The Theory of Evolution by Natural Selection

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The Theory of Evolutionby Natural Selection

• Part 2 Natural Selection

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7 Points to Remember

1. Overproduction
2. Competition
3. Variation
4. Adaptation
5. Natural Selection
6. Inheritance
7. Speciation

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1. Reproduction

• Every species is capable of producing far more
  offspring than are needed to maintain a stable
  population.
• Yet, generally, populations of organisms are
  stable within an environment.
• What are some ways that species can reproduce?

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2. Competition

• Living space and food resources are limited, so
  offspring from each generation must compete in
  order to live.
• They compete with each other, and with other
  species for the resources.
• Only a fraction will survive long enough to
  reproduce.
• These environmental pressures are what helps keep
  population sizes stable.

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2. Competition - 2
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5. Competition - 3
Survival of the Fittest

• MEANING The idea that species adapt and change
  by natural selection with the best suited
  mutations becoming dominant
• ORIGIN This expression is often attributed to
  Charles Darwin and although it appears in the
  fifth edition of his Origin of Species (1869), it
  is there attributed to Herbert SpencerThe
  expression often used by Mr. Herbert Spencer of
  the survival of the fittest is more accurate..
• Spencer had published The Principles of Biology
  in1864. In that he referred to survival of the
  fittest twice
• "This survival of the fittest, implies
  multiplication of the fittest."
• "This survival of the fittest... is that which
  Mr. Darwin has called 'natural selection, or the
  preservation of favoured races in the struggle
  for life'.
• By 'fittest', of course, Spencer and Darwin did
  NOT have in mind the commonly used meaning of the
  word now, i.e. the most highly trained and
  physically energetic. The 'fittest' referred to
  here are those animals which are the most suited
  to their environment, i.e. those which are best
  fitted to survive.

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3. Variation

• Individuals of any species vary in their
  characteristics. These differences are variations
  within a species.
• What produces these variations?
• What form of reproduction mixes genetic material
  from two parents?

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3. Variation - 2
How do you account for the variation in a zebras
stripes? How do you account for the regularity in
a zebras stripes?
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3. Variation - 3
People around the globe have taken advantage of
those variations, and selectively bred organisms
of domestic plants and animals to accumulate the
characteristics they were looking for. There is a
big difference between selective breeding and
natural selection (can you explain the
difference?), but the result is the same
gradual change in characteristics over time.
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4. Adaptations

• An adaptation is any characteristic that improves
  an organisms chance of survival and reproduction
  in its environment.
• What molecule codes for an organisms
  characteristics?
• How could that molecule vary from individual to
  individual?

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4. Adaptations - 2
What adaptations make these organisms well-suited
to their environments?
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4. Adaptations - 3

• What is the difference between
• adapting to ones environment and
• having an adaptation to that environment?

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5. Natural Selection

• The environment (nature) selects for organisms
  most suited for each environment by eliminating
  the unfit. Adaptations that are not suitable for
  an environment are weeded out.
• Organisms most suited survive reproduce.
• Selective Pressures
• Climate/Weather
• Resource availability
• Predation
• Sexual Selection

Source http//evolution.berkeley.edu
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5. Natural Selection - 2

• The fittest survive to pass on their DNA to the
  next generation. (Survival of the fittest)
• Offspring inherit these better characteristics
  and as a whole the population improves.

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5. Natural Selection - 3
IMPORTANT POINTS 1

• Individuals do NOT evolve.
• Populations--and therefore species--do.

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5. Natural Selection - 4
IMPORTANT POINTS 2

• Natural Selection does not move in a
  pre-determined direction!
• Organisms dont get what they need to
  survive.
• Organisms dont get to choose their DNA or
  characteristics that would help them survive.
• The changing earth determines what will and can
  survive.

Source http//sci.waikato.ac.nz
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5. Natural Selection - 5
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5. Natural Selection - 6

• The environment (nature) selects for organisms
  most suited for each environment by eliminating
  the unfit. Adaptations that are not suitable for
  an environment are weeded out.
• Organisms most suited survive reproduce.
• Selective Pressures
• Climate/Weather
• Resource availability
• Predation
• Sexual Selection

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6. Inheritance

• Those best adapted to their environment will
  survive to reproduce.
• They pass on their genetic information (DNA) to
  the next generation.

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6. Inheritance - 2

• The environment (nature) selects for organisms
  most suited for each environment by eliminating
  the unfit. Adaptations that are not suitable for
  an environment are weeded out.
• Organisms most suited survive reproduce.
• Selective Pressures
• Climate/Weather
• Resource availability
• Predation
• Sexual Selection

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6. Inheritance - 3

• Lamarck thought that a trait acquired during an
  organisms life could be passed on.
• Example Giraffes that stretched their necks to
  reach higher branches for food would pass the
  longer necks to their offspring.
• We now know this is wrong.

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6. Inheritance - 4
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6. Inheritance - 5

• Darwin did not know anything about DNA or genes
  or genetics or inherited characteristics.
• He inferred everything about it from his careful
  observations from nature.
• Darwin's theory of descent with modification was
  accepted by most scientists worldwide within ten
  years of its publication in 1859.
• However, his theory of natural selection was
  widely criticized, and by the turn of the 20th
  century was widely considered to be dead.
• However, the work of Gregor Mendel a
  Czechoslovakian monk, who discovered the
  foundations of what we now call genetics,
  provided a mechanism by which Darwin's theory
  could be revived and expanded.
• Gregor Mendel published his work with peas in
  1865 (Six years after Darwins Origin of Species)

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7. Speciation

• Over many generations, favorable adaptations
  gradually accumulate in a species and bad ones
  tend to disappear.
• Eventually, accumulated changes become so great,
  the result is a new species.
• Formation of a new species is called Speciation
• Speciation takes many, many, many generations to
  occur.

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7. Speciation - 2

• Speciation may occur due to
• Geographical isolation
• Reproductive isolation
• Genetic drift