Download Evolution Keystone Presentation Part 2

Evolution and
Natural Selection
Review Presentation
for Biology Keystone
Assessment
Created by Joshua Collins
2011
Table of Contents
1) What is Evolution?
2) Natural Selection
3) Evidence for Evolution
4) Evolution in Action
1) What is
Evolution?
2) Natural
Selection
3) Evidence for
Evolution
4) Evolution
in Action
Section 3 of 4:
Evidence for
Evolution
3) Evidence for Evolution
I. Geographic
Distribution
IV. The Fossil
Record
II. Homologous
Anatomy
V. Embryology
III. Vestigial
Structures
VI. DNA and
Genetics
Evidence For Evolution:
I. Geographic Distribution
Geographic
Distribution 
Related native species
are found only where
they could have
migrated on their own.
The distribution of ancient fossils, such as Mesosaurus,
across the continents is a perfect example of this, although
Darwin had no way of explaining how they got there, since
plate tectonics had not yet been discovered!
Evidence For
Evolution:
I. Geographic
Distribution
AFRICA
The island of Madagascar is another great
example of a set of species that naturally
occur nowhere else in the world, for
example, about 100 different species of
lemur, a group of primates that branched
off from earlier monkey-like primates when
Madagascar split off from the African
mainland about 160 million years ago.
Madagascar
• There are thousands of other species
completely unique to this island.
• They are all most closely related to the
species found along the east coast of Africa,
because they share common ancestors.
Evidence For
Evolution:
I. Geographic
Distribution
While Darwin was putting together his theory of evolution by
natural selection, another British naturalist named Alfred Wallace
was doing his own work in the East Indies, where he made some
new discoveries about the species there.
Pacific
Ocean
Borneo
Java
New
Guinea
Alfred Russel
Wallace
Australia
Evidence For
Evolution:
I. Geographic
Distribution
• Wallace saw that the islands of the East Indies were home to two completely
different sets of mammals: monkeys and other placental mammals on the
islands to the northwest, and marsupials to the southeast.
• It was as if these two groups were divided by some invisible barrier that they
could not cross even though the distance was less than 40 km across.
• Other species including many birds were clearly cut off by the line as well.
Borneo
Pacific
Ocean
Java
New
Guinea
Placental
mammals
Australia
Marsupials
Evidence For
Evolution:
I. Geographic
Distribution
The islands on either side of the line made up different
geologic formations divided by a deep channel. The two
groups, therefore, had never been connected.
Even though the climates
were almost identical, the
flora and fauna were
drastically different on
either side of the line
because the species had
evolved in isolation from
each other, just as the
species on Madagascar
had been isolated from the
mainland of Africa.
Borneo
Pacific
Ocean
Java
New
Guinea
Australia
Evidence For
Evolution:
I. Geographic
Distribution
Flightless birds are another great example of evidence based on geographic
distribution, because in most cases, their ancestry can be traced back to
ancient birds who flew to the island from the mainland.
• When birds colonize an
island with no predators,
they often lose the ability
to fly over time because
they don’t need to fly to
survive.
• Examples: kiwi, penguin,
& the dodo bird.
Evidence For Evolution:
II. Homologous Anatomy
Homologous
Anatomy
Traits that are similar
between species because
they originate with a
common ancestor who
had the same trait.
• The example above compares the internal structure of a human
arm with the forelimb of a whale.
• Although the shape of each bone is different, each bone in the
human arm has a corresponding match in the whale.
Evidence For
Evolution:
II. Homologous
Anatomy
• In fact, every one of these animals has the same basic forelimb structure:
a shoulder blade bone, a single humerus, two forearm bones, followed by
many wrist bones and digits.
• They all trace back to a common ancestor, the earliest tetrapods, which
had this basic layout, almost as a template.
It’s just been
gradually
modified for
different uses
over millions
of years.
Evidence For
Evolution:
II. Homologous
Anatomy
Looking at these feet up close gives you an idea of how
similar they really are, bone for bone.
Human
(hand)
Dog
Pig
Cow
Tapir Horse
r — Radius, u — Ulna, a — Scaphoid, b — Lunare, c — Triquetrum,
d — Trapezium, e — Trapezoid, f — Capitatum, g — Hamatum, p — Pisiforme
Evidence For
Evolution:
II. Homologous
Anatomy
In the case of the horse,
the entire middle digit
which has been modified
into the lower part of the
leg, while the other digits
became smaller and
smaller until they are
completely gone.
