Evidence for Evolution
http://humans4.beyondgenes.com/
http://faculty.southwest.tn.edu/rburkett/GB%20Properties%20of%20Life.htm
Fossilization
Snowmelt from the mountains
washes sediments into lakes and
shallow seas.
Fossilization
Overtime, these sediments pile
up and compress the older
sediments below into rock.
Fossilization
These layers are called rock strata.
Fossilization
A few organisms that die in the
sediment become fossilized.
Fossilization
Fossils are the preserved remains
or markings left by organisms that
lived in the past.
Fossilization
Depending on the process, it could take
anywhere from tens of thousands to
millions of years for fossils to form.
The Fossil Record
Thus the oldest
layer and any
fossils it contains
is at the bottom; and the youngest
layer and fossils
are at the top.
Youngest
Oldest
The Fossil Record
The fossil record shows that life
became more complex over time.
Simple
Complex
Youngest
Oldest
The Fossil Record
The positions of the fossils in the rock
strata can reveal their relative age.
Youngest
Oldest
The Fossil Record
The fossil record is this chronological
collection of life’s remains in rock layers,
recorded during the passage of time.
Youngest
Oldest
Why are marine fossils found on mountain tops?
When land masses collide, mountains may form.
The energy from these collisions can bend
and fold rock.
Mountain building can
force marine fossils from
the sea floor high up
onto mountain peaks.
Burgess Shale, B.C., Canada
Anomalocaris canadensis
If the folding is severe enough, the fossil
record may appear to be upside down.
Oldest
Youngest
The fossil record provides evidence of Earth’s
changing life.
The oldest evidence of life consists of
chemical traces in rocks from Greenland that
are 3.8 billion years old.
Rocks of Greenland’s Akila island.
http://www.sciencedaily.com/releases/2006/07/060721090947.htm
Fossils of prokaryotes (bacteria and
archaea) have been found in rocks
about 3.5 billion years in age.
Cyanobacteria
The fossil record provides evidence of Earth’s
changing life.
Fossils of prokaryotes
(bacteria and archaea) have
been found in rocks about
3.5 billion years in age.
Stromatolites
“Bacteria poop”
These data fit with the molecular and cellular
evidence that prokaryotes are the oldest form of life.
Photosynthetic bacteria
Fossils in younger layers of rock record the evolution
of various groups of eukaryotic organisms
Fossils of species that become extinct—species that
no longer exist—help scientists reconstruct the past.
Paleontologists (scientists who study fossils) have
discovered fossils of many ancestral life forms that
link past and present.
For example, fossil evidence supports the hypothesis
that whales, which have no hind limbs, evolved from
land-dwelling ancestors that had four limbs.
Paleontologists digging in Egypt and Pakistan have
identified ancient whales that had hind limb bones.
Basilosaurus, which lived about 40 million years ago
is one of these early whales.
Even larger leg bones are found in fossils of older
whale species that may have split their time
between living on land and in water.
Ambulocetus natans
These examples
of transitional
fossils show the
evolution of the
whale over
millions of years.
In the early 1900’s, whalers documented many cases of
reduced hind-limbs in humpback and sperm whales.
tibia
Femur
metatarsal
tarsus
Pelvis
The study of embryo development has also
provided evidence supporting evolution.

For example, these fetal
structures in whales that
disappear before birth:





Hind limb bud
Body Hair
Rudimentary ear pinnae*
Brain olfactory lobes
Teeth on baleen whales.
Beluga Whale Embryo
*Outer ear (Carried as rare atavisms in all whales, rudimentary in belugas)
Expected ≠ Observed
When Darwin set sail on the Beagle, he
believed a recent world-wide flood killed all
but a handful of each species.
Based on his readings
and discoveries during
his 5-year voyage,
however, Darwin began
to question this account.
Sediment Sorting
He wondered why the composition of thousands of
feet of rock layers he observed did not conform to
what one would expect from a world-wide flood.
Observed
Expected (flood)
Shale
Disconformity
Slate
Conglomerate
Shale
Sandstone
Fossil Oganization
Darwin was also puzzled as to why fossils were sorted out
by complexity, rather than laid down indiscriminately as
would be expected if a world-wide flood occurred.
Expected (flood)
Youngest
Oldest
Observed
Geographic Distribution
Darwin also wondered why there was an uneven
distribution of species around the world.
Geographic Distribution
For example, Australia is home to so many kinds of
pouched animals (marsupials)—such as koalas,
kangaroos, and wombats—while very few placental
animals—such as deer and squirrels—live there.
