The top 10 Vestigial

Structures

10

The Wings on Flightless Birds • In general, wings of a bird are considered complex structures that are specifically adapted for

flight and those belonging to these flightless birds are no different. They are, anatomically, rudimentary wings, but they could never give these bulky birds flight. The wings are not completely useless, as they are used for balance during running and in flagging down the honeys during courtship displays.

9

Hind Leg Bones in Whales • Biologists believe that for 100 million years the only vertebrates on Earth were water-dwelling

creatures, with no arms or legs. 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, there were some mammals that 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.

8

Erector Pili and Body Hair • The erector pili are smooth muscle fibers that give humans goose bumps. 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 like their ancestors did, and our strategy for several thousand years has been to take the fur off other warm looking animals to stay warm.

7

The Human Tailbone (Coccyx) • These fused vertebrae 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.

6

The Blind Fish Astyanax Mexicanusand Blind Mole rat

• In an experiment designed by nature, the species of fish known as Astyanax mexicanus, dwelling in caves deep underground off the coast of Mexico, cannot see. 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 flap of skin. These vestigial eyes probably formed after hundreds or even thousands of years of living in total darkness.

5

Wisdom Teeth in Humans • With all of the pain, time, and money that are put into dealing with wisdom teeth, humans have

become just a little more than tired of these 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. There are two possible reasons 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. A few thousand years ago, it might be common for an 18 year old man to have lost several, probably most, of his teeth, and the incoming wisdom teeth would prove useful.

4

The Sexual Organs of Dandelions

• Dandelions, like all flowers, have the proper organs (stamen and pistil) necessary for sexual reproduction, but do not use them. Dandelions reproduce without fertilization; they basically clone themselves, and they are quite successful at it. Look at any lawn for the proof. If dandelions were to revert to sexual reproduction, they might not retain whatever traits they have that allow them to be pests to gardeners everywhere.

3

Fake reproduction in Virgin Whiptail Lizards (Vestigial Behavior)

• Only females exist in several species of the lizards of the genus Cnemidophorus, which might seem like a problem when it comes time to propagate the species. The females don’t need the males though, they reproduce by parthenogenesis, a form of reproduction in which an unfertilized egg develops into a new individual. So basically, the females don’t need the males; they just produce clones of themselves as a form of reproduction. Despite the fact that it is unnecessary and futile to attempt copulation with each other, 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.

2

Male Breast Tissue and Nipples • The subject of male nipples is a sensitive, and maybe confusing, topic to many. Those who wish

to invalidate evolutionary theory might pose the question, Was man descended from woman? The answer, of course, is no. Both men and women have nipples because in early stages of fetal development, an unborn child is effectively sexless. Nipples are present in both males and females; it is only in a later stage of fetal development that testosterone causes sex differentiation in a fetus. All mammals, male and female, have mammary glands.

1

The Human Appendix • In 2000, in fact, there were nearly 300,000 appendectomies performed in the United States, and

371 deaths from appendicitis. In plant-eating vertebrates, the appendix is much larger and its main function is to help digest a largely herbivorous diet. The human appendix is a small pouch attached to the large intestine where it joins the small intestine and does not directly assist digestion. Biologists believe it is a vestigial organ left behind from a plant-eating ancestor.

Analysis

1. Define vestigial.

2. How could vestigial structures be proofs for evolution?

3. Choose 2 of the structures mentioned and give an explanation for why they exist.

Answers

1. Vestigial: “remnant of” structure that is seemingly useless

2. Ancestors may have used that structure. Ex. Appendix was used to help digest high fiber foliage, but now we rarely eat roughage.