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The Theory of Evolution

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Title: The Theory of Evolution


1
The Theory of Evolution
  • In science, theories are statements or models
    that have been tested and confirmed many times.
  • Theories have some important properties
  • They explain a wide variety of data and
    observations
  • They can be used to make predictions
  • They are not absolute
  • They serve as a model of understanding the world
    and can be changed as the world view changes

2
The Theory of Evolution is considered a Unifying
Theory of Biology, because it answers many of
these questions and offers an explanation for the
data.
3
How does evolution explain the origin and
development of species?
4
The Beginning of the Story
  • Evolution begins with variation.
  • NO VARIATION NO EVOLUTION
  • What causes variation?

5
What causes variation?
  1. List 5 types of variation.
  2. List 3 things that can cause variation in an
    organism?
  3. Write them on your clear board.
  4. Transfer them into your notes.

6
In the real world, how do mutations come about?
  • Internal
  • Replication errors
  • High energy molecules generated within the
    organism free radicals.
  • External
  • Chemicals, i.e. mutagens
  • Radiation, e.g. UV, cosmic rays
  • See video.

7
Mutations may
  1. Have positive effects
  2. Have negative effects
  3. Have no effect
  4. All of the above

8
All of the following can be causes of mutation
except
  1. Mutagenic chemicals
  2. An organisms need to be successful
  3. Radiation from the sun
  4. Free radicals

9
Whether a mutation is positive or negative
depends the location of the mutation in the
genome
  • True
  • False

10
Whether a mutation is positive or negative
depends on the environment of the organism.
  • True
  • False

11
Which of the following statements is false
  1. Mutations occur all the time.
  2. Everyone has mutations.
  3. Mutations always lead to a decrease in success of
    the organism.
  4. Mutations can be caused by a variety of factors.

12
Tracking Mutations
  • Mutations occurring in the genes of the gametes
    are inherited by offspring.
  • These mutations may show up through thousands of
    generations as the same chromosome is transmitted
    from parent to child.
  • Understanding these mutations can tell us a lot
    about the ancestry of organisms including humans.

13
What specific name do we have for inherited
mutations?
  • Chromosomes
  • Markers
  • Genes
  • Gametes

14
What genetic material does a man always inherit?
  1. His mothers paternal chromosomes
  2. His fathers paternal chromosomes
  3. His fathers Y chromosome
  4. All of his fathers chromosomes

15
What is the name of the people the scientist is
investigating?
  1. Koi San
  2. Africans
  3. Kenyans
  4. Aborigines

16
Why is Dr. Wells so interested in these bushmen?
  1. He thinks they may have some special genes that
    can be used in medicine.
  2. He thinks they may be the group most closely
    related to our ancestors who left Africa.
  3. He thinks they may have invented the bow and
    arrow.
  4. He thinks they may have invented spoken language.

17
  • Meiosis and fertilization allow for great
    diversity in sexual species compared to asexual
    species.

18
  • In evolutionary terms, sex is more important than
    life itself. Sex fuels evolutionary change by
    adding variation to the gene pool. The powerful
    urge to pass our genes on to the next generation
    has likely changed the face of human culture in
    ways we're only beginning to understand.

Why Sex?
19
  • Traits can be positive, negative or neutral in a
    given environment.
  • The alleles coding for negative traits are likely
    to be reduced in the presence of alleles for more
    favorable ones.

20
Team Question
  • The types of variation we have been discussing
    can have an impact on the success of an organism.
  • Biologically speaking, what is success?

21
Essential requirements for Evolution
  • Variation All life forms vary genetically within
    a population. It is this genetic variation upon
    which selection works.
  • Inheritance Genetic traits are inherited from
    parents and are passed on to offspring.
  • Selection Organisms with traits that are
    favorable to their survival get to live and pass
    on their genes to the next generation.
  • Time Evolution takes time. Evolution can happen
    in a few generations, but major change, such as
    speciation, often takes long periods of time.

