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Darwin

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Darwin s Theory of Evolution Evolution, is change over time, OR is the process by which modern organisms have descended from ancient organisms. – PowerPoint PPT presentation

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Title: Darwin


1
Darwins Theory of Evolution
  • Evolution, is change over time, OR is the
    process by which modern organisms have descended
    from ancient organisms.
  • A scientific theory is a well-supported testable
    explanation of phenomena that have occurred in
    the natural world.

2
Evolution is a Theory Just like Gravity!
  • Evolution is a well supported explanation of
    phenomena that have occurred in the natural world
  • A theory in science is a well tested hypothesis,
    not just a guess

3
Evolution is when organisms change over time.
So, modern organisms descended from ancient ones
4
Charles Darwin born in England in 1809 Sailed
around the world 1831-1836
5
Voyage of the Beagle
How do you think Darwin came up with his theory?
6
Darwins Journey
7
  • Based on the excerpts you read from Darwins
    journal, The Voyage of the Beagle, what factors
    may have contributed to Darwins theory of
    evolution?

8
What did Darwins Travels reveal
  • The diversity of living species was far greater
    than anyone had previously known!!
  • Diversity Many different kinds of species
  • These observations led him to develop the theory
    of evolution!!

9
1. Patterns of Diversity
  • Darwin visited Argentina and Australia which had
    similar grassland ecosystems.
  • those grasslands were inhabited by very different
    animals.
  • neither Argentina nor Australia was home to the
    sorts of animals that lived in European
    grasslands.

10
Examples of Diversity
  • He saw rabbits in England but not in Australia
    even though the environment was similar

11
2. Living Organisms and Fossils
  • Darwin collected the preserved remains of ancient
    organisms, called fossils.
  • Some of those fossils resembled organisms that
    were still alive today.

12
Living Organisms and Fossils
  •  
  • Others looked completely unlike any creature he
    had ever seen.
  • As Darwin studied fossils, new questions arose.
  • Why had so many of these species disappeared?
  • How were they related to living species?

13
Fossils
Types of fossils Cast
mold Trace fossils
Imprints Frozen or amber Petrified fossils
14
Imprint
15
The Galapagos Island
  • A group of islands of the northwest coast of
    South America
  • The islands are close together but have very
    different climates
  • Darwin observed that the characteristics of many
    plants and animals varied among the different
    islands.

16
  • Examples from the Islands

Land tortoises
Galapagos finches
17
More examples on the Galapagos Islands
Blue footed booby
Marine Iguanas
18
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20
4. The Journey Home
  • Darwin Observed that
  • Many islands close together had different
    climates.
  • Characteristics of many plants and animals varied
    greatly among the islands

21
Darwin finally published his ideas in 1859 in
his book The Origin of Species that summarized
all his findings from his trip around the world.
22
LamarckTheory of acquired characteristics
  • Lamarck said organisms acquired traits by using
    their bodies in new ways
  • These new characteristics were passed to
    offspring
  • Lamarck was totally wrong!

23
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24
Evidence of Evolution
  1. Fossil Record
  2. Geographic Distribution of Living Species
  3. Homologous Body structures
  4. Similarities in Embryology

25
1. The Fossil Record
  • Fossil Record provides evidence that living
    things have evolved
  • Fossils show the history of life on earth and how
    different groups of organisms have changed over
    time

26
Relative vs. Absolute Dating
27
Relative Dating
  • Can determine a fossils relative age
  • Performed by estimating fossil age compared with
    that of other fossils
  • Drawbacks provides no information about age in
    years

28
  • 2. Geographic Distribution of Living Species
  • Similar animals in different locations were the
    product of different lines of descent

29
Homologous body structures
  • Structures that have different mature forms but
    develop from the same embryonic tissues.
  • Wings and legs all descended from fish fins.
  • e.g. Wing of bat, human arm, leg of turtle

Turtle
Alligator
Bird
30
Homologous Body Structures
31
Vestigial Organs
  • traces of homologous organs in other species
  • Organ that serves no useful function
  • e.g. Appendix in man

32
Similarities in Embryology
  • In their early stages of development, many
    animals look similar, providing evidence that
    they shared a common ancestry.

33
Embryological development
34
Artificial Selection
  • Nature provides variation, humans select
    variations that are useful.
  • Example - a farmer breeds only his best livestock.

35
1. Evolution by Natural Selection
  • What do you think natural selection mean?
    (Nature chooses, chooses what? Best adaptations
    for survival)
  • The Struggle for Existence-members of each
    species have to compete for food, shelter, other
    life necessities in order to survive.
  • Survival of the Fittest-Some individuals are
    better suited for the environment. Organisms with
    most favorable adaptation will survive.

36

Natural Selection
  • Natural selection is the process by which
    individual organisms with favorable traits are
    more likely to survive and reproduce.
  • Fitness is the ability of an individual to
    survive and reproduce in its specific
    environment.
  • Adaptation an inherited characteristic that
    increases an organisms chance of survival.

