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Evolution , Natural Selection,
and the History of Life
The Stories of Charles Darwin and
Alfred Russell Wallace

What is your “working definition” of
Evolution?

I don’t need the book answer, I would
like “your” answer.
A Quick History of Life
The Earth formed 4.6 BILLION years ago
 Early Earth was very unstable and too hot
for life to exist.
 3.9 Billion years ago Earth cooled enough
for water vapor to condense to form rain
and seas.
 3.5 Billion years ago the first living
organisms appear.

I. Origin Of Life

Life began during the first billion years of
Earth’s history (which is 4.5 billion years old).
 The ocean received organic matter from the
land and the atmosphere, as well as from
meteorites and comets.
 Substances such as water, carbon dioxide,
methane, and hydrogen cyanide formed key
molecules such as sugars, amino acids, and
nucleotides - the building blocks of proteins
and nucleic acids.
How it may have started

Planetary processes such as ocean
chemistry (mixing of organic matter), a
turbulent atmosphere (lightning, clouds,
solar radiation) and volcanic activity
together led to the formation of life.
Early life
Life began as single-celled microorganisms,
most likely anaerobic bacteria since no
oxygen was present in the atmosphere 3.5
billion years ago. Their fossilized structure
suggests that they were photosynthetic.
 Between 1 & 2 bya, the single-celled
eukaryotic organisms with their complex
system of organelles and membranes
evolved into multi-cellular organisms.

Increasing in complexity

The evolution of the
plants and animals
most familiar to us
occurred only in the
last 550 million years.
Evidence of Early life: The Fossil Record
Microbial life of the simplest type was
discovered in fossils and dated to come from a
time period of 3.5 billion years ago.
 The oldest evidence of more complex
organisms (eukaryotic bacteria) has been
discovered in fossils sealed in rocks
approximately 2 billion years old.
 Multi-cellular organisms (the familiar fungi,
plants, and animals) have been found only in
younger fossils:

Life Form
Millions of Years Since First
Known Appearance
Microbial (prokaryotic cells)
Complex (eukaryotic cells)
First multi-cellular animals
3500
2000
670
Shell-bearing animals
Vertebrates (simple fishes)
Amphibians
Reptiles
540
Mammals
Nonhuman primates
Earliest apes
Human ancestors
Modern humans
490
350
310
200
60
25
4
0.15 (150,000 years)

Many intermediate forms have been
discovered between fish and
amphibians, between amphibians and
reptiles, between reptiles and mammals,
and along the primate lines of descent in
the fossil record, showing the evolution
between species.
The origin of life according to the
scientific method.

Spontaneous generation – The process by
which life was thought to be produced by
non-living matter.


Biogenesis – The idea that living organisms
come only from other living organisms.


Disproved by Francesco Redi
Proved by Louis Pasteur
Miller and Urey test the theory of life starting
in the oceans.
Evolution of Cells
Protocell – A large ordered structure that carries
out some activities associated with life such as
growth, division , or metabolism.
 The first cells used organic molecules for food
and were prokaryotic cells referred to as
heterotrophic prokaryotes
 Archeabacteria – prokaryotes that live in harsh
conditions. Glucose is made by chemosynthesis

The theory of Evolution
Charles Darwin is credited with the concept
of Evolution, but he was not the first person
to suggest that organisms change over time.
 Several scientists before Darwin alluded to
the concept of Evolution. They never
explained how it could happen.
 Darwin gets the credit for the theory of
evolution because he described or
explained how evolution could occur.

Lets do a little research on the
history behind evolutionary thought

http://evolution.berkeley.edu/evolibrary/s
earch/topicbrowse2.php?topic_id=48
Evolution Defined
Evolutions was first define as a change
in a species over time.
 This first general definition was too
vague and general. It allowed for much
debate.
 A current and less arguable definition of
Evolution is:
 Evolution is the change in gene
frequency in a population over time.

