Chapters 10
Principles of Evolution
What in the world is it and what is that pink thing?
Write down what you think it is and what the pink thing is for.
This is a star-nosed mole which lives underground.
The 22 fingerlike rays are used for finding food and its claws are
used for burrowing. It’s eyes are basically useless therefore its
hearing is sharp
What is Evolution?
What comes to mind when you hear or read the term “evolution”?
• Evolution is the gradual biological
change in a species over time.
• It is based on the concept that
modern organisms have
descended from other organisms
Human Evolution
• 225 million years ago, the first mammal evolved
• 65 million years ago, the first primate evolved (and the
dinosaurs went extinct)
• 6 million years ago, the first hominid evolved (man like
primate)
• 2 million years ago, the species Homo evolved
• Homo sapiens ~ 50,000 years ago.
This concept of Evolution, that organisms shared a
common ancestry didn’t happen over night.
It took many people and many years to form this theory
1. Carolus Linnaeus (1700’s)
a. Proposed a system of organization of all
living things based on physical similarities
b. Proposed that organisms might have arisen
from crossing between two similar species
c. Species – a group of organisms that are able
to reproduce fertile offspring.
- A mustang and a miniature horse can mate and produce a
pony that can eventually reproduce because the two are from
the same species (Equus caballus) .
- A horse and a donkey (Equus africanus) could reproduce but
the mule will never be able to reproduce.
What would you do if the most important things you
needed were up high and you were alone, without
anything to climb on?
2. Jean-Baptiste Lamarck (1809)
a. Believe in decent from common ancestry
b. Proposed that organisms have a tendency
towards perfection and needed to change
to better fit in with their environment.
c. Through selective use and disuse of organs,
organisms acquired or lost certain traits
during their lifetime.
d. By passing on these acquired traits to their
offspring, a species can change over time.
Fossil evidence shows that the ancestors of the modern
giraffe originally had shorter necks.
These shorter necked giraffes had eaten all the food on
the lower branches & needed to get to the food higher
up.
By stretching their necks, to get to the higher up leaves,
after many generations, the giraffes acquired the long
neck trait.
The following generations would all inherit the acquired
trait.
What parts of Lamarck’s theory do you agree
or disagree with?
1. A need to change (Tendency towards perfection)
2. Use and disuse (if you use it, it develops, if not, it goes
away)
3. Acquired traits (we can acquire traits in our lifetime)
4. Inheritance of acquired traits (passing on things we
acquire or develop in our lifetime)
How would Lamarck have explained how the sandpiper got its shape?
In 8th grade, you studied Earth Science. Here are a few
review questions for you.
1. How old is the earth?
4.6 Billion years old
2. What was the earth like when it first formed?
It was molten, then solidified, then water forms. It was HOT!!
3. When did life begin on earth?
3.6 billion years
4. Where the 7 continents always in the same place?
Plate Tectonics and continental drift. The continents were all one big
mass and then moved due to the movement of the mantel below.
5. Does the earth change today?
Volcanoes, earthquakes, hurricanes, global warming, ice ages,
erosion, …
Evidence and concepts that helped shaped the concept
of evolution
a) Fossil (traces of organisms that existed in the
past) evidence showed that organisms can go
extinct.
b) Catastrophism – natural disasters like floods,
volcanoes, asteroids… have happened and
could cause mass extinctions of organisms.
Like what happened to the dinosaurs!!
Ice Age
Giant
Asteroid
Did this happen all of a sudden?
c. Gradualism
•
The earth is in layers that formed very slowly &
has been altered over time by forces of nature.
What does the image on the right tell
you about how the earth
changed?
d. Uniformitarianism
• The events of earth’s
past are happening
today
History of Charles Darwin
• 2/12/1809 – 1882
• Very wealthy - Married 1st cousin
• Studied medicine & theology but ended up
being a naturalist.
