Homoplasies, Similar Character Traits

Characteristics Found in Unrelated Species Based on Function

Feb 23, 2009

A homoplasy is a feature shared by different organisms that was not present in their most recent common ancestor. Homoplasies demonstrate adaptation in the living world.

Homoplasies are evidence that certain environments mold organisms into survivalist machines. For example, the wings on bats and birds are homoplasies. They were not present in their most recent common ancestor, but they were formed independently by the two creatures' necessity for flight. Fins on mammals (cetaceans, such as porpoises and whales), extinct reptiles (ichthyosaurs), and fish are also homoplasies, as they are exhibited by these animals based on function, rather than relation. Dictionary.com summarizes the "homoplasy" satisfactorily with this definition: "correspondence in form or structure, owing to a similar environment." Homoplasies are amazing because they demonstrate a fundamental aspect of life: the ability of organisms to adapt.

Homologies are similarities found in separate species that were also found in their most recent common ancestor, meaning the subject character traits were not necessarily formed to help the organisms adapt to new environments. For example, the fins on a swordfish and an anchovy are homologies. Unlike homologies, homoplasies demonstrate a sort of evolution, which is depicted by changes in organisms that are determined by the environments they are subjected to. In an underwater habitat, animals require the ability to swim, so regardless of ancestry, different species that maintain successful underwater lives exhibit fins or some flat section on their body that may be used to propel themselves by pushing water, or direct themselves in it.

Homoplasy as Evidence of Evolution by Mutation

As a homoplasy requires the various species exhibiting the subject trait to have independent origins, it is perhaps the best evidence that organisms adapt and evolve by mutation. When the ancestors of cetaceans first took to the water, they were not equipped with fins but rather limbs with separated digits such as fingers and toes, much like the limbs of a wolf. In fact, pakicetus (the earliest known relative of cetaceans, which was a land dweller) looked something like a wolf. As this peculiar creature took more and more to the water, feeding on fish and marine life, individuals of later generations that exhibited mutations such as wide hands or feet, or webs between fingers and toes fared well, because they were better swimmers, and were able to feed easier. Mutations that caused the animals to be more streamlined, such as a straighter spine, also proved successful. Those individuals that were born balder were faster because hair did not slow their swimming, and they lived to pass on the trait.

The story goes much the same with extinct ichthyosaurs of the Mesozoic era. Ichtyosaurs were marine reptiles that died out about 90 million years ago, and had bodies similar in structure to modern porpoises (mammals) and billfish, such as marlin, sailfish, and swordfish. But icthyosaurs also evolved from land-dwelling reptiles, and their fins and streamlined bodies resulted from mutation, as did the bodies of modern cetaceans.

Examining skeletal structures demonstrates that such traits as the fins on fish, icthyosaurs, and cetaceans, or the wings on bats, birds, and extinct flying reptiles such as pteranodons, are indeed homoplasies because the animals are unrelated, and these traits evolved independently. Studying the evolutionary history of different species allows us to confirm homoplasies where the subject trait was absent from the different organisms' ancestors, and therefore points to adaptation throughout these organisms' pasts.

There exist countless homoplasies in the living world. Spines on cacti and thistles, horns on dinosaurs such as the triceratops, and on the rhinoceros, scales on snakes and fish, and plates on stegosauruses and armadillos are examples of homoplasies developed independently as methods of defense, to name a few. Tails on unrelated animals that help with balance, gills on amphibians and fish, and wings or fins throughout the animal kingdom also fit the category, as unrelated organisms had convergent evolutions. Homoplasies are remarkable in that they demonstrate the capability of living organisms to adapt, and change, as required to by the environment. They also help us understand the past, and by understanding how organisms historically functioned, they could ultimately assist us in protecting the species we have today.

The copyright of the article Homoplasies, Similar Character Traits in Evolution is owned by Thomas Wyatt. Permission to republish Homoplasies, Similar Character Traits in print or online must be granted by the author in writing.