Human
Tapir
Horse
A horse’s hoof corresponds to
our middle fingernail while
the knee actually matches up
to our wrist bones.
Evidence For
Evolution:
II. Homologous
Anatomy
Remember, homologous traits are adaptations that are
similar between species because both species share an
ancestor with the adaptation. For example, the following
species all have wings, because they evolved from an
earlier bird ancestor with wings.
In this case, the three
species have diverged
from each other for long
enough that their wings
have gradually taken on
different uses.
Evidence For
Evolution:
II. Homologous
Anatomy
Bird wing
• Not all similarities between
species are homologous, however,
because not all traits are inherited
from a shared ancestor.
• Although both birds and bats use
wings to fly, when you look at
their anatomy, it’s obvious that
their wings are completely
different.
Bat wing
• The similarity is not due to
common ancestry. Rather, birds
and bats have undergone
convergent evolution.
Evidence For
Evolution:
II. Homologous
Anatomy
Bird wing
Convergent
Evolution 
• When two species evolve a
similar adaptation not because of
common ancestry but because
they have become adapted to a
similar environment, or use the
trait for a similar function.
• In other words, they have both
“converged” on the same
adaptation in their own way.
Bat wing
Birds and bats have both evolved wings
because they both use them to fly.
Rather than “homology”, this is called an
“analogous trait” or simply, an analogy.
Evidence For
Evolution:
II. Homologous
Anatomy
Diagram 1 below illustrates how the eagle and the penguin
evolved their wings from earlier birds. Diagram 2 shows
how birds and bats evolved their wings separately.
species A
species B
species A
species B
adaptation
Homologous
traits
adaptation
Diagram 1
adaptation
Analogous
traits
Diagram 2
Evidence For
Evolution:
II. Homologous
Anatomy
Four legs: Homology or Analogy?
Homology:
This is a
homologous trait
because all of
these species
evolved from the
earliest tetrapod,
which also had
four legs.
Evidence For
Evolution:
II. Homologous
Anatomy
Two eyes: Homology or Analogy?
Homology:
This is a homologous
trait because all
vertebrates have two
eyes.
This allows some
animals to see almost
360°, and it allows
humans to see in 3D.
Evidence For
Evolution:
II. Homologous
Anatomy
Protruding eyes:
Homology or Analogy?
Analogy:
This is an example of
convergent evolution
because not all reptiles and
amphibians have this trait.
Frogs and alligators have
evolved the same
adaptation independently,
but for similar use: to see
above the water’s surface.
Evidence For
Evolution:
II. Homologous
Anatomy
Analogy:
Many placental mammal
species have corresponding
marsupial species, which
occupy the same ecological
niche on other continents.
They are not related, however,
and their similarities are due to
similar environments and ways
of life. This is, once again,
convergent evolution at work.
Marsupials
Placentals
All of the placental mammals are more closely related
to each other than to any marsupial, and vice versa.
Evidence For
Evolution:
II. Homologous
Anatomy
Evidence for evolution:
Homologous
traits
Both homologous and
analogous traits are
excellent evidence for
evolution, because they
show how different
species are related and
how they evolved their
adaptations for survival.
Analogous
traits
Evidence For Evolution:
III. Vestigial Structures
Vestigial Structures
Physical remnants of organs that once helped a
species’ ancestors survive, but are no longer useful.
• Vestigial structures tend to be very small,
because they are not needed for survival.
Hence, they are only “vestiges” of what they
once were.
• If a species has an anatomical structure that
appears to be out of place, many times it is
vestigial.
• The human appendix is a good example of a
“vestige” of an earlier digestive organ that
helped our ancestors process plant material.
Evidence For
Evolution:
III. Vestigial
Structures
Other human examples include
the tailbone and wisdom teeth.
Remnant of earlier
primate ancestors
with tails
Leftover from
our ancestors
with larger jaws
This is why wisdom teeth are so commonly removed.
Modern humans’ jaws tend to be too small, so the teeth get
impacted. Some people never even develop wisdom teeth.
Evidence For
Evolution:
III. Vestigial
Structures
The wings on flightless birds are vestigial structures because they
have shrunken over thousands of generations to the point where
they can no longer be used for flight.
