The Theory of Evolution

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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

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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.
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How does evolution explain the origin and
development of species?
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The Beginning of the Story

• Evolution begins with variation.
• NO VARIATION NO EVOLUTION
• What causes variation?

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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.

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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.

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Mutations may

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

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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

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Whether a mutation is positive or negative
depends the location of the mutation in the
genome

• True
• False

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Whether a mutation is positive or negative
depends on the environment of the organism.

• True
• False

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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.

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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.

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What specific name do we have for inherited
mutations?

• Chromosomes
• Markers
• Genes
• Gametes

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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

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What is the name of the people the scientist is
investigating?

1. Koi San
2. Africans
3. Kenyans
4. Aborigines

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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.

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

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• 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?
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• 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.

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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?

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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.

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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

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Voyage of the HMS Beagle

• Stopped in Galapagos Islands 500 miles off coast
  of Ecuador

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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"
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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
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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
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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.
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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

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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

?
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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.
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Natural Selection

• Overproduction
• Competition
• Variations
• Survival of the fit

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1. Overproduction

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

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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.

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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.

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• 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.

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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.

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• 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.

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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.
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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

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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.
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These changes can result in the appearance of a
new species. Evolution by natural selection
occurs.