Koala
Kangaroo
Wombat
Geographic Distribution
Darwin discovered that the koala’s diet is
restricted to a few subspecies of eucalyptus.
Eucalyptus is a poor
nutrient food, which
accounts for the koala’s
arboreal lifestyle, low
metabolic rate, and low
energy requirements.
Geographic Distribution
According to the world-wide
flood account at the time,
only a few koala’s survived
the flood and were deposited
on top of Mt. Ararat in Turkey
about 4,500 years ago.
Mt. Ararat
Geographic Distribution
Darwin wondered how so few koalas could travel over
9,000 miles from Mt. Ararat to Australia, eating a
conventional trail of long-disappeared eucalyptus,
without leaving a trail of koala fossils behind.
Homologous Structures
Darwin also pointed to certain similarities in structure
among species as clues to their evolutionary history.
For example, the forelimbs of all mammals consists
of the same skeletal parts, even though the
functions of these forelimbs differ.
Homologous Structures
Such similar structures in species sharing a common
ancestor are called homologous structures.
Homologous Structures
Darwin described evolution as a remodeling process.
Structures that originally functioned one way in ancestral
species become modified as they take on new functions.
Homologous Structures
This idea is what Darwin meant by “descent with
modification.”
Less than a perfect design
Darwin noted limitations of this retrofitting are
evident in structures that are less than perfect.
For Example:
Why is the giant panda's
'thumb' made of an
altered wristbone (the
radial sesamoid), rather
than the normal digit?
Sub-optimal design
Why are vertebrate eyes wired “backwards,” thus creating a
blind spot and increasing susceptibility for detached retinas?
Sub-optimal design
Why don’t tarsiers have a reflective membrane (tapetum lucidum)
in the back of their eyes like cats do for seeing in the dark?
No tapetum
membrane
results in
oversized eyes.
Presence of the
tapetum allows
eyes to be much
smaller.
Knee and Back Problems
Why do humans have knee and back problems? Is it
because the human spine and knee joints were derived from
ancestral structures that supported four-legged mammals—
not two legged mammals that walked upright.
Speaking of walking upright, a single mutation
in a gene related to balance prevents these
individuals from walking on two legs. To get
around, they must walk on all fours.
Vestigial Structures
Darwin also pointed to vestigial structures, which are
homologous structures that survive as degenerate, imperfect
versions of what they should be.
Calabar poto
(a primate)
Nictitating
membrane
Human
(primate)
Functioning
Nonfunctioning
Eagle
Wings for flight
Functioning
Nonfunctioning
Kiwi
bird
Vestigial Structures
Often, vestigial structures are reduced in size.
Appendix
(Digestion
of plant
material)
Canine
teeth
Vestigial Structures
Some skinks have one or
two pairs of legs that are
not used for walking.
There are many birds with wings
that can’t use them for their
original function—to fly.
Cassowary
Kasner’s Skink
Penguin
Kakapo parrot
Cape Skink
Ostrich
Vestigial Structures
Can you figure out what the vestigial structure is?
Cave
salamander
Weevle
(apertocyclus)
Dandelion
The eyes, which contain
retinas and lenses, are
covered with a
nonfunctional eyelid.
The dandelion has a
flower that is not
needed, since it
reproduces asexually.
Dandelions even
produce pollen,
which are not
needed in asexual
reproduction.
Fused wing covers
permanently enclose
fully developed wings.
Atavistic Structures
Atavisms are traits of distant ancestors that reappear in
the modern day. In order for the trait to be an atavism,
an organism's parents can't have the trait, and neither
can recent ancestors.
Ancient
horse
(miohippus)
25 -32 mya
Modern
horse
Atavistic Structures
There are many fossils of snakes showing leg structures.
100 million year
old snake fossil
Pachyrhachis
problematicus
Occasionally
modern snakes are
found with one or
two hind legs
bearing claws.
Hind legs on snakes should not to be confused with snake penises
Atavistic Structures
And in 2006, Japanese fishermen caught a
bottlenose dolphin that had atavistic hind limbs.
Embryo of a
spotted dolphin
at 24 days
Hind limb bud
Atavistic structures in humans
In rare cases humans are
born with tails.
Occasionally a person has
a tail that can be wiggled.
Atavistic structures in humans
In the embryo stage,
all humans start out
with a tail. As the
embryo grows, the tail
disappears.
Some tails have additional
vertebrae with attached muscles
and nerves. This is why some
people can wiggle their tails.