Jean Baptiste de Lamarck

1. In the early 1800’s, Lamarck, a French
biologist, developed a theory of evolution based
on his belief in two biological processes.


1 The use and disuse of organs. Lamarck believed
that organisms respond to changes in the environment
by developing new organs or modifying old ones
(acquired characteristics). Disuse results in the
disappearance of the organ.
Inheritance of acquired traits. Lamarck believed that
these acquired characteristics were then passed on to
offspring.
Example of Lamarck’s theory
 Lamarck
believed that at one time giraffes had
short necks and ate grass. Then either grass
became scarce or other animals out-competed
the giraffes for the grass so they started eating
leaves off trees. As lower leaves became
scarce, they stretched to reach higher leaves.
Their necks gradually got longer and they
passed the longer necks to their offspring.
Alfred Russell Wallace
Another Naturalist that was interested in
Biology and Geology.
 Younger than Darwin, but came up with
the idea of organisms changing over
time.
 Wallace new that Darwin had already
been working on an explanation of
evolution and sent him a draft of his
theory.

Wallace and Darwin





Darwin read the theory and was worried that
Wallace would publish before him, but
encouraged the young naturalist.
Darwin was very methodical, in fact, his
friends thought too methodical.
Everyone “knew” Darwin had a theory
regarding evolution but was not publishing it
After much pressure from friends he presented
his information, along with Wallace at a
meeting.
Shortly after the meeting he published On the
Origin of Species
Darwin

Was a pigeon breeder and noticed that
people could select and breed for
specific traits.


Artificial selection – A technique in which
breeders select for a particular trait.
Darwin applied the idea of artificial
selection to the natural environment and
termed it Natural Selection.
Natural Selection

A mechanism for change in populations
that occurs when organisms with
favorable variations for a particular
environment survive, reproduce, and
pass on these variations on to the next
generation.
Darwin

1. As a naturalist, Darwin traveled to
South America on the ship the H.M.S.
Beagle. While there he found evidence
that the Earth was very old by observing
an earthquake and discovering marine
fossils on mountaintops. He also found
evidence of evolution.
Darwin
 While
on the Galapagos Islands,
Darwin noticed that plants and
animals were like those on the
mainland, but not exactly alike. He
realized that the species came from
the mainland and changed into a
new species. He came up with his
theory of Evolution by Natural
Selection.

Darwin observed that:
Individuals in a population have traits that vary
 Many of these traits are heritable (passed from
parents to offspring)
 More offspring are produced than survive
 Competition is inevitable
 Species generally suit their environment


Darwin inferred that:
Individuals that are best suited to their
environment are more likely to survive and
reproduce
 Over time, more individuals in a population will
have the advantageous traits


In other words, the natural environment
“selects” for beneficial traits

Darwin’s theory had 5
main points:

1. Variation exists
among individuals of a
species.

For example, some
gorillas have longer
arms than others,
some ladybugs have
more spots than
others, etc.
Darwin

Evolution by Natural Selection
2. All organisms compete for the
same limited resources.
Such competition would lead to the
death of some individuals, while
others would survive.
3.Organisms produce more offspring
than can survive.
The available resources cannot
support all these individuals.
Darwin
 4.
Evolution by Natural Selection
The environment selects
organisms with beneficial traits.
 5. Organisms with traits best suited to
the environment will reproduce and
pass on these traits at a greater rate
than organisms less suited to the
environment. This “survival of the
fittest” is called Natural Selection.
Conditions Necessary for Natural
Selection
Over production of offspring
 Variation of traits
 Individuals with favorable variations
survive and pass on variations to the
next generation.
 Gradually offspring make-up a larger
proportion of the population
 See handout

Origin of Variation

From where do the “fittest” get their beneficial
traits? Variations must be genetic (in the sex
cells) to be passed on to offspring. There are
two fundamental sources of variation in a
species:
Mutation - a change in the chemical
structure of the gene, so it will be passed
on to the offspring.
Genetic recombination - mixing of the
genes between chromosomes during
meiosis.
Selection Pressure

Selection Pressure is the force exerted
by nature which directs an organisms
evolution and causes one trait to b better
than another.
IV. Processes of Evolution

5 main processes that upset the genetic
equilibrium of a population:

A. Natural Selection – Disrupts a normal
population by allowing fit individuals to
survive and reproduce at higher rates
than less fit individuals. There are three
types of natural selection:
Natural Selection
1. Directional Selection – Natural
selection that proceeds in a given
direction.
 Ex.) Necks of giraffes – evolution has
proceeded in the direction of longer
necks.

