1. Vestigial Organ: Undeveloped Eyes on
Blind Mole Rats
The blind mole rat (Spalax typhlus) has tiny eyes completely
covered by a layer of skin. The blind mole rat is completely
blind and is unable to see any light. Blind mole rats spend
most of their time digging about ½ foot to 2 feet
underground, looking for roots and underground vegetation
to eat.
Their eyes begin to form as they develop, but a layer of skin
grows over them and their lenses and corneas do not form
correctly. Scientists have determined that the cells in the eyes
of these blind mole rats could still respond to light, but no
light reaches them in their current location, underneath skin
and fur.
2. Vestigial Organ: Human Appendix
Humans have a small part on the end of their intestines called
an appendix. Many modern species have a similar organ,
which is used to digest cellulose and other materials from
plants. The human appendix has lost this function and we are
no longer able to digest those substances. Some carnivorous
animals may have appendices too. Because these species do
not rely on these plant materials to survive, we do not need to
digest them to survive.
Research suggests that the appendix may still have some use.
It could guard against the loss of bacteria that aid in digestion.
Intestinal bacteria in the appendix may support quick
replacement of the healthy bacteria after an illness, poisoning,
or antibiotic treatment depletes them in the colon.
3. Vestigial Structure: Wings on Ostriches
Ostriches have small wings, but do not fly. Wings are
complex structures specifically suited for flight, but ostriches
cannot use their wings to fly.
Even though they can’t fly, they can still have some use for
their wings. When they're running, they use their wings for
balance, extending them to the sides to keep from toppling
over. They also use their wings in mating displays, and spread
them out to shade their chicks from the harsh African sun.
Scientists have learned from studying ostrich DNA that they
are related to birds that can fly, but ostriches use their speed
and size to avoid predators and no longer need flight to
survive.
4. Vestigial Structure: Undeveloped Hind
Legs on Baleen Whales
Many species of whales have small leg bones buried deep
within the back of the body. Whales do not use the bones as
fins, legs, or any other functional part. In the baleen whale
above, the bones marked “C” indicate small undeveloped
hind leg bones.
In creatures that walk on their legs, these structures often
have many small bones and joints to allow for movement. In
whales like the one above, the bones are fused together and
do not move. These are not fins. They are located entirely
inside of the body of the whale and cannot be used for
movement.
5. Vestigial Structure: Muscles around the
Human Ear
Humans have muscles around the ears that have no function.
Some humans are able to wiggle their ears slightly, but they
cannot move their ears enough to serve any function.
Many mammals (like the one above) have far more
developed muscles than those of humans, and therefore have
the capability to move their ears to better hear potential
threats.
In humans, the ability to move the ear is not necessary
because they may turn the head from side to side, an ability
that not all animals have. A function once provided by one
structure is now replaced by another.
6. Vestigial Behavior: “Goosebumps”
reflex on Human Skin
A reflex in muscles of human skin can cause the condition
commonly known as “goosebumps.” Small bumps show on
human skin when people become excited, scared, or cold.
In many organisms, a similar reflex functions as a response
to cold, heat, and stress. This behavior could cause the
animal to look larger and more menacing by puffing out the
hair. It could also keep the animal from getting cold.
However, because humans do not have a full coat of body
hair, this reflex is useless.
7. Vestigial Gene: Human Enzyme for the
Production of Vitamin C (L-gulonolactone
oxidase)
Most plants and animals can produce their own vitamin C.
Dogs, cats, yeast, reptiles, and birds all synthesize their own
Vitamin C out of materials such as simple sugars. Humans,
on the other hand, need to consume vitamin C from sources
like orange juice, or else we could get a sickness called scurvy.
L-gulonolactone oxidase is a gene that is functional in most
other mammals and produces an enzyme that is used to make
Vitamin C. In humans and guinea pigs, a mutation disabled
the gene and made it unable to produce the enzyme.
However, the remains of the gene are still present in human
DNA as a vestigial genetic sequence.
8. Vestigial Structure: Human Tail Bone
(Coccyx)
The coccyx, or tailbone, is the remnant of a lost tail. All
mammals had a tail at one point in their development. In
humans, it is present for a period of 4 weeks, during the time
an embryo is developing. This tail is most visible in human
embryos 31–35 days old.
The tailbone is located at the end of the spine, below the hip
bones. It has lost its original function in assisting balance and
mobility, but it still serves some other functions, such as
being an attachment point for muscles, which explains why it
has not disappeared entirely.