HISTORY

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Selective use or disuse of organs caused organisms to acquire certain traits—called acquired characteristics
Organisms then passed these traits on to their offspring
Problems?

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1831
Voyage around the world
Darwin heavily influenced by Galapagos Islands

People also believed that the Earth had not changed during those few thousand years .
People also believed in fixity of species; in other words, species never changed .
After careful observation and study of new scientific discoveries,
Darwin began to think otherwise.
The first dinosaur to be described scientifically was Megalosaurus by William Buckland in 1824.

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Observations:
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Diversity of life
Animals uniquely adapted to habitats
Diversity of animals from similar habitats in geographically diverse places
Similarity between some organisms and fossils

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Each island has a diverse climate
Organisms showed diversity between islands
Organisms adapted to conditions on their island

Many of Darwin’s conclusions were based on observations of wildlife in the Galapagos
Islands.
The Galapagos Islands lie 500 miles west of Ecuador in the
Pacific Ocean, directly on the equator.
“Galapagos” means turtle.

In particular, Darwin observed something odd about the finches: they all looked like a bird he had seen on the South
American continent.

Darwin wondered if the birds and other animals had been created to match their environment, why didn’t these birds look like the birds of the
African continent, since the environments of both the Galapagos and
Africa were similar.

Darwin guessed that some of the birds from South America migrated to the Galapagos.
Once on the islands, the birds must have changed over the years.

cactus finch large ground finch woodpecker finch
This would explain the numerous species of birds present.

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Published in 1859 (nearly 30 years after the Beagle voyage)
Became a prominent work of scientific literature

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Natural Selection
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Struggle for existence
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Natural variation occurs in all populations due to mutations
Natural selection occurs because the fittest in each environment survive, reproduce and pass on their genes
Survival of the fittest

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Use natural selection to explain why giraffes have long necks.

Darwin concluded:
Each species has descended, with changes, from other species over time.
Darwin called this…
Descent With Modifications or
(change in species over time)

Darwin extended these principles to biology, which helped him form his theory of…

Five basic components of

1. All species have genetic variation.
Every species is different, even within itself.
Look around you…are you all the same?

2. Organisms produce more offspring than can survive. Many that survive do not produce offspring.
The female green sea turtle lays a clutch of about
110 eggs. She may lay several clutches.
It is likely that less than 1% of the hatchlings will ever reach sexual maturity.

3. Since more organisms are produced than can survive, there is competition (struggle for existence).
Competition exists WITHIN and AMONG species.
Within and Among Species for food water shelter space
And Within a Species for mates

The constant struggle for survival is affected by short-term natural disasters. (drought, fires, floods, snowstorms, hurricanes, and tornadoes)
The constant struggle for survival is also affected by long-term changes in the environment. (ice ages, biome shifts, etc)

4. Survival of the fittest Some organisms are more suited to their environment as a result of variations in the species.
Fitness: the ability of an individual to survive and reproduce in its specific environment. Fitness is a result of adaptations.
Individuals that are fit to their environment survive and leave more offspring than those who aren’t.
He who spreads the most genes wins!
1st

5. Decent with modification: Living species today are descended with modifications from common ancestral species that lived in the past.
Characteristics of fit individuals increase in a population over time.
Over time, genes for less favored characteristics will be eliminated from the gene pool.
Example: giraffes and their increasingly longer necks.

Natural Selection: Survival of the Fittest
An adaptation is any inherited characteristic (a genetic variation) that can increase an organism’s chance of survival.
because of need or desire to the environment changes.
survive. The organism either

As the environment changes, organisms must have variations that allow them to survive
(adapt) to those changes or die
If an entire population of a species cannot adapt, that species becomes extinct.

