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Evolution by Means of Natural
Selection (Ch.10)
10.1 Early Ideas About Evolution
TEKS 2B, 3F, 7B
Early scientists proposed ideas about evolution.
• Evolution is the biological change process by which
descendants come to differ from their ancestors.
• A species is a group of organisms that can reproduce
and have fertile offspring. (Linnaeus)
10.1 Early Ideas About Evolution
TEKS 2B, 3F, 7B
Historical thought
• Greek- Aristotle (3rd c. BC)- Scala Naturae- “great chain
of being” or the “ladder of life”
– Connects all living things moving toward a goal
• Literal Biblical view- the world was created in 6 days
– Earth is 6000 years old
– all species were created as they are today
10.1 Early Ideas About Evolution
TEKS 2B, 3F, 7B
de Buffon
• Everything is related; share a common ancestor instead
of arising separately
• Goes against any Christian beliefs.
Influence of Geology
James Hutton- gradualism
Things that change the earth take A LONG
TIME
Charles Lyell- current earth-shaping
processes are the same as the past
stressed that scientists must explain past
events in terms of processes that they can
actually observe,
Wrote Principles of Geology, read by Darwin
William Smith
Each layer (stratum) of rock had unique fossil
records
The older the strata, the more dissimilar the
organisms are to present forms
George Cuvier
Documented extinction as a common
occurrence
Thomas Malthus
 Population size link to
poverty and disease
 If human population
continued to grow
unchecked (grows
expontentially), it will be
limited by space and food
supply (grows
arithmetically)
 Population outgrows
resources and
competition kicks in
 That applies to more than just
us!
 Turtles lay hundreds of eggs,
few survive
 Trees set out hundreds of
seeds, how many actually
mature?
 There is some selecting factor
that decides which organisms
are most fit for survival…
Lamarck’s Hypothesis
 Tendency Toward Perfection
they are continually changing and acquiring features
that help them live more successfully in their
environments
Use and Disuse
organisms could alter the size or shape of particular
organs by using their bodies in new ways
 Inheritance of acquired characteristics
if during its lifetime an animal somehow altered a body
structure, it would pass that change on to its offspring
Why/How did giraffes develop long
necks?
Lamarck’s Giraffes
Lamarck’s Hypothesis (1809)
Lamarck’s hypothesis of evolution
was the first to recognize that
organisms are well suited for their
environment – this is a key concept
for future work.
Charles Darwin
 more-complex forms developed from less-complex
forms
 Species on the Galapagos Islands were similar
to the mainland, but differ in each environment
 Variation naturally exists within a natural or
domesticated population and some of that
variation is inheritable
Galapagos Finches
Alfred Wallace
Co-discovery of natural selection
Published with Darwin
Lesser known because he was poor.
So…
Why is Lamarck wrong?
How did his hypothesis positively influence
evolutionary thought?
Paleontology
Def: the study of collecting and studying
fossils
William Smith
Each layer (stratum) of rock had unique fossil
records
The older the strata, the more dissimilar the
organisms are to present forms
Fossils provide a record of evolution.
Paleontology is the study of fossils or extinct
organisms.
Theories of geologic change set the
stage for Darwin’s theory.
• There were three theories of geologic change.
– Catastrophism Catastrophes cause extinction and promote new
species
– Gradualism slow changes helped to promote new species who are
better adapted to the environment
– Uniformitarianism the process that are shaping the earth today have
been going on forever
Darwin observed differences among island
species.
Variation is a difference in a physical trait.
Galápagos tortoises that live in areas with tall
plants have long necks and legs.
Galápagos finches that live in areas with hardshelled nuts have strong beaks.
Natural Variation in Species
Darwin Believed that natural
variation already existed in a
species and the environment
chose the best suited variation
Darwin did not show a mechanism
for how traits were inherited
Galapagos Tortoises
 Morphology
matched
function in the
environment.
An adaptations is a
feature that allow an
organism to better
survive in its
environment.
– Species are able to adapt to
their environment.
– Adaptations can lead to
genetic change in a population.