Why did the wings
“shrink” over time?
Often, flightless birds are found on
islands where their ancestors landed
millions of years before. On an island
with no predators, wings are not
really needed for survival.
In some cases, e.g. penguins,
their smaller wings have since
become useful in other ways.
Evidence For
Evolution:
III. Vestigial
Structures
Though whales spend their entire lives underwater and have no hind limbs,
they still have tiny leg bones and remains of a pelvis, which have shrunken
to the point where they’re not even attached to the rest of the skeleton.
In other words, whales have leg bones.
What possible explanation makes sense
unless they gradually evolved from earlier
ancestors who had legs and lived on land?
Evidence For
Evolution:
III. Vestigial
Structures
Rather than physical structures,
some vestigial traits come in the
form of reactions or behaviors.
When you get goosebumps
because you are startled or get a
chill, your body is reacting in the
same way as this cat.
This reaction no longer serves any purpose in
human beings but earlier mammal ancestors, as
well as those still around, use it to puff up their fur
for warmth, or to intimidate would-be predators.
Evidence For
Evolution:
III. Vestigial
Structures
Here are a couple more examples:
Similar to whales, pythons and
boa constrictors have remnants
of pelvic bones and legs. In this
case, however, they are actually
visible externally.
Blind cave fish
Pelvic spurs
on a python
Certain fish species
which have lived in
caves for thousands of
years have evolved to
have no eyes, since they
are useless in the dark.
Evidence For
Evolution:
III. Vestigial
Structures
•
Even more tellingly, most species,
including humans have huge
sections of so-called “junk DNA”
which seem to be completely
non-functional.
•
Much of this “useless” genetic material is
vestigial. In other words, it used to code for
important traits in our ancestors, but is no
longer needed.
•
This vestigial DNA has essentially become
“deactivated” through genetic mutations
over the course of millions of years, and is
now just taking up space on the genome.
Evidence For Evolution:
IV. The Fossil Record
The Fossil Record
• A physical history of the life on
Earth in the form of fossils buried
within chronologically oriented
layers of sedimentary rock.
• Shows gradual progression,
including transitional species.
Tiktaalik
Discovered in 2004,
Tiktaalik is a fossil specimen
that shows the transition
between ancient fish and
the first land-dwelling
amphibians, around 380
million years ago.
Evidence For
Evolution:
IV. The Fossil
Record
The fossil record of
the modern horse is
a great example of
the continuous
progression that
shows gradual
change over
millions of years.
Notice how the toes
gradually get smaller
and smaller, leaving
only the middle toe,
which becomes the
foot and hoof of the
modern horse.
Evidence For
Evolution:
IV. The Fossil
Record
•
The evolution of fourlimbed organisms, or
tetrapods, shows a
similar progression.
•
There are no giant
leaps; only tiny, gradual
incremental changes
over millions of years.
•
New transitional
fossils, sometimes
called “missing links,”
are continually being
discovered.
Evidence For
Evolution:
IV. The Fossil
Record
Ambulocetus
(50 million years ago)
Fossil evidence has
demonstrated how
whales have evolved
from land mammals
who walked on four
legs.
Rodhocetus
(47 million years ago)
Evidence For
Evolution:
IV. The Fossil
Record
Ancient land-dwelling
ancestors
• Once again, there is gradual
progression in the fossil
record, and new fossils are
being discovered all the time.
• The gradual change can even
be seen in the evolution of
the blowhole.
Modern baleen whales
Evidence For
Evolution:
IV. The Fossil
Record
Eupodophis
Archaeopteryx
(150 million years ago)
Transition between
dinosaurs and birds
(92 mill.)
Transition between
lizards and the
earliest snakes
Evidence For
Evolution:
IV. The Fossil
Record
Australopithecus afarensis
Dimetrodon
(265 mill.)
Transition between
reptiles and early
mammals
(3.2 mill.)
Transition between
primitive ape-like
hominids and more
modern humans
Evidence For
Evolution:
IV. The Fossil
Record
Thousands of hominid specimens have been
discovered in the past century, allowing
scientists to piece
together the
hominid family
tree, extending
back about 6
million years to
our ape-like
ancestors.
Every newly discovered
species is a transition
between its ancestors
and descendants on the
tree of life.