37
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2. Components of Natural Selection
  • Not all individuals will be able to reproduce.
  • Due to environmental issues, illness, etc
  • DIFFERENTIAL REPRODUCTION

Birds eat green beetles, not brown ones.
Whats Left?
Whats the end result?
39
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40
Components of Natural Selection
  • The brown beetles that are left will mate and
    have brown offspring.

The brown trait has a genetic basis.
This is called HEREDITY.
41
  • Finally, the brown trait (which is more
    advantageous) allows the beetle to survive in
    order to reproduce.
  • Eventually, all beetles in this population will
    be brown.
  • This PHENOTYPE has been SELECTED over the green
    phenotype.

Image courtesy of http//evolution.berkeley.edu/ev
olibrary/article/_0_0
42
3. Descent with Modification
  • Descent with Modification- Natural selection
    produces organisms that have different
    structures, establish different niches or occupy
    different habitats.
  • This causes todays species to look different
    from their ancestors.
  • Common Descent- were derived from common ancestors

43
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44
Summary of Darwins Theory
  • Organisms differ variation is inherited.
  • 2. Organisms produce more offspring than survive.
  • 3. Organisms compete for resources.
  • 4. Organisms with advantages survive to pass
    those advantages to their children.
  • 5. Species alive today are descended with
    modifications from common ancestors.

45
Evolution of Populations
  • Occurs when there is a change in relative
    frequency of alleles

46
VOCABULARY REVIEW
  • Evolution
  • change over time
  • NATURAL SELECTION
  • Individuals better adapted to the
    environment are able to survive and reproductive.
  • SURVIVAL OF THE FITTEST

47
NEW VOCABULARY
  • POPULATION
  • Group of individuals of same species that
    interbreed.
  • GENE POOL
  • Common group of all genes present in a
    population.

48
Variation and Gene Pool
  • Combined genetic information of all members.
  • Allele frequency is number of times alleles occur
    in the population.
  • Evolution Any change in the relative frequency
    of alleles in a population

49
Single-Gene vs. Polygenic Traits
  • Single-Gene trait any trait controlled by one
    gene (example tongue rolling)
  • Natural selection on single-gene traits can lead
    to change in allele frequencies and thus
    evolution. Distinct phenotype
  • Polygenic traits any trait controlled by two or
    more genes (example height in human) Many
    Phenotypes

50
  • Natural selection can affect the distribution of
    phenotypes in any of three ways
  • Directional selection- Individuals at one end of
    the curve have higher fitness than those in the
    middle. (Example seed size and birds beak size)
  • Stabilizing selection-Individuals near the center
    of the curve have higher fitness than those at
    either ends of the curve. (Example weight of
    human infants at birth).
  • Disruptive selection-Individuals at the upper and
    lower ends of the curve have higher fitness than
    those near the middle. (Eample seed size and
    bird beak size).

51
Natural Selection on Polygenic Traits
  • Shifts to
  • middle range
  • Shifts to
  • 2 extremes
  • Shifts to
  • 1 extreme

52
Genetic Variation
Gene Flow Movement of genes from one population
to another.
Mutation Changes in DNA
Sex Sexual reproduction causes new combinations
of genes.
53
Sources of genetic Variation in Populations
  • processes can
  • lead to this
  • Mutations -
  • change in DNA
  • sequence
  • Gene Shuffling
  • from sexual
  • reproduction

54
Genetic Drift
  • Suppose that some organism left behind a few more
    offspring than other organisms.
  • The ones that are left are the lucky ones. But
    their genes may be no more advantageous than
    anyone elses.
  • Entirely random.
  • Doesnt produce adaptations, only a mixing of the
    gene pool.

55
Genetic Drift changes populations.
  • Random change in allele frequency causes an
    allele to become common

56
  • Founder Effect genetic drift due to the
    migration of a small subgroup of a population.
    (example fruit flies migrating from mainland to
    different Hawaiian islands.)

57
Hawaiian Honeycreepers
An example of adaptive radiation these
species all diverged from a common ancestor
(founder species)
FOUNDER SPECIES
58
Conditions needed for Genetic Equilibrium
1
2
3
4
5
5
59
SPECIATION
  • Speciation is the formation of new species
  • As new species evolve, population become
    reproductively isolated.
  • 1. Reproductive Isolation Members of two
    population cannot interbreed produce fertile
    offspring.

60
ISOLATING MECHANISMS..
  • 2. Behavioral Isolation - capable of breeding
    but have differences in courtship rituals (EX.
    Meadowlarks)
  • 3. Geographical Isolation Separated by
    geographic barrier like rivers ,mountains, or
    bodies of water (ex squirrel)
  • 4. Temporal Isolation Two or more species
    reproduce at different times.

61
Table 23.1a
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