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Directional Selection —organisms with traits at one end of the curve are fittest. The curve will move in that direction in future generations.
Low mortality, high fitness
High mortality, low fitness

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Stabilizing Selection —
Individuals in the middle of the curve are most fit.
Stabilizing Selection
Low mortality, high fitness
High mortality, low fitness

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Disruptive Selection —Individuals at each end of curve are most fit.
Can lead to speciation.
Low mortality, high fitness
High mortality, low fitness
Beak Size
Disruptive Selection
Largest and smallest seeds become more common .
Population splits into two subgroups specializing in different seeds.

evolution are grouped into five main categories:
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Biochemical
Fossil Record
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Comparative
Anatomy
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Biogeography
Observable Events

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Paleontology
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Fossil – remains or traces of an organism that lived long ago
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Remains: ex. bone, tooth, or shell
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Traces: ex. burrow, footprint, or imprint

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Most fossils are found in layered sedimentary rock
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Oldest fossils are on the lowest layer

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Comparing fossils from different layers shows:
 Life on Earth has changed
 Increased number of life forms

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THE GENETIC CODE
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Triplets of DNA nitrogen-base sequences that code for specific amino acids
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The amino acid triplet is the same in almost all organisms.

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The similarity of triplet DNA codes making-up amino acids shows:
 A probable common ancestor for all life on
Earth

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“Universal” GENETIC CODE
 Similar genes
 Over the ages, the genetic code has passed unchanged
(or nearly so) from parent to offspring.

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AMINO ACID SEQUENCING
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The amino acid sequence in a particular protein is compared between organisms.
27
67 1
45
Number of differences from human hemoglobin

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Comparing amino acid sequence shows:
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Closeness of relationship
A probable common ancestor among has 146 amino acids
Amino Acid Difference in
Hemoglobin Compared with Human
Species Difference
Gorilla 1
Rhesus Monkey 8
Mouse
Chicken
Frog
Lamprey
27
45
67
125

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CLADOGRAM: diagram that shows the evolutionary relationship among a group of organisms.
A
B
Species Difference
Gorilla
Monkey
Mouse
Chicken
Frog
Lamprey
1
8
27
45
67
125
C
D Where would the common ancestor be?
E
F
G
Common ancestor
150
50
40
30
20
10
100
Number of Amino Acid Differences
0

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HOMOLOGOUS STRUCTURES
 structures with similar structure but different function
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(ex: turtle, alligator, bird, mammal)
Turtle
Alligator
Bird
Mammal

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Homologous structures show
 Similar genes
 Descent from a common ancestor
Turtle
Alligator
Ancient lobe-finned fish
Bird
Mammal

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VESTIGIAL STRUCTURES
 organs so reduced in size that they are nonfunctioning remnants of similar organs in other species
 ex: human tailbone, appendix, whale pelvis

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Vestigial structures show:
 an organism’s evolutionary past
 a common ancestor with species that have similar structures that are still functioning

COMPARATIVE ANATOMY
Analogous Structures
 Unrelated species have evolved to have similar adaptations

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EMBRYOLOGY
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Embryos of different species may appear similar in early stages of development
 ex: vertebrate development

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Comparison of similarities in embryos can show:
 Relationship to a common ancestor

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GEOGRAPHIC DISTRIBUTION
OF ORGANISMS
Beaver
 organisms living widely apart
(even different continents) may
Muskrat
Beaver and
Muskrat
Coypu
Capybara
Coypu and
Capybara be similar because they share a common ancestor
 Shows common ancestor

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Some changes in species have been observed and studied:
Peter & Rosemary
Grant’s Study of
Beak Size Shift in
Darwin’s Finches
H. Kettlewell’s Study of Peppered Moth
Color Shifts

 Observable events show that evolution is an ongoing process
Peter & Rosemary
Grant’s Study of
Beak Size Shift in
Darwin’s Finches
H. Kettlewell’s Study of Peppered Moth
Color Shifts

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Convergent Evolution
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Distantly related organism evolve similar traits; give rise to analogous structures
Examples:
Bird and butterfly wings
Streamlined shapes of fish, whales and seals

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Divergent Evolution
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Species that once were similar become more and more distinct

Adaptive Radiation is a form of divergent evolution.
This happens as competition leads organisms to fill different ecological niches to enhance survival.
Darwin’s Finches

(and here)
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Coevolution happens when 2 organisms develop together.
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Example: Flowering plants and the organisms that pollinate them.

