but it has evolved from a different ancestor than the ancestor of the organisms that have a homologous structure. Different kinds of homoplasy include: convergent evolution and parallel evolution. Convergent evolution is the independent evolution of similar structures with similar functions in organisms from different lineages. They do not share a common ancestor and usually evolve similar traits because they are living in similar environments. An example of convergent evolution is an aardvark and an anteater, they appear similar but do not share a common ancestor. Parallel evolution is when two species that are related but distinct, continue to independently evolve similar structures. They share a distant common ancestor but belong to different clades. An example of Parallel evolution is a jerboa and kangaroo rat, they have distinct ancestors but are still closely related.
Describe several examples of homology and several examples of homoplasy.
Examples of homology:
- Hairs on mammals:
- Cows, bears and humans have different kind of hair but they are all used for insulation (trapping heat).
- Plant leaves:
- In the pitcher plant, the leaves modified into pitchers to catch insects
- In the venus fly trap, the leaves modified into “jaws”
- In a cactus, the leaves modified into spines
- Forelimbs of tetrapods: They have a humerus, radius, ulna, and phalanges
- The human pelvis is homologous to the pelvis of a dog and cat.
- The arm of a human, the wing of a bird or bat, the leg of a dog and the flipper of a dolphin or whale are homologous structures. They are different and serve a different purpose, but they are similar and share traits.
Examples of homoplasy:
- Wings of flies and wings of birds: an example of convergent evolution because both species evolved similar wing structures but do not share any common ancestor.
- Sharks and dolphins have a fusiform shape and they have a very similar physical anatomy but they did not descend from the same ancestor. Dolphins are mammals while sharks are considered fish.
- Distinct species of freshwater threespine sticklebacks have independently evolved from marine species to have smaller pelvic girdles, shorter dorsal spines, and less body armor.
- Jerboa and Kangaroo Rat both developed long limbs but they are not found in their common ancestor
- Human and octopus eyes are very similar in the structures that make up the eye but they develop differently and they do not share a relatively recent common ancestor.
- Squid and falcon beak: A squid and a falcon both have a beak, however, it is apparent that they did not acquire this trait from a common ancestor. The beaks evolved through convergent evolution.
- Bat wings are homoplasies because many species with similar bone structure do not have wings, including humans. To be specific, humans developed fingers while bats and birds developed wings to better fit their environment.
Why are homologies, not homoplasies, essential to phylogenetic analyses?
Homologies are similar features that multiple species share. We believe that individuals or species that are more closely related will tend to share more similarities than others who are more distantly related. If more characteristics are shared that leads to a conclusion that there is a shared common ancestry. Recognizing homologous structures is an important way to understand evolutionary relationships and explain how closely related organisms are.
References:
http://www.ucmp.berkeley.edu/education/events/carlson2.html
https://evolution.berkeley.edu/evolibrary/article/lines_04
Hall, Brian K., and Wendy M. Olson. Keywords and Concepts in Evolutionary Developmental Biology. Discovery Publishing House, 2007.
Schluter, Dolph, et al. “Parallel Evolution and Inheritance of Quantitative Traits.” The American Naturalist, vol. 163, no. 6, 2004, pp. 809–822., doi:10.1086/383621.