Definitions and Concepts:
Adaptation – any inherited characteristic
that increases an organism’s chance of
survival and ability to reproduce.
Ex. Monarch butterfly is poisonous to eat
they have special coloration to warn predators
also viceroy butterflies copy their coloration to
protect themselves
Fitness – the ability of an organism to
survive and reproduce.
SECTION 3
Theory of Biological Evolution by means
of Natural Selection
 Struggle for Existence
 Survival of the “fittest”, or Natural Selection
Fitness- ability to survive and reproduce
Adaptations- can be morphological, behavioral, or
physiological
An adaptation may be an advantage in one environment
and a disadvantage in another!
 Natural Selection
Only acts on heritable traits
Does not form NEW characteristics (only mutations can
do that!)
Is backward looking, not planned
acts on the individual, but the effect is on the
POPULATION
Artificial Selection
Man chooses which traits are more
appealing to him, then breeds the
organism to produce those traits
Theory of Biological Evolution by means
of Natural Selection
Species alive today are descended with
modification from ancestral species that
lived in the distant past.
This process by which diverse species
evolved from a common ancestor unites
ALL organisms on Earth into a single
tree of life.
The story of the Peppered Moth
How did the industrial revolution change a
species of moth?
Peppered Moth Animation
Peppered Moth Simulation
Discussion questions:
1. What differences were present in the moths?
What caused those differences? Where they
differences in morphology or physiology?
2. Before the industrial revolution, which color of
organism had the adaptation that was most fit for
the environment?
3. What type of selective pressures acted on the
moths?
Definitions and Concepts:
Selective Pressure – any phenomenon
which alters the fitness of organisms within
a given environment. It is the driving
force of natural selection, and it can be
divided into two types of pressure: biotic or
abiotic.
Ex: predation, food supply, temperature.
Example of selective pressure:
Some antelopes are swift and instinctively run
in a zig-zag pattern. Some lions are fast
and powerful.
 What is the source of variation in antelopes?
 What is the selective pressure?
 What is the adaptation that made it
successful in the environment?
Read the following information and
answer the questions on the next
slide.
The wide use of antibiotics has caused many bacteria
like Mycobacterium tuberculosis to evolve a
resistance to antibiotics. Some of the bacteria in this
population contained mutant genes that defended the
bacteria from the antibiotic drug. These few bacteria
did not die when they were exposed to the antibiotic.
These resistant bacteria reproduced more bacteria
like themselves that were resistant to the antibiotics.
This resistance is evidence of change or evolution of
a species.
Activity – Bacteria Resistance
Activity – Bacteria Resistance
1. What was the ultimate source of
variation in the species?
2. What was the selective pressure
described?
3. What was the adaptation of the
organism that made it successful in the
changed environment?
4. How did the Mycobacterium
tuberculosis change?
Activity – Galapagos Finches
Thirteen species of finches live on the Galápagos, the famous
island group visited by Charles Darwin in the 1830s. The
finches have a variety of bill shapes and sizes, all suited to their
varying diets and lifestyles. Some birds have beaks better
suited for eating cactus; some have long beaks better suited for
eating insects, or short beaks for eating hard seeds.
A variety of finches ended up on moist, rainy islands in which there
was a shortage of seeds, but many grub-like insects were living
under tree bark. The long-beaked birds could survive on grubs,
and would pass their genetic traits to their offspring. The others
would die out. Natural selection caused the long beaked
‘woodpecker finch’ to survive.
Darwin did not believe that the environment was producing the
variation within the finch populations. He correctly thought that
the variation already existed and that nature just selected for
the most suitable beak shape and against less useful ones.
Activity – Galapagos Finches
1. What was the ultimate source of variation
in the species?
2. What was the selective pressure
described?
3. What was the adaptation of the organism
that made it successful in the changed
environment?