Natural Selection
2. Stabilizing Selection – Selection that
eliminates the extremes of a trait causing
a reduction in variation of a species.
 Ex.) Leg length of rabbits – long legs are
eliminated because the rabbits can’t
crawl into a hole to escape predators,
short legs are eliminated because they
cannot run fast enough to escape
predators.

Natural Selection
3. Disruptive Selection – Selects against
the average and favors the extremes of a
trait.
 Acorns – squirrels do not eat the
smallest, not enough food. Squirrels do
not eat the largest, to hard to carry.
Squirrels eat the average, after many
years the average become eliminated.

Migration
B. Migration – The movement of
organisms into or out of a population.
 A herd of caribou lives in Canada. A
second, genetically different herd
migrates to mix with the first herd. The
gene pools of the two herds mix,
genetically changing the original
population.

2 Types Of Migration
1. Immigration – The movement of new
individuals into a population.
 2. Emigration – The movement of
individuals out of a population.

Genetic Drift
C. Genetic Drift – The change in gene
frequency of a population due to chance.
 Ex.) In a population of 16 long-horned
beetles, 15 are black and 1 is red. If
random mating occurs, there is a chance
the red won’t mate, thus eliminating that
trait from the population.

Isolation
D. Isolation – Isolation occurs when a
geographic boundary separates a population
into groups that can no longer interact.
Boundaries can include rivers, mountains and
canyons. Isolation often results in the evolution
of a new species.
 Ex.) The camel originated in the U.S. It
spread to Asia and South America over land
bridges during the Ice Ages. Over time the
separated populations evolved and became
different species – the camel in Asia and the
llama in South America.

Mutation

E. Mutation – Harmful mutations are
eliminated from a population because
the organism usually doesn’t live to
reproduce. Beneficial mutations are
passed on to offspring, thus changing
the population.
Sexual selection

A form of natural selection in which
individuals with certain traits are more
likely than others to obtain mates.

Mate choice based on a trait
V. Patterns of Evolution

A. Divergent Evolution – The process by
which related organisms become less
alike.
Divergent Evolution
1. Speciation – Divergent evolution
results in a new species.
 Ex.) A group of brown bears becomes
isolated from another group. The
isolated group moves into northern
Canada and eventually develops heads
and necks suited for swimming and white
fur, thus diverged from their ancestors.

Adaptive Radiation

2. Adaptive
Radiation – Process
by which individuals
of a new species
adapt to a variety of
habitats.
 Ex.) Darwin’s
finches adapt to
eating different types
of food by changing
beak types.
4 Types of Speciation
1. Allopatric speciation - physical barrier
divides population
 2. Peripatric speciation - small
founding population enters isolated niche
 3. Parapatric speciation - new niche
found adjacent to original one
 4. Sympatric speciation - speciation
occurs without physical separation

Allopatric Speciation

A population splits into two geographically isolated
populations.
 The isolated populations then undergo genotypic
and/or phenotypic divergence.
 become subjected to dissimilar selective pressures
 independently undergo genetic drift.
 When the populations come back into contact, they
have evolved such that they are reproductively
isolated.
Examples:

Differnces between organisms on Komodo island.
 Darwin's Galápagos Finches.
Peripatric Speciation

New species are formed in isolated, small peripheral
populations that are prevented from exchanging genes with
the main population.
 Related to the concept of a founder effect, since small
populations often undergo bottlenecks.
 Genetic drift is often proposed to play a significant role in
peripatric speciation.
Examples:
The Australian bird Petroica multicolor
The London Underground mosquito
Parapatric Speciation

A form of speciation that occurs due to variations in the
mating habits of a population within a continuous
geographical area.



