Sunday, March 7, 2010

Vestigial Organs

From pgs. 56-64, Coyne has a whole section about vestigial organs: organs that animals have but don't really need. Some examples of vestigial organs that Coyne gave were the human appendix and the wings of flightless birds. What other examples of vestigial organs are there? Theorize what purpose they could've served in ancestors of today's animals and plants.


  1. One example of a vestigial organ seen in many animals today is vestigial eyes. According to Coyne, many burrowing animals live in complete darkness and therefore don't necessarily need eyes to survive. However, based on these animals' evolutionary history, it has been shown that they descended from species that lived aboveground and had functioning eyes. However, eyes took energy to build and could be easily injured, so it was advantageous to these creatures when mutations that resulted in eye loss occurred. For example, the blind mole rat spends its entire life underground and yet has a vestige of an eye hidden beneath a protective layer of skin. This remnant eye can't form images but it contains a photopigment that is sensitive to low levels of light and helps regulate its daily rhythm of activity. This finding reiterates the definition Coyne gave for a vestigial trait: "[A trait] is vestigial not because it's functionless, but because it no longer performs the function for which it evolved" (58). Previously, the ancestors of the blind mole lived above ground and used their eyes for vision purposes. However, as their environment and behavior patters changed and they went underground, having eyes was no longer a beneficial trait, so mutations that caused deficiencies in vision were favored. One reason for why the moles moved underground in the first place could be that there was less predation and more food available underground. As the function of the trait is no longer beneficial for survival, the likelihood that future offspring will inherit the "normal" form of it decreases. In some cases the structure becomes detrimental to the organism (for example the eyes of a mole can become infected).

  2. Another example of a vestigial organ that is seen in humans today is wisdom teeth. For most people today, these teeth seem to be a pain that causes more trouble to humans than it does benefit. According to Live Science, the wisdom teeth may have become vestigial for two reasons. The first reason states that our ancestors had larger mouths and that wisdom teeth served the purpose of helping to break down food like our other teeth do. It is proposed that the human jaw may have become smaller over time, which led to the wisdom teeth being too large to fit in the small mouth of a human, which led to the many problems humans experience today. Another reason wisdom teeth may be vestigial today is due to the improvemens in dental hygiene. Thousands of years ago, our ancestors did not know the importance of proper dental hygiene, causing them to lose their teeth at a much younger age. Since dental hygiene has improved so much, humans normally have a full set of teeth at age 18, leaving no space for the wisdom teeth to come in. For either of these reasons, wisdom teeth causes pain in humans due to a lack of space in the mouth, requiring their removal. Going along with what Sarah said, vestigial organs are not functionless just because they don't serve a clear function today. In the case of wisdom teeth, they probably served as an advantage for our ancestors whose diets consisted of larger pieces of food like meat and plants that required more chewing to break down. Wisdom teeth would be a selective advantage to our ancestors because they would help break down their food better, allowing them to absorb more nutrients and survive longer. Once wisdom teeth evolved in humans because it was a selective advantage, it was passed down to further generations. This is important in showing that evolution must exist. If there really was a creator, why would it give humans such an unadvantageous organ such as wisdom teeth when they only cause us pain? Traits are passed down unless they prevent an organism from reproducing, in which case the organism would die off and not pass on its genes. This would eventually lead to that trait decreasing in the population. Wisdom teeth were clearly not a disadvantage enough that they were eliminated from our genes. Since wisdom teeth were not eliminated, they were passed on from our ancestors and remain as a vestigial organ that shows evolution must be true.

  3. As you have addressed in your question vestigial organs are organs animals have, but do not need. One that Sara and Annie haven’t touched on is the ear muscles. You might see people be able to move their ears while others can’t even make them wiggle. This is because our ancestors needed the ability to move their ears in order to focus on sounds around them. These muscles are still used with animals like cats when they are trying to localize sound they hear in their environment. According to Coyne, “species moving their ears helps them ddetect predators, locate their young, and so on” (64). For us the ability is useless as predators aren’t much of a threat to us now. Another vestigial organ we don’t use much now is called the arrector pilli and as Coyne explains its, “the tiny muscles that attach to the base of each body hair,”. You might see when cats or dogs get angry the fur on the back of their necks or spines stands up. This is a behavior in order to make the animal look bigger and more intimidating. Also known as goosebumps, they also raise on animals when they are cold in order to keep them warm. Humans don’t have as much hair and we have no need to look more intimidating by puffing up our hair. In result, again arrector pilli is useless, unless you count proving how cold you are.

    the book

  4. Another example of a vestigial structure is the occipitofrontalis muscle. Its current use in apes is to keep the head from falling off, since apes' heads are not balanced on a spinal cord and thus need "strong muscles to pull back on the skull" ( In humans, the muscle still has a use, just not its original one; this is why it's vestigial. The muscle "draws the scalp back which raises the eyebrows and wrinkles the forehead" (absoluteastronomy). Thus, the muscle's new function is to facilitate human facial expression.

    In my research to answer this question I found that many organs that were once considered vestigial have now been proved useful and important, such as the appendix and the tonsils, which both have roles in immunity, and the tailbone, which helps us sit (
    To connect to Sara's post, it has been found that body hair "assist[s] olfactory (relating to smell) communication" ( The article just cited discusses the importance of olfactory communication - for example, a baby can pick out his mom's smell, and "a mother's pheromones can calm a baby even when mom is absent."