22
CHARLES DARWIN 1809-1882
  • English
  • Traveled around the world on the Beagle famous
    in the Galapagos islands
  • Observed many species and fossils
  • Why did some species survive while others became
    extinct?
  • Natural selection

23
Voyage of the HMS Beagle
  • Stopped in Galapagos Islands 500 miles off coast
    of Ecuador

24
I have called this principle, by whicheach
slight variation, if useful, is preserved, by
the term Natural Selection.   Charles Darwin
from "The Origin of Species"
25
NATURAL SELECTION
Organisms with traits well suited to an
environment are more likely to survive and
produce more offspring than organisms without
these favorable traits
26
Types of selection
There are three types of selection disruptive,
stabilizing and directional.
Selection causes some traits to survive and
spread, while others are lost. A selection
pressure determines which traits are successful.
Selection can be represented using graphs showing
the distribution of individuals with a particular
trait.
Starting population has a normal distribution of
traits.
number of individuals
trait
mode
27
Types of selection
Selection can cause the mode and/or distribution
to change.
mode
mode
mode
number of individuals
number of individuals
number of individuals
trait
trait
trait
disruptive
directional
  • stabilizing

Selection pressure toward the extremes creates
two modal values.
Selection pressure toward the center increases
the number of individuals at the modal value.
Selection pressure toward one extreme moves the
mode in this direction.
28
Earlier ideas on Evolution
  • LaMarck
  • evolution by acquired traits
  • creatures developed traits during their lifetime
  • give those traits to their offspring
  • example
  • in reaching higher leaves giraffes stretch their
    necks give the acquired longer neck to
    offspring
  • not accepted as valid

29
Darwins view of Evolution
  • giraffes that already have long necks survive
    better
  • leave more offspring who inherit their long necks
  • variation
  • selection survival
  • reproduction inheritance of more fit traits

?
30
Could Darwin explain everything?
Darwin made extensive use ofspecimens and fossil
evidence toexplain his theory of evolution,but
because DNA andgenes had not yet
beendiscovered, he was unableto explain why
traits varied within individuals or how they were
inherited.
Victorian scientists found it difficult to test
Darwinstheory. For his theory to work, the
Earth needed to be millions of years old, but its
age was not known at that time.
In addition, little was known about the process
of fossilization or how to explain gaps in the
fossil record.
31
Natural Selection
  • Overproduction
  • Competition
  • Variations
  • Survival of the fit

32
1. Overproduction
  • Organisms produce more offspring than the
    environment can support.
  • There is not enough food or living space for all
    the offspring.

33
2. Competition
  • Overproduction leads to a struggle.
  • All the organisms compete for food, water, and
    the other necessities of life.
  • Only those organisms that are well suited to
    their surroundings survive and reproduce.
  • The rest die.

34
3. Variations
  • Organisms of the same species are very similar.
  • But they do have individual differences among
    traits, or variations.
  • These differences are important in the struggle
    for survival.

35
  • For example, extra speed can mean the difference
    between life and death. A fast wildebeest may
    escape an attacking lion. A slower neighbor may
    become the lions next meal.

36
4. Survival Of The Fit
  • Organisms with traits that make them well
    adapted, or suited to the environment, survive
    and reproduce.
  • Darwin used the term natural selection to
    describe the survival of organisms with favorable
    traits.

37
  • They, in turn, pass their favorable traits to
    their offspring.
  • The offspring are then more likely to survive.
  • As the process of natural selection goes on over
    many generations, species change.

38
Galápagos finches
In the Galápagos, Darwin noticed that different
islands had different types of finches, with
different types of beak.
  • Some finches had strong and claw-like beaks,
    suitable for crushing seeds.
  • Other finches had thin and delicate beaks,
    suitable for picking insects from holes in the
    ground.

Darwin thought all the finches could have evolved
from one type of finch that came from the
mainland.
39
Darwins finches
  • Darwins conclusions
  • variations in beaks
  • differences in beaks in the original flock
  • adaptations to foods available on islands
  • natural selection for most fit
  • over many generations, the finches were selected
    for specific beaks behaviors
  • offspring inherit successful traits
  • accumulation of winning traitsboth beaks
    behaviors
  • separate into different species

40
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41
Peppered moths
Peppered moths rest on tree trunks during the
day. Some are light colored and others are dark.
When cities were very polluted in the 19th
century the number of previously rare dark
colored moths increased, as they were better
camouflaged against predators on soot-stained
trees.
Cities are cleaner now. What difference has this
made?
The number of light colored moths is increasing.
42
These changes can result in the appearance of a
new species. Evolution by natural selection
occurs.
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