Normal human
coccyx (tail bone)
Tail
Human Embryo
Human tail
vertebrae
Atavistic Structures
1 person in 25 usually has an extra nipple that runs down
the embryonic milk line. In most cases the extra nipples
look like blemishes or moles, but in some cases can be
well developed and actually lactate (produce milk).
Supernumerary Celebrities: Mark
Wahlberg, Joanna Krupa, Lilly
Allen, Harry Styles (2), Tilda
Swinton, Carrie Underwood,
Both males and
females can be
born with this
condition. If a
male baby is
born with too
much estrogen,
it will produce
milk from its
nipples.
In humans, as
many as eight
nipples can
appear along
the milk line as
shown above.
Is hypertrichosis an atavistic structure?
Answer: Unknown
Jesus 'Chuy' Aceves
(isolated to X chromosome)
Lilia Aceves
Larry Gomez
Julia Pastrana
Fedor Jefticheff
“JoJo”
Fedor Jefticheff
“Lionel”
Phylogenetic relationships
Among siblings, the
DNA and protein
sequences are very
similar.
However, the sequences of
unrelated individuals of
the same species show
more differences.
Phylogenetic relationships
This idea of molecular
comparison extends to
studying relationships
between species.
If two species have
genes and proteins
with sequences that
match closely,
biologists conclude that
the sequences must
have been inherited
from a relatively recent
common ancestor.
Dalmation
Dingo
1 mya
Recent
common
ancestor
Grey Wolf
Phylogenetic relationships
In contrast, the greater
number of differences in
DNA and protein
sequences between
species…
the less likely they
share as close a
common ancestor.
Dalmation
Dingo
Cat
1 mya
Recent
common
ancestor
Grey Wolf
Distant
common
ancestor
45 mya
Hesperocyon
Chromosomes
Over time, the number
of chromosomes may
change as new species
emerge.
Chromosome Count
38
For example: house
cats, tigers and lions
have 38 chromosomes;
dogs, dingos, coyotes
and wolves have 78
chromosomes.
This is just one of the
many reasons why dogs
can’t mate with cats.
http://en.wikipedia.org/wiki/List_of_number_of_chromosomes_of_various_organism
s
78
Molecular biology
The hemoglobin molecule
provides an excellent example
of biochemical evidence for
evolutionary relationships.
Hemoglobin
Hemoglobin is the protein that
carries oxygen in the blood.
Red blood cells
The human hemoglobin
protein consists of 287
amino acids.
4 amino acids
Molecular biology
Assume a common ancestor
has the following hemoglobin
amino acid sequence:
One million generations later,
some of its descendents inherit a
version with a mutation (yellow).
As the years pass by, more and
more mutations appear in the
heritable sequences.
Thus, the longer the sequence is
passed down to descendents, the
greater the number of mutations
that will accumulate.
Val-His-Thr-Pro-Glu-Lys-Ser
Val-His-Gly-Pro-Glu-Lys-Ser
Val-His-Gly-Pro-Glu-Arg-Ser
Cys-His-Phe-Pro-Glu-Arg-Ser
Note that this amino acid
position mutated twice.
Molecular biology
Not all DNA accumulates mutations at the same rate.
For example, if the section of
DNA is important to protein
synthesis, then we can expect
very few mutations to occur
over time.
If the section of DNA is not
involved in protein coding,
then we can expect a greater
number of mutations over the
same period of time.
A T C C T T T G A C T
A T C C T T T G A C T
10 million years
10 million years
1 mutation
A T C C T A T G A C T
3 mutations
A T T C T A T G A C C
Molecular biology
This graph shows how many of the 287 amino acids in human hemoglobin differ when compared to the hemoglobin of other organisms.
The average mutation rate for a given gene in all creatures
is about 1 x 10-6 mutations per gene per generation (or one
mutation / gene / million generations on average).
As you can see, the gorilla’s hemoglobin sequence when
compared to humans, differs in only one amino acid,
inferring a close relationship.
The mutation rate for humans is estimated to be about
2.2 x 10-9 mutations per base pair per year. With about
6.3 billion base pairs per genome, that works out to
around 14 transmissible mutations per year per person.
On the other hand, there are 125 differences when
compared to the lamprey, indicating a very distant
relationship.
http://www.bio.miami.edu/dana/106/106F05_4.html
Phylogenetic trees like the one shown below are developed by
combining morphological, geographical and molecular data.
http://geology.fullerton.edu/whenderson/Fal201L2005/DogEvolution/Dog%20Website/EVOLUTION.HTML
The Ends