In this model, the parent species lives in a continuous habitat
In contrast with allopatric speciation and peripatric speciation
where subpopulations become geographically isolated.
Niches in this habitat can differ along an environmental
gradient, hampering gene flow, and thus creating a cline.
Example: the grass Anthoxanthum tolerant to high mineral
content in soil near abandoned mines.
Sympatric Speciation




Species diverge while inhabiting the same place.
Examples of sympatric speciation are found in insects
that become dependent on different host plants in the
same area.
Fig wasps, cichlid fish
The existence of sympatric speciation as a mechanism
of speciation is still hotly contested
Types of Speciation (graphical)
Two other types of speciation

Polyploidization - change in the number of
chromosomes via mutation or reproduction.


Example: various plants and some amphibians
Hybridization - two different species reproduce
and the resulting offspring is fertile, but does
not reproduce with members of the two
original species.

Example: various plants
Convergent Evolution
B. Convergent Evolution – The process by
which distantly related organisms develop
similar characteristics because they share the
same environment.
 Ex.) Whales were once land mammals that
adapted to an aquatic environment by
changing from legs to flippers for swimming.
They began to resemble fish, which are not
closely related.

Convergent Evolution

Can lead to Mimicry
– the evolution of
one organism so it
resembles another.
 Ex. The Viceroy
butterfly, a nontoxic
insect, mimics the
Monarch butterfly, a
toxic insect.
Review: Disruptions to genetic
Equilibrium








Genetic equilibrium - no change in frequency of an
allele
1. Natural Selection
2. Migration (Immigration, Emigration)
3. Isolation
4. Genetic Drift
5. Sexual selection
6. Genetic recombination
7. Mutation
Punctuated Equilibrium

Proposed by Stephen Jay Gould

Contradicts Darwin’s concept of gradualism.

Gould proposed that that most sexually reproducing
species will experience little evolutionary change for most
of their geological history.
 Gould termed this a state of stasis.
 When evolution occurs, it is localized in rare, rapid events
of branching speciation.
 He termed the rapid branching cladogenesis.

Cladogenesis is the process by which species split into two
distinct species, rather than one species gradually
transforming into another.
The Tree of Life

“Unity in diversity” arises from “descent
with modification”


For example, the forelimb of the bat, human,
horse and the whale flipper all share a common
skeletal architecture
Fossils provide additional evidence of
anatomical unity from descent with
modification
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Darwin proposed that natural selection could
cause an ancestral species to give rise to
two or more descendent species