Starting in 1831, he took a 5 year voyage
on the HMS Beagle as the ship’s
naturalist, from England, around South
America, to the Galapagos Islands,
below Australia and and Africa, back to
SA and then to England
Galapagos Is
December 1831 - expedition leaves Plymouth
Crosses the Bay of Biscay and meets rough seas Darwin is seasick
Unable to land at Madeira as the tides are against
them
Unable to land at Tenerife as the islanders fear
that disease has been carried from Britain
Crosses the Atlantic Ocean to Brazil, via the Cap
Verde Islands and the equator
February 1832 - lands at Bahia (Salvador) in
Brazil, where Darwin collects botanical specimens
and comes across slavery for the first time
On to Rio de Janeiro where Darwin spends two
months making observations. He collects 68 beetles
in one day!
Next stop - Tierra del Fuego, and three natives
and a Christian missionary are left behind to work
with the islanders
On to the Falkland Islands where Darwin
observes very simple tiny plant-like sea creatures
HMS Beagle
June 1834 - the Beagle sails round the southern
point of South America, in the stormy seas of the
Straits of Magellan
On to the island of Chiloe and the Chonos group
of islands, where Darwin observes active volcanoes
February 1835 - at Valdivia, Darwin experiences
an earthquake, and visits nearby Concepcion where
he finds the town almost destroyed by the
earthquake
September 1835 - the Beagle arrives at the
Galapagos Islands, where Darwin collects some of
his most important specimens, the finches which can
only be found on these islands
January 1836 - the expedition reaches Australia
April 1836 - Darwin observes an atoll, a coral reef
around a lagoon, in the Keeling and Cocos Islands
The expedition goes round the southern tip of
Africa, via the stormy Cape of Good Hope, and
crosses the Atlantic to complete work in Brazil
October 1836 - the Beagle arrives back at
Falmouth and Darwin is reunited with his family
The Galapagos Islands
1000km west of S. America – Volcanic chain
of Islands
– Low islands were hot, dry & basically void of
life.
– Higher elevations islands had a lot of rainfall
& therefore more variety of life
• Saw much variations amongst inhabitants
of the different islands.
– Unique land tortoises, plants, birds, marine
iguana...
– Species differed from island to island,
especially the tortoise shells & the “little
brown birds” (finches)
Could these all have come from one common
ancestor and evolve to be better suited or
adapted to their particular environment on the
island?
• Darwin was
extremely seasick
throughout the
voyage!
• Published book: On
the Origin of Species
in 1858
How could Darwin have used some of the
concepts from earlier scientists to develop his
theory of evolution by natural selection?
1. Fossils
– Shows that organisms from the past are
similar to organisms of today
– Organisms have gone extinct
2. The earth is old, not just a few thousand
years old
– If the earth is at least 1 million years old,
there is plenty of time for a species to
change
– It’s really 4.6 million years old.
2. Uniformitarianism
– The events of earth’s past are happening
today
– He can see that the earth gets changed by
such events like earthquakes, volcanoes,
fires…
3. Gradualism
– Darwin saw the layers of rocks on exposed
cliffs along with the fossils within these layers
4. Catastrophism
– Though Darwin would not have known what
happened to the dinosaurs, he knew that they
existed at one time & were now extinct.
– Questioned why organisms would go extinct
Suppose that when Apple came out with the new
iPhone 6 and they only issued 5 new phones to each
store. What do you think would have happened?
Thomas Malthus (1798) stated that
whenever a population gets too large,
there are limited resources available to
them.
Sooner or later, there will not be
enough food, space, fresh water …
War, famine & disease are the only forces
to keep the population size from
outdistancing food supply
Darwin questioned that if organisms produce
far more offspring than can survive, what
factors determine which ones survive and
reproduce?
What was the purpose of crossing a horse with
a donkey to get mule?
• The horse is large and can carry a heavy load over
long distance but it isn’t very sure footed.
• The donkey is small but very sure footed and can
walk on very narrow paths.
– When the two are crossed hopefully the mule will be
mid-sized and sure footed.
– Sometimes though, they ended up with a small, thin
ankled mule.
• This is artificial selection
– Process where humans change a species by breeding it
for certain traits.