4. How did the finch change?
Deer Mice
 Deer mice are widespread across North America, but they
usually have dark coat, so that they can blend into dark soils
and stay hidden from owls. However, soil in Nebraska is lightcolored sand. Over a period of several thousand years the deer
mouse in Nebraska evolved a pale coat that helped it to evade
predators. Scientists at Harvard and at the University Of
California at Berkeley discovered a single gene called Agouti in
light colored mice which is expressed in higher amounts and for
longer than the genes that code for dark hair. The gene
emerged about 4,000 years ago, which was only a few
thousand years after the dark coated mice colonized the new
sandy home. Its spread was rapid. Agouti did not occur before
the colonization of the sandy environment, and when it did
appear selection acted on it to confer an advantage, making it
more widespread
Activity – Deer Mice
1. What was the ultimate source of variation
in the deer mice?
2. What was the selective pressure
described?
3. What was the adaptation of the organism
that made it successful in the changed
environment?
4. How did the population of deer mice
change?
1. The term “survival of the fittest” is
closely associated with Charles
Darwin’s ideas of change over time. If
an organism is “fit”, it most likely will –
A. become extinct
B. pass down its genes to an
offspring
C. migrate to a new ecosystem
D. change in order to survive
2. Lizards closely resemble the plants and
trees in which they live. This is most likely
because
A. the lizard has learned to change colors.
B. the lizard is smaller than the leaves of the
trees.
C. ancestors of the lizards with the same
traits survived and reproduced.
D. the food eaten by lizards lives in plants.
To break it down…
 Organisms produce offspring and those that do
not survive do not reproduce therefore they do
not pass down their genes
 Each organism has different advantages and
disadvantages in the struggle for existence.
 Individuals best suited the their environment
survive and reproduce most successfully
Section 4
Evidence of Evolution
Evidence of
Evolution
includes
The fossil record
Geographic
distribution of
living species
Homologous
body structures
Similarities
in early
development
which is composed of
which indicates
which implies
which implies
Physical
remains of
organisms
Common
ancestral
species
Similar genes
Similar genes
Figure 15–14 Geographic Distribution of
Living Species
Can indicate common
ancestry from fossil
forms that occupied a
continuous area.
Figure 15–14 Geographic Distribution of
Living Species
Can indicate similar
structures forming
due to similar
habitats (and
therefore similar
selective pressures)
Beaver
NORTH
AMERICA
Muskrat
Muskrat
Beaver and
Muskrat
Coypu
Capybara
Capybara
SOUTH
AMERICA
Coypu and
Capybara
Discuss with your neighbor…
What conclusion can you draw from the
information below?
Rhea – Native to South America
Ostrich – Native to Africa
Emu – Native to Australia
Evidence for evolution in Darwin’s time
came from several sources.
Fossils provide evidence of evolution.
•
Fossils in older layers are more primitive than those in upper layers.
Fossil record
 Relative age– deeper
things are older
 radioactive dating
gives an estimated
age in years.
 species that once
existed and are now
extinct.
Relative Dating
 uses the layers
of fossils
 older fossils are
found below
more recent
ones
 living organisms
resemble fossils
although
differences may
be evident
Radioactive Dating
 using carbon dating on rocks and fossils
to determine a more accurate time frame
in which the organism lived.
 We know how long it
takes for radioactive
carbon to decay. By
identifying how much is
left in a sample, we can
give it an age.
The Fossil Record shows
 transitional forms: fossils or organisms that
show the intermediate states between an
ancestral form and that of its descendants.
Have you noticed that organisms can be
different within the fossil record?
Gradualism – slight changes
within a population over time
(subtle)
Punctuated equilibrium – a
quick change in a population
(dramatic - indicates a major
event)
Stasis – the idea that during
periods of time, little if any
change is observed within a
population
EXAMINING FOSSIL ACTIVITY
Fossil formation
 For every organism that leaves a fossil, many
more die without leaving a trace.
Fossil formation
 When a fossil is discovered, rarely is it of a
complete organism.
 More often paleontologists must reconstruct an
extinct species from a few fossil pieces—
remains of bone, a shell, or leaves.
 When paleontologists study a fossil, they look for
anatomical (structural) similarities—and
differences—between the fossil and living
organisms.
Below is a drawing of the fossils found in a partial
excavation completed by a paleontologist.
