The top 10
Vestigial
Structures
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.
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 landdwelling 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.
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.
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.
The Blind Fish Astyanax Mexicanus
and 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.
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.
The Sexual Organs of Dandelions
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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.
Fake reproduction in Virgin Whiptail
Lizards (Vestigial Behavior)
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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.
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.
The Human Appendix
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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.