• Darwin asked himself how nature goes about
selecting which traits are the most desirable.
Darwin puts it all together
1. Natural Variations
Inherited variations/differences exists between
organisms w/i a population (all the members of the
same species in a given area)
2. Populations over populate (Malthus)
Organisms in nature produce more offspring than can
survive which leads to competition for limited
resources among members of a species
3.
Nature selection
The organisms with the desirable variations are
better adapted and out-compete those who are not.
4.
Descent with Modification.
Individuals with the best adaptations survive and pass
on the trait to the next generation.
Survival of the fittest & Natural Selection
Those members of the population w/ the best
natural variations (adaptations), will survive &
pass these traits onto their offspring. Those
without the variations will not survive
“Fitness is measured in the # of
grandchildren one has”
Nature selects which variations
are the best suited to the
environment.
Peppered Moth
Simulation
Natural Selection
In a population, there are variations
There is natural selection. Some
are selected out, some aren’t
There is heredity. Survivors reproduce
Descent with Modification
and are therefore fitter.
A new species/variety of only tan beetles
Natural Selection Lab
Gene pool
All the genes from a single population
combined together
50:50 with our lab
Gene frequency
Number of times a particular allele occurs in
the gene pool.
0.5: 0.5 at start of lab
We will watch the gene frequency change
through generations of the:
Small Lima bean
Large Lima bean
Natural Selection Lab
Generation
1
2
3
4
5
6
Total number of Beans in Bag
100
100
100
100
100
100
Total number of Small Lima beans
50
Total number of Large Lima beans
50
Number of Small Lima beans removed
Number of Small Lima beans remaining
Number of Large Lima beans removed
Number of Large Lima beans remaining
Total number of beans remaining in bag
Frequency of Small Lima beans remaining in bag
Frequency of Large Lima beans remaining in bag
1.0
Key:
___ = Small Lima
___ = Large Lima
.5
0
1
2
3
4
5
6
If you continued this lab through other
generations, what do you think would have
happened to the gene frequencies?
• Small Lima bean’s gene frequency
would continue to go up while the large
bean’s would decrease over time.
• Eventually, there wouldn’t be many
large beans so the small limas would
be easier to pick off (that’s all there is
now).
• The gene frequencies would then
change again.
• If all the larges though were picked out,
they would become extinct
Fossil Evidence
• Fossil evidence shows that
living things have been evolving
on earth for millions of years.
• Also showed that the
geographic distribution of
organisms lines up with the
movement of the earth’s crusts
& that newer (more modern)
forms of fossilized organisms
are found in the upper layers of
rock
Comparing Embryos
Which one of these is a
human, chicken, turtle, fish
or salamander?
•Early stages of
development of
many animals
with backbones
are very similar
•Children of
Evolution video
Look at the bones of the four animals below. What do you notice about all of
them?
Grasping, swinging
Walking
Swimming
Flying
Under each one, write down what the limb is used for in each animal
Based on what you see above, what conclusion could you draw about the
ancestry of the four animals?
Homologous Structures
Homologous structures
show common ancestry or
divergence from a common
ancestor.
• Same structures but
different functions
• Bones of our
forearm, the front
flipper of a dolphin,
the wing of a bat &
legs of a dog.
• Could all four limbed
animals with
backbones have
descended with
modification from a
common ancestors?
Analogous Structures have same function
but different structure
• Have similar environments
• Butterfly and Bird wing
• Yam and potato – both are tubers
• Why did we have an appendix?
• Why would a whale have hind leg bones?
• Why do we have wisdom teeth and why are they a
problem now?
• What’s with our coccyx?
• When eating a chicken wing, what’s with the thumb?
Thumb
What do these structures indicate about common ancestry?
What about structures that are no longer in use?
Vestigial organs
– Structures which no longer have a
function to the organism.
• Our appendix, hair, coccyx, wisdom teeth
These vestiges had a useful function at
one time but since they are no longer of
an adaptive use to the organisms, they
have become reduced with time.