For example, the finch species of the
Galápagos Islands
Evolutionary relationships are often
illustrated with tree-like diagrams that show
ancestors and their descendents
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 1-22
Insect-eaters
Gray warbler finch
Certhidea fusca
Bud-eater
Seed-eater
Warbler finches
COMMON
ANCESTOR
Green warbler finch
Certhidea olivacea
Sharp-beaked
ground finch
Geospiza difficilis
Vegetarian finch
Platyspiza crassirostris
Mangrove finch
Cactospiza heliobates
Insect-eaters
Tree finches
Woodpecker finch
Cactospiza pallida
Medium tree finch
Camarhynchus pauper
Large tree finch
Camarhynchus
psittacula
Seed-eaters
Ground finches
Cactus-flowereaters
Small tree finch
Camarhynchus
parvulus
Large cactus
ground finch
Geospiza conirostris
Cactus ground finch
Geospiza scandens
Small ground finch
Geospiza fuliginosa
Medium ground finch
Geospiza fortis
Large ground finch
Geospiza
magnirostris
Fig. 1-22a
Insect-eaters
Gray warbler finch
Certhidea fusca
Bud-eater
Seed-eater
Warbler finches
Green warbler finch
Certhidea olivacea
Sharp-beaked
ground finch
Geospiza difficilis
Vegetarian finch
Platyspiza crassirostris
Fig. 1-22b
Mangrove finch
Cactospiza heliobates
Insect-eaters
Tree finches
Woodpecker finch
Cactospiza pallida
Medium tree finch
Camarhynchus pauper
Large tree finch
Camarhynchus
psittacula
Small tree finch
Camarhynchus parvulus
Fig. 1-22c
Seed-eaters
Ground finches
Cactus-flowereaters
Large cactus
ground finch
Geospiza conirostris
Cactus ground finch
Geospiza scandens
Small ground finch
Geospiza fuliginosa
Medium ground finch
Geospiza fortis
Large ground finch
Geospiza
magnirostris
Fig. 1-UN1
Evidence For Evolution
Fossil record
Microbial life of the simplest type was
discovered in fossils and dated to come from a
time period of 3.5 billion years ago.
 2. The oldest evidence of more complex
organisms (eukaryotic bacteria) has been
discovered in fossils sealed in rocks
approximately 2 billion years old.
 3. Multi-cellular organisms (the familiar fungi,
plants, and animals) have been found only in
younger fossils:
 1.
The Fossil record

4. Many intermediate forms have been
discovered between fish and
amphibians, between amphibians and
reptiles, between reptiles and mammals,
and along the primate lines of descent in
the fossil record, showing the evolution
between species.
The Fossil Record
 5.
There is also consistent evidence of
systematic change through time -- of
descent with modification (evolutionary
changes between classes of animals).
That is, fish came first, then amphibians,
followed by reptiles and finally mammals.
 No two classes made their first
appearance in the fossil record at the
same time.
B. Anatomical Evidence
 1.
Body parts with the same basic
structure are called Homologous
Structures.
These are structures in which the size
and shape are different, but the number
and arrangement of bones are the same.
 Homologous structures found in different
organisms suggest that these organisms
share a common ancestor.

An example of homologous
structures is:
whale flipper - lion
leg 4. Examples of
homologous
structures can also
be grouped by
function.
Anatomical Structures (Continued)
 Vestigial
Structures, structures that have been
greatly reduced in size and no longer serve
an important function, also provide evidence
for evolution.

An example of this is the small hipbones in whales
and snakes suggesting the whale and snake
came from an ancestor with hips, and the splintlike bone in horses that indicated an ancestor with
a side toe.
Human Vestigial Structures:
Ear muscles help monkey’s move ears to sense
danger, but do nothing in humans.
Appendix - used by ancestors to digest cellulose
of plants.
Coccyx (tail bone) - No longer needed for original
function of balance and mobility.
plica semilunaris - remnant of the nictitating membrane
(the "third eyelid") which is present in other animals.
5. Wisdom teeth - third molars that human ancestors
used to help in grinding down plant tissue.
6. Goose bumps - its purpose in human
evolutionary ancestors was to raise the body's
hair, making the ancestor appear larger and
scaring off predators. Raising the hair is also used
to trap an extra layer of air, keeping an animal
warm.
Anatomical Structures (continued)
 Analogous
Structures, body
parts that are similar in
function but not in basic
structure, are not evidence of
evolution.

a. An example of this type of
structure are the wings of birds,
insects, bats dinosaurs.
A. Moth
Wing

B. Pterosaur
Wing
C. Bird
Wing
D. Bat
Wing
All of these organisms use their wings to fly,
but they are composed of different structures.
C. Embryological Evidence

1. Studying organisms at very early
stages of development, while they are still
embryos, suggests different vertebrate
species share common genetic
instructions for embryo development.
The final bit of evidence for
Evolution is:

Similarity in DNA
Video: Albatross Courtship Ritual
Video: Blue-footed Boobies Courtship Ritual
Video: Galápagos Islands Overview
Video: Galápagos Marine Iguana
Video: Galápagos Sea Lion
Video: Galápagos Tortoise
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings