Vestigial Organs or Organs that do not have a purpose pose a challenge to the Intelligent Design argument. Vestigiality is a term which describes characteristics of organisms such as anatomical structures which have lost all or most of their original function in a species through evolution. Here are 10 examples:
#1. The Wings on Flightless Birds: The ostrich
In 1798, a French anatomist, Étienne Geoffroy St. Hilaire, traveled to Egypt where he witnessed and wrote about a flightless bird whose wings appeared useless for soaring.
That bird was an ostrich, but he described it as a "cassowary", a term then used to describe various birds of ostrich-like appearance. Ostriches and cassowaries are among several birds that have wings that are vestigial.
Besides the cassowary, other flightless birds with vestigial wings are the kiwi, and the kakapo.
Wings are complex structures that are specifically adapted for flight and those belonging to these flightless birds are no different. They are, anatomically speaking, rudimentary wings, but they could never be used to give these bulky birds flight. The wings are not completely useless, as they are used for balance during running.
#2. Hind Leg Bones in Whales
For over 100 million years the only vertebrates on Earth were water-dwelling creatures, with no arms or legs, or so biologists believe. But at some point these "fish" began to develop hips and legs and eventually were able to walk out of the water, giving the earth its first land lovers.
Once the land-dwelling creatures evolved, some mammals moved back into the water. Biologists estimate that this happened about 50 million years ago, and that this mammal was the ancestor of the modern whale.
Despite the apparent uselessness, evolution left traces of hind legs behind, and these vestigial limbs can still be seen in the modern whale. Cases have been found where whales have rudimentary hind limbs in the wild, and examples are found in baleen whales, humpback whales, and in many specimens of sperm whales.
#3. Goose Bumps and Body Hair
Do you ever get goose bumps? Smooth muscle fibers that give humans "goose bumps" they are the erector pili. If the erector pili are activated, the hairs that come out of the nearby follicles stand up and give an animal a larger appearance that might scare off potential enemies and a coat that is thicker and warmer. Humans, though, don't have thick furs and our strategy for several thousand years has been to take the fur off other warm looking animals to stay warm. And the rest of that hair, though, is essentially useless as is the Erector Pili.
#4. The Human Tailbone
These fused vertebrae bones are the only vestiges that are left of the tail that other mammals still use for balance, communication, and in some primates, as a prehensile limb.
As our ancestors were learning to walk upright, their tail became useless, and it slowly disappeared. It has been suggested that the coccyx helps to anchor minor muscles and may support pelvic organs. However, there have been many well documented medical cases where the tailbone has been surgically removed with little or no adverse effects.
#5. The Blind Fish
The Astyanax Mexicanus is a species of fish known which dwells in caves deep underground off the coast of Mexico: it is blind.
The pale fish has eyes, but as it is developing in the egg, the eyes begin to degenerate, and the fish is born with a collapsed remnant of an eye covered by a flap of skin. These vestigial eyes probably developed after hundreds or even thousands of years of living in total darkness.
Now how do we know that eye is degenerate, but the fish can still be able to see? Can we test this evolutionary phenomenon. That the fish, under the right conditions could see?
Well to have the experiment a control subject is needed. And there is such a fish. In fact such a fish of the same species live right above, near the surface, where there is plenty of light. These fish have fully functioning eyes.
So to test if the eyes of the blind Mexicanus could function if given the right environment, scientists removed the lens from the eye of the surface-dwelling fish and implanted it into the eye of the blind fish. The results showed that after eight days or so an eye began to develop beneath the skin. By two months the fish had developed a large functioning eye with a pupil, cornea, and iris. The blind fish could now they see.
#6. Wisdom Teeth in Humans
Wisdom teeth, humans have become remnants from their large jawed ancestors. But regardless of how much they are despised, the wisdom teeth remain, and force their way into mouths regardless of the pain inflicted. Two reasons are possible to explain why the wisdom teeth have become vestigial. The first is that the human jaw has become smaller than its ancestors' and the wisdom teeth are trying to grow into a jaw that is much too small.
The second reason may have to do with dental hygiene. Thousand years ago, it might be common for an 18 year old man to have lost several, if not all of his teeth, and the incoming wisdom teeth would prove useful. Now with better dental hygiene it's possible to keep one's teeth for a lifetime.
#7. The Sexual Organs of Dandelions
Dandelions, like all flowers, have the stamen and pistil, the sex organs necessary for sexual reproduction, but they do not use them. Instead dandelions reproduce without fertilization. They clone themselves, and they are quite good at it. Look at any lawn for the proof.
#8. Fake Sex in Virgin Whiptail Lizards
Lizards of the genus Cnemidophorus exhibit certain vestigal behavior. Since only females exist in several species of the lizards of the genus Cnemidophorus, how to they propagate the species? The females reproduce by parthenogenisis. They don't need the males. Parthenogenisis is a form of reproduction in which an unfertilized egg develops into a new individual. Females just produce clones of themselves as a form of reproduction.
So why do the females try to copulate? Despite the fact that it is unnecessary and futile, the lizards still like to try, and occasionally one of the females will start to "act like a male" by attempting to copulate with another female. The lizards evolved from a sexual species and the behavior to copulate like a male -- to engage in fake sex is a vestigial behavior. So the sexual copulation behavior is present in a species, but is expressed in an imperfect form, in this case, is as a useless act. This is an example of vestigial behavior.
#9. Male Breast Tissue and Nipples
Both men and women have nipples because in early stages of fetal development, but in the early stages an unborn child is effectively sexless. Thus nipples are present in both males and females. In the later stages of fetal development when testosterone causes sex differentiation in a fetus does the sex of a fetus become apparent. Mammary glands are present in all mammals, male and female. And male nipples are vestigial; they may perform a small role in sexual stimulation and a small number of men have been able to lactate.
#10.The Human Appendix
The human appendix is a small pouch attached to the large intestine where it joins the small intestine. It does not directly assist digestion. Biologists believe it is a vestigial organ left behind from a plant-eating ancestor. In plant-eating vertebrates, the appendix is much larger and its main function is to help digest a largely herbivorous diet. This is not useful in Humans who consume plants and animals.
These are 10 examples of biological functions and artifacts that promote the idea that Intelligent Design is not intelligent. If it were intelligent, that is well designed, why are these vestigial elements present. And they are present on mammals, plants, birds, and fish, there is even vestigial behavior.