Layer A
Layer B
Layer C
Layer D
Layer E
Which layer is the oldest? Which
layer is the youngest?
Oldest = F, Youngest = A
Do the layers support the idea that
change has occurred over a
long period of time?
Yes, water to desert conditions
What might have happened from
layer C to layer B?
erosion
Layer F
Common Ancestry
Common embryology, homologous
structures, and DNA comparisons indicate
that all living things are related in differing
degrees.
Linking organisms together and classifying
them based on relatedness is a hot topic
among biologists today.
Embryology
Similarity in early embryonic stages shows
relatedness.
While this early
comparison was
later found to be
doctored, it holds
a little truth
Ernst Haeckel
Embryology
 Related organisms share a common early embryology
 The more closely related, the more related their
embryological stages are.
 When we explore invertebrates and vertebrates, we will
explore comparative embryology in detail
Homologous structures
Turtle
Alligator
Bird
Mammal
Ancient lobe-finned fish
 Structures that arise from the same area of the
embryo, but give rise to different mature forms
Homology in mammalian appendages
– Analogous structures have a similar
function.
Human hand
Mole foot
Analogous structures are
not evidence of a
common ancestor.
Fly wing
Bat wing
Analogous Structures
 Archeopteryx- “finger
wing” extended single
digit
 Bird wing- “arm wing”
all “arm” is part of
wing
 Bat wing- “hand wing”
the wing is made up
of several elongated
digits
Let’s practice: Analogous &
Homologous structures
Vestigial Structures
Structures that have
become reduced in
size because they do
not have a true
contributing function or
role in survival
Dewclaws (E) in most
mammals serve no purpose
and have been reduced in
size
Vestigial Organs
Pelvic girdle in
whales and snakes
Appendix in
humans
Eye spots in cavedwelling animals
Structural patterns are clues to the
history of a species.
•
•
Vestigial structures are remnants of organs or structures that had a function in
an early ancestor.
Ostrich wings are examples of vestigial structures.
Homologous, Analogous or
Vestigial?
Dolphins (which are mammals)
and fish both have similar
body shapes adapted for
moving in water.
Analogous
Homologous, Analogous or
Vestigial?
This species of
cave-dwelling
salamander
has eyebuds,
but is
completely
blind.
Vestigial
Homologous, Analogous or
Vestigial?
Homologous
Human – 7 neck bones
Giraffe – 7 neck bones
Whale – 7 neck bones
Homologous, Analogous or
Vestigial?
The ear muscles, appendix,
and tailbone in humans. Vestigial
Homologous, Analogous or
Vestigial?
Indicates that two organisms
probably have a common
ancestor.
Homologous
Homologous,
Analogous or
Vestigial?
Compare the
entire
wing.
What about
the yellow
bones?
Within A – Homologous
a
a
Between A & B - Analogous
b
Section 5
Molecular and genetic evidence support
fossil and anatomical evidence.
Two closely-related organisms will have
similar DNA sequences.
Pseudogenes are sequences providing
evidence of evolution.
– no longer function
– carried along with functional DNA
– can be clues to a common ancestor
Below is a short section of DNA:
A C A T A T T A G
What do the A, C, T and G represent?
Now compare the DNA to a close
ancestor:
ALiving organism:
C A T A T T A G
A T A T A T T A C
Ancestor:
•On which nucleotide(s) do the sequences
differ?
•What is this difference called?
You try it!
“It’s molecular time” Directions
1. You have 9 nitrogen base
sequences from a section of DNA
similar to what you might find in a
human. Look for the sequence
labeled “living DNA”.
2. Find the closest ancestor to the
living DNA and place it below the
living DNA
3. Place the rest of the sequences in
the correct order, from present
(living) to oldest ancestor.
It’s Molecular Time Discuss:
What did you use to make your decision?
Were you correct in your order?
What did you use to make your decision?
Were you correct in your order
It’s molecular time
Assume that the rate of mutation is one
mutation for every 10,000 years. How
many years separate the “living DNA”
from its oldest ancestor?
We can also
compare amino
acid sequences
by looking at how
many differences
are there