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Divergent Convergent Parallel
(and here)

• Is about the formation of new species

• This can cause different traits to arise in each population. This is called divergence
• When the divergence is great enough that the two populations will no longer interbreed, the two populations have become different species.

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Speciation can occur when organisms become isolated and disruptive selection occurs. There are several different types of isolation that could lead to speciation
Low mortality, high fitness
Disruptive Selection
Largest and smallest seeds become more common .
Beak Size

• Reproductive Isolation/Behavioral
- any aspect of structure or behavior that prevents interbreeding
• ex. the development of different mating calls

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Species are capable of interbreeding, but don’t because of different mating rituals
Example: Different songs by songbirds

• Geographic Isolation
-Populations can be separated by geographic barriers ex. mountains, rivers

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Species don’t interbreed because they don’t reproduce at the same time
Example: some flowers pollinate during the day, some pollinate at night

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No change in the traits of a population
Hardy-Weinberg principle
Only happens in large populations with random mating, low immigration of organisms, and low percentage of genetic mutations

Four causes of evolutionary change:
1. Mutation: fundamental origin of all genetic
(DNA) change.
Chromosomal mutation
Point mutation
66
…at one point on the DNA
…entire chromosomes affected

Four causes of evolutionary change:
1. Mutation: fundamental genetic shifts.
2. Genetic Drift: isolated populations accumulate different mutations over time.
67
In a continuous population, genetic novelty can spread locally.

Four causes of evolutionary change:
1. Mutation: fundamental genetic shifts.
2. Genetic Drift: isolated populations accumulate different mutations over time.
Local spreading of traits
68

Four causes of evolutionary change:
1. Mutation: fundamental genetic shifts.
2. Genetic Drift: isolated populations accumulate different mutations over time.
Local spreading of traits
69

Four causes of evolutionary change:
1. Mutation: fundamental genetic shifts.
2. Genetic Drift: isolated populations accumulate different mutations over time.
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Spreading process known as ‘gene flow’.

Four causes of evolutionary change:
But in discontinuous populations, gene flow is blocked.
71

Four causes of evolutionary change:
Of course, this works at many loci simultaneously
72

1.
Mutation: fundamental genetic shifts.
2. Genetic Drift: isolation
 accumulate mutations
3. Founder Effect: sampling bias during immigration. When a new population is formed, its genetic composition depends largely on the gene frequencies within the group of first settlers.
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Human example: your tribe had to live near the Bering land bridge…

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…to invade & settle the ‘New World’!

Galapagos Finches
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Audeskirk & Audeskirk, 1993

1. Mutation: fundamental genetic shifts.
2. Genetic Drift: isolation
 accumulation of mutations
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3. Founder Effect: immigrant sampling bias.
4. Natural Selection : differential reproduction of individuals in the same population based on genetic differences among them.

1. Mutation: fundamental genetic shifts.
2. Genetic Drift: isolation
 accumulation of mutations
3. Founder Effect: immigrant sampling bias.
4. Natural Selection : reproductive race
78
These 4 interact synergistically

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Darwin’s theory of evolution gave rise to the study of phylogeny —the study of evolutionary relationships among organisms. Those with more similar characteristics were considered to have a more recent common ancestor.

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Many biologists now only classify using cladistic analysis — using only evolutionary innovations.
Derived characters
(evolutionary innovations) are used to construct a cladogram.

Cladograms vs. Traditional
Classification
Appendages Conical Shells Crustaceans Gastropod
CLASSIFICATION
BASED ON VISIBLE
SIMILARITIES
Molted exoskeleton
Segmentation
Tiny free-swimming larva
CLADOGRAM

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Gradualism – species originate through a gradual build-up of new adaptations
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Punctuated Equilibrium – speciation occurs quickly in rapid bursts, with long periods of stability in between

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Species A gradually turning into Species
B
Think-Pair-Share:
How would a phylogenetic tree look if one species was gradually changing into another

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With a different gene pool or a burst of mutations, this isolated group rapidly evolves into a separate species.
Think-Pair-Share:
What might cause punctuated equilibrium?
What would a phylogenetic tree look like if punctuated equilibrium had occurred?