Evidence For
Evolution:
IV. The Fossil
Record
Duck-billed platypus
Some modern species,
such as the platypus still
retain certain primitive
traits, that link them to
these early transitional
“missing links.”
The platypus belongs to a group of primitive mammals called
monotremes. This group branched off from reptiles very early,
and so these species still lay eggs like their reptile ancestors.
Evidence For
Evolution:
IV. The Fossil
Record
• Similarly, mudskippers
are amphibious fish
which are able to gulp air
and walk on land using
their strong pectoral fins.
• Not really a “living fossil”
because the species
evolved relatively
recently
Mudskipper
• Still represents a modern
look at the transition
between sea and land,
when the earliest
amphibians evolved
Evidence For Evolution:
V. Embryology
Embryology
Very close similarities in
early developmental stages
of related species
1 cm
Human embryo
5 weeks after
conception
Evidence For
Evolution:
V. Embryology
Can you guess what type of animal this is?
Evidence For
Evolution:
V. Embryology
Can you guess what type of animal this is?
Turtle embryo
See the
developing
shell?
Evidence For
Evolution:
V. Embryology
Newly forming vertebrate embryos all look very similar so it’s difficult
to tell what animal you’re looking at in the early stages of development.
All vertebrates start
out almost the same
because they all share
a common ancestor
which was much more
primitive.
Turtle embryo
• All vertebrates embryos start out with a tail and tiny neck slits resembling gills.
This includes humans!
• In land-dwelling groups such as mammals and reptiles, these slits disappear as
the embryo develops, eventually becoming parts of the throat and mouth.
• In humans, the tail is absorbed into the growing body and remains as the
tailbone.
Evidence For
Evolution:
V. Embryology
early development
(all very similar)
middle stage
embryo
(starting to
differentiate)
fetal stage
(identifiable as
separate species)
Evidence For
Evolution:
V. Embryology
Notice how more
closely related
species tend to
resemble each
other further along
in development.
Click here to play “Which Embryo is Human?”
Evidence For
Evolution:
V. Embryology
Bottle-nosed dolphin
Human
Both embryos at about 5 weeks gestation!
Evidence For
Evolution:
V. Embryology
Bottle-nosed dolphin
Notice the
beginnings of hind
leg buds which
form early on and
disappear later on
in development.
Evidence For Evolution:
VI. DNA and Genetics
DNA
• Genetic code shared by
all living things on Earth
• Allows us to look at
different species at the
molecular level and
compare their genes.
• Shows conclusively that
all living things are
related; it’s just a matter
of degree.
Evidence For
Evolution:
VI. DNA and
Genetics
• Comparing our DNA allows us to determine
which species are our closest relatives.
• Humans and chimpanzees’ DNA are roughly 96%
identical.
human
This evidence indicates
that both chimps and
humans received their
identical genetic material
from a common ancestor
who lived about 6 million
years ago.
Evidence For
Evolution:
VI. DNA and
Genetics
apes
“Great Apes”
human
hominids
These primate groups are
determined by how
much homologous DNA
they have in common.
Evidence For
Evolution:
VI. DNA and
Genetics
•
DNA evidence is some of the strongest evidence for evolution
and the common ancestry of all living things on Earth.
•
It allows us to confirm at the molecular level the extent to
which species are related AND estimate how long ago two
species probably diverged from their common ancestor.
• Molecular DNA evidence
shows that humans and
chimpanzees diverged from
one another between 5 and
7 million years ago.
• That common ancestor
diverged from the gorilla
family line even earlier, and
so on down the family tree.
Primatologist, Jane
Goodall and one of
her chimp friends
Evidence For
Evolution:
VI. DNA and
Genetics
•
All of the Great Apes
have their DNA organized
into 24 chromosome
pairs, whereas humans
have only have 23 pairs.
•
If humans share a
common ancestor with all
the other Great Apes, we
should all have the same
number of chromosome
pairs because no one
could survive if a whole
section of DNA just
disappeared!
How is this possible?
(24 pairs)
(23 pairs)
Evidence For
Evolution:
VI. DNA and
Genetics
If one chromosome pair
wasn’t just lost, then what
could have happened to it?
What if two of the earlier ape
chromosomes somehow got
“stuck”, or fused, together
during cell division at some
point in the distant past?
(24 pairs)
(23 pairs)
Is there any way to verify this?
Evidence For
Evolution:
VI. DNA and
Genetics
Actually, it has been verified.
• By examining the genes found on
the ape chromosomes, scientists
have found two ape chromosomes
that contain the same genes that
appear on ONE of our human
chromosomes.
• So it’s been conclusively
demonstrated that they did get
“stuck” together, and all modern
humans have inherited that fused
chromosome.
(24 pairs)
(23 pairs)
Evidence For
Evolution:
VI. DNA and
Genetics
• This image shows the genes
that match up between
human and chimp DNA.
• Note the two chimp
chromosomes that match up
to our own chromosome #2.
This chart also shows
how different sections of
DNA have inverted
themselves at multiples
times in the past. This is
one type of mutation.
Evidence For
Evolution:
Click the image above to see biology
professor Kenneth Miller explain the
“Case of the Missing Chromosome”.
Orangutan
Gorilla
Chimp
This is extremely conclusive evidence
of our common ancestry with all the
other apes.
Human
VI. DNA and
Genetics
1) What is
Evolution?
2) Natural
Selection
3) Evidence for
Evolution
Section 4 of 4:
Evolution
in Action
4) Evolution
in Action
4) Evolution in Action
Usually, the process of evolution takes place
so slowly that we can’t see it happening.
In selective breeding of livestock and hybridization of crops, humans
have sped up and exaggerated this basic process so that we can actually
observe the allele frequencies changing over shorter times.
There are numerous examples, however, in which a
species evolves rapidly enough on their own that we
can see evolution in action.
This usually happens because of one or both of the following:
1) A species reproduces
very quickly so that
numerous generations
pass in a short time.
2) Selection pressure is
very great.
Bacteria reproduce extremely quickly, and many
can double their population in under an hour.
Bacteria can quickly evolve to be resistant to
antibiotics if the drugs are not administered
properly or for the entire duration of the
infection.
If any bacteria are not fully wiped out by
the antibiotics, the more resistant ones
that remain will continue to reproduce.
An example of rapid evolution due to very high selection
pressure is taking place among African elephants.
As prized sources of ivory,
they are being hunted closer
and closer to extinction
mainly for their tusks.
• Since the elephants with the largest tusks are being hunted
most, there is a heightened selection pressure (in this case,
humans) that is wiping out large-tusked elephants.
• The remaining population has higher frequency of smallertusked elephants, and some with no tusks at all!
• So overall, it appears that elephant tusks are shrinking.
Human evolution in action
• Sickle-cell anemia is a genetic disorder in
which the blood cells take on a shriveled
sickle shape.
• The disease can be life-threatening and
generally tends to reduce life expectancy
significantly.
• The disease is treatable. In America, it
affects about 90,000 people, while there
are over 2 million genetic carriers who
have one recessive sickle-cell allele, but
do not have the actual disease.
It has long been known that the frequency of the disease
widely varies between certain ethnicities, and occurs at a
much higher ratio among those of African descent.
It appears that the
frequency tends to
correspond to people
originating in more
tropical climates.
What might explain this
curious connection?
Incidence of the
sickle-cell trait
in Africa
Distribution of
Malaria
Incidence of the
sickle-cell trait
in Africa
In 1954, a scientist named Tony Allison found the clue when he
realized how closely the frequency of sickle-cell anemia matched
the distribution of malaria in Africa.
• To explain the extremely high frequencies of the sickle-cell allele,
Dr. Allison figured that the genotypes leading to the disease must
be giving some sort of survival advantage to those who have the
allele (including carriers of the disease).
• Since the sickle-cell allele seemed to be geographically linked to the
distribution of malaria, he hypothesized that the sickle-cell gene
must somehow increase the carrier’s resistance to malaria.
With Watson and Crick’s recent
discovery of the structure of
DNA, new molecular evidence
soon confirmed Dr. Allison’s
hypothesis.
• Since malaria is a much bigger threat to survival than sickle-cell
anemia, the sickle-cell trait had become prevalent in the areas
where its benefits outweighed the negative effects.
• Dr. Allison was able to show that the same mutation that led to the
sickle-cell trait had occurred at several points in the past in different
locations. But it only became prevalent in areas where malaria was
widespread.
This was an excellent
confirmation of the
process of evolution
occurring in real-time
in ways that directly
affect humans.
Table of Contents
1) What is Evolution?
2) Natural Selection
3) Evidence for Evolution
4) Evolution in Action