Tuesday, March 16, 2010

Vestigial Trait

On page 57, Coyne describes how a specific body part of an ostrich is a vestigial trait. What is a vestigial trait and how does it relate to an ostrich? Do you think it was beneficial that the function of this body part has changed? Why? Relate it to our big theme- structure and function. Also, what other animals exhibit vestigial traits?


  1. A vestigial trait is a feature of species that was an adaption in its ancestors, but that has either lost its usefulness completely or has been co-opted for new uses. The wings of the ostrich are a vestigial trait. Ostriches did descend from flying ancestors. This is has been proven through the fossil evidence and pattern of ancestry that flightless birds carry in their DNA. The wings in an ostrich no longer give them the ability to fly; however, they have developed new functions. They help the bird maintain balance, mate, and threaten its enemies. In some flightless birds, like the kiwi, the wings are so small and buried beneath their feathers, that they don't seem to have any function at all. In the penguin, however, they have developed new uses. They have evolved into flippers, which allows penguins to swim underwater with fantastic speed. Although the wings of birds may differ, they all have the same bones that are seen in the wings of birds that can fly. The concept of vestigial traits and their functions has a lot to do with the biological theme of structure and function. The parts of the body have specific structure and shape that enable them to perform functions that aid the organism to mate, find food, and protect itself from danger, which enhances its ability to survive and reproduce. Once a trait that all individuals of a species possess becomes less and less useful, the individuals with a structure slightly different that gives them an advantage over the majority of their species are favored and pass on these new genes. Through natural selection, certain structures are altered, which in turn aid individuals by carrying on the necessary functions more efficiently with less energy or less ware and tear on their bodies. Natural selection can favor certain genes that completely alter a structures function, like in the wings of a flightless bird, making them smaller and aiding them in swimming or mating. Other vestigial traits are the eyes of many animals. Burrowers and cave dwellers live in complete darkness. They descended from species that lived above ground and had functioning eyes, however. Eyes are a burden when you don't need them because they can be easily injured. Any mutations that favored their loss was clearly advantageous for species that lived in environments where it was too dark to see. The loss of eyes occurred in the easter Mediteranean blind mole rat, which spends its entire life underground. It has a vestige of an eye. Its eye is a tiny organ only one millimeter across and completely hidden beneath a protective layer of skin. "Some snakes have tiny pelvic bones and limb bones, and some cave-dwelling salamanders have eyes even though members of the species are completely blind." (http://bioweb.cs.earlham.edu/9-12/evolution/HTML/live.html) Another example of a vestigial organ exists in the whale. "All tetrapods (including whales) have pelvic bones. In most animals the pelvic bones are needed in order to be able to move the lower or rear set of limbs for the purpose of locomotion. In some species, such as whales, these limbs don't exist for the most part — although vestiges of them may remain. Perhaps they serve some function such as helping to support the whales reproductive anatomy, but there are many different types of structures which would be better suited to such a task." (http://atheism.about.com/od/evolutionexplained/a/VestigialOrgansAppendix.htm)

  2. Although their are many vestigial organs found in numerous species throughout, one source, http://www.answersingenesis.org/tj/v14/i2/vestigial.asp,believes "in the past, evolutionists claimed that there were approximately 180 vestigial organs in humans, including the appendix, the tonsils, the pineal gland and the thymus. Now we know that: The appendix is part of the immune system, strategically located at the entrance of the almost sterile ileum from the colon with its normally high bacterial content. The tonsils have a similar function in the entrance to the pharynx. The pineal gland secretes malatonin which is a hormone that regulates the circadian rhythm and has other functions. The thymus is part of the immune system, related to T-cells. HIV attacks T-cells, rendering them ineffective and for this reason is always eventually fatal. The number of organs that once were believed to be functional in the evolutionary past of humans but are non-functional today has been steadily reduced as the fields of anatomy and physiology have progressed." Another source, http://www.darwinismrefuted.com/embryology_02.html, explains how one evolutionist went as far as to say that vestigial organs are no proof for evolution; "These "non-functional organs" were in fact organs whose "functions had not yet been discovered." The best indication of this was the gradual yet substantial decrease in evolutionists' long list of vestigial organs. S. R. Scadding, an evolutionist himself, concurred with this fact in his article "Can vestigial organs constitute evidence for evolution?" published in the journal Evolutionary Theory: Since it is not possible to unambiguously identify useless structures, and since the structure of the argument used is not scientifically valid, I conclude that 'vestigial organs' provide no special evidence for the theory of evolution." Whether or not vestigial traits are classified correctly or not, it is true that the structures of different traits among species can alter due to a rapidly changing environment in order to aid the body so that it carries out its functions necessary to survive and reproduce.