IB Topic 5.4: Evolution

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IB Topic 5.4 Evolution

• Individuals do not evolve, populations do

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What is evolution?

• Evolution
• Cumulative change in the heritable
  characteristics of a population
• Change over time
• Simpsons couch gag
• http//www.jibjab.com/view/131239

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Whats the evidence for evolution?

• Charles Darwin
• Contributed more to our understanding of
  evolution than anyone else
• Born 1809
• Traveled on the H.M.S. Beagle
• In 1831 set sail from England for a voyage around
  the world (see page 369 for a map of his travels)
  
• Made numerous observations and collected evidence
  that led him to propose a radical and
  revolutionary hypothesis about how life changes
  over time
• Evolution
• See Packet
• Fossil record
• Selective breeding (artificial breeding) of
  domesticated animals
• Homologous structures
• You are responsible for outlining/knowing these
  aspects

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Struggle for existence

• Organisms produce many more offspring than
  survive to be mature individuals
• Darwin did not coin the term struggle for
  existence but it does sum up the point that
  over-production of offspring in the wild leads to
  their competition for resources

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Some examples
Organism No. of eggs/seeds/young per brood or season
Rabbit 8-12
Great tit 10
Cod 2-20 million
Honey bee (queen) 120,000
Poppy 6,000
Many of these offspring die before they reproduce
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Darwins Observations

• 1. Observation
• Populations tend to reproduce rapidly and if
  every individual survived, there would be
  exponential growth
• Not the case
• Seems to be a natural checks and balance system
• There is a limit to the size of a population that
  the environment can support
• Deduction
• There is a struggle for existence
• Some live and some die

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Darwins Observations

• 2. Observation
• Organisms vary
• There are differences between individuals of the
  same specie
• These differences affect how well suited an
  organism is to its environment (fit or fitness)
• This is called adaptation
• Some individuals are better adapted to their
  environment than others because they have
  favorable variations
• Deduction
• In the struggle for existence, the less
  well-adapted individuals will tend to die
• Natural selection

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Darwins observations

• 3. Observation
• Much of the variation between offspring can be
  passed on to offspring
• It is heritable
• Deduction
• Better adapted individuals reproduce pass on
  their favorable characteristics
• Over the generations the characteristics of the
  population gradually change
• Evolution by natural selection

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Why do individuals within a specie show
variation?

• Genetic variations arise from gamete formation
  and fertilization
• Random assortment
• Crossing over
• Random fusion of male and female gametes during
  sex
• Mutations
• Not as powerful as sexual reproduction
• Mutations by be advantageous, harmful, or neutral
  
• Most mutations are neither harmful or useful
• Does this sound familiar?

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Evolution in Action

• Galapagos Finches
• Darwin visited the Galapagos Islands in 1835 and
  collected specimens of small birds (finches)
• Group of islands off the coast of Ecuador
• 14 species in all
• Darwin observed that the size and shapes of the
  beaks varied, as did their diet
• Further research from Peter and Rosemary Grant
  suggests a close relation between beak
  characteristic and diet

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Examples of natural selection

• Antibiotic resistance in bacteria
• Pