EVIDENCE FOR EVOLUTION:
COMPARATIVE ANATOMY
By comparing the anatomy of different animals much
can be learned about their evolution.
HOMOLOGOUS STRUCTURES:
Bones in the forelimb of the human, whale, cat, bat,
bird, alligator are used for vastly different movement,
they all have remarkably similar structure and
organization (bones, nerves, blood vessels
This indicated common ancestry (DNA)
Organs with similar structure but different functions
are called HOMOLOGOUS STRUCTURES
COMPARATIVE ANATOMY:
Homologous Structures
COMPARATIVE ANATOMY:
Homologous Structures
COMPARATIVE ANATOMY:
Homologous Structures
COMPARATIVE ANATOMY:
Homologous Structures
COMPARATIVE ANATOMY:
Vestigial Structures
• Many animals have structures in their
bodies which seem to be of no use to
them
• These parts are called VESTIGIAL
STRUTURES
• In other species the same structures exist
and they have a definite function
COMARATIVE ANATOMY:
Vestigial Structures
Human Wisdom Teeth ARE Vestigial
COMPARATIVE ANATOMY:
Vestigial Structures
• Dogs & humans have
a similar set of
muscles attached to
their ears. The dog
can use these to
“point” its ears in the
direction of a sound,
humans cannot
• In humans the
appendix, coccyx and
hair are all vestigial
structures
COMARATIVE ANATOMY:
Vestigial Structures
TOP 10
VESTIGIAL
SRUCTURES
OF ALL TIME !
#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 waterdwelling 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. There are many cases where
whales have been found with rudimentary
hind limbs in the wild, and have been found
in baleen whales, humpback whales, and in
many specimens of sperm whales. Most of
these examples are of whales that had only
leg bones, but there were some that
included feet with complete digits. It was
reported recently that whales and hippos
were distantly related.
# 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. It,s ironic actually that
an animal, sensing danger is near, would puff
up its coat to look scarier, but the human
hunter would see the puffier coat as a warm
prize, leaving the thinner haired weaker
looking animals alone. Of course, some body
hair is helpful to humans; eye brows can
keep sweat out of the eyes and facial hair
might influence a woman’s choice of sexual
partner. All the rest of that hair, though, is
essentially useless.
# 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. There have been documented cases
of infants born with tails, an extended
version of the tailbone that is composed of
extra vertebrae. There are no adverse health
effects of such a tail, unless perhaps the
child was born in the Dark Ages. In that
case, the child and the mother, now
considered witches, would’ve been killed
instantly.
# 6 The Blind Fish:
Astyanax Mexicanus
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. As for the
experiment, a control is needed; and luckily
for us, fish of the same species live right
above, near the surface, where there is
plenty of light, and these fish have fully
functioning eyes. 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.
It was observed that within eight days an
eye started to develop beneath the skin, and
after two months the fish had developed a
large functioning eye with a pupil, cornea,
and iris. The fish were blind, but now they
see.
# 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. Now
that humans brush their teeth twice a
day, it’s possible to keep one’s teeth for
a lifetime. The drawback is that the
wisdom teeth still want to come in, and
when they do, they usually need to be
extracted to prevent any serious pain.
# 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. If flowers
can begin reproducing in this manner, does
that mean animals, even humans could too?
Asexual reproduction can be a good
strategy in an environment that is constant if
a species is well suited to those conditions.
It doesn’t take a scientist to figure out that
humans wouldn’t last long if the condition
set forth was no sexual contact with others.
Therefore, the human sexual organs are
probably in no danger of becoming vestigial.
# 3 Fake Sex in 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. The lizards evolved from a
sexual species and the behavior to
copulate like a male -- to engage in fake
sex -- is a vestigial behavior; that is, a
behavior present in a species, but is
expressed in an imperfect form, which in
this case, is useless.
# 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. Male
nipples are vestigial; they may perform a
small role in sexual stimulation and a
small number of men have been able to
lactate. However, they are not fully
functional and, because cancer can
grow in male or female breast tissue, the
tissue can be dangerous.
# 1 The Human Appendix
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. Interestingly, it has been noted by
paleontologist Alfred Sherwood Romer in his
text The Vertebrate Body (1949) that the
major importance of the appendix ?would
appear to be financial support of the surgical
profession,? referring to, of course, the large
number of appendectomies performed
annually. In 2000, in fact, there were nearly
300,000 appendectomies performed in the
United States, and 371 deaths from
appendicitis. Any secondary function that the
appendix might perform certainly is not
missed in those who had it removed before
it might have ruptured.
COMARATIVE ANATOMY:
Analogous Structures
• Features of different species that are similar in
function but are structurally different
• Do not have a common ancestry
• Evolved due to a similar environmental
challenge
• Ex) Birds & insects have wings to fly although
their wing structure is different
• Ex) Fat insulated, streamlined shapes of seals &
penguins
COMARATIVE ANATOMY:
Analogous Structures
COMARATIVE ANATOMY:
Analogous Structures
COMARATIVE ANATOMY:
Embryology
• Embryological development of all
vertebrates (fish to mammals) is
remarkably similar especially in the early
stages
• The more closely the related organisms,
the longer their embryonic development
proceeds in a parallel fashion
COMARATIVE ANATOMY:
Embryology
COMARATIVE ANATOMY:
Embryology
• Humans have gill pouches in early development
• In fish these pouches develop into gill slits
• In humans they form the eustachian tube and
auditory canal, which except for the eardrum,
are a direct connection between the outside of
the body and the pharynx
• Human embryo has a tail and body hair like
embryos of all other mammals but in the human
embryo these features disappear before birth
• The presence of these features provides
evidence that humans & other mammals
developed from common ancestors
COMARATIVE ANATOMY:
Embryology
COMARATIVE BIOCHEMISTRY
• In studying the complex molecules making
up the bodies if living things, we find
incredible similarities in the structures of
these molecules in various organisms.
• Closely related species are very similar at
the molecular level
• Distantly related species are more
dissimilar at the molecular level but
similarities still exits
COMARATIVE BIOCHEMISTRY
1. All cells are made up
of the same basic
types of organic
compounds: nucleic
acids, lipids,
carbohydrates
COMARATIVE BIOCHEMISTRY
2.In all organisms, reactions involving these
organic compounds are controlled by
proteins known as enzymes
COMARATIVE BIOCHEMISTRY
3. In all cells,
proteins are
synthesized
from about 20
known amino
acids
COMARATIVE BIOCHEMISTRY
4.Carbohydrate
molecules of cells
consist of 6 carbon
sugars (glucose) and
polymers of these
(cellulose, starch,
glycogen)
COMARATIVE BIOCHEMISTRY
5.All cells obtain energy
from processing
glucose in glycolysis
In most organisms,
oxygen can be used
as an electron
acceptor in the
breakdown of pyruvic
acid to CO2 and water
COMARATIVE BIOCHEMISTRY
6.All cells contain DNA,
a molecule that
carries coded
information controlling
the metabolism of the
cell.
DNA also transmits
the coded information
to new cells
COMARATIVE BIOCHEMISTRY
7. DNA in organisms
determines the
specificity of proteins
through intermediate
compounds such as
mRNA
COMARATIVE BIOCHEMISTRY
8. Structures of
important lipids,
proteins, &
specialized molecules
such as DNA, RNA,
ATP and some coenzymes are similar
COMARATIVE BIOCHEMISTRY
The Genetic
Code is
Universal
AGE OF THE EARTH
AGE OF THE EARTH
AGE OF THE EARTH
• Lord William Thomson Kelvin was the 1st to try to determine the age
of the Earth
• In 1866 he assigned it an absolute age of 400 million years (later
revised his estimate to 15-20 millions yrs.
• Pierre Currie (1903) discovers radioactive decay. Its use provided
geologists with the means to estimate the absolute age of the Earth
• Radiometric dating has been used to date meteorite samples. All
that have struck Earth have been about 4.6 billion yrs
• Moon rocks from the Apollo missions have been dated at 4.53 billion
yrs
• Oldest rock on Earth (from Canadian Shield) is 3.9 billion yrs old.
This is the age where the Earth began to cool & did not undergo
further melting. The Earth is likely 4.6 billion years old.
GEOGRAPHIC DISTRIBUTION
Inhabitants of ocean islands
resemble forms of the nearest
mainland but show some
differences, which suggests
that they have evolved from
mainland migrants
Galapagos Land Iguana
Green Iguana from Panama
PROTECTIVE RESEMBLENCE:
Industrial Melanism
• Shows the effects of
an environmental
change on selection
patterns of birds that
eat peppered moths
• Industrial melanism is
a phrase to describe
the evolutionary
process in which light
colored moths
become dark as a
result of natural
selection
DOMESTICATION & ARTIFICIAL SELECTION
• We can easily breed
animals/plants to
achieve desirable
characteristics
• If we can achieve
these changes over a
a short period of time,
the environment could
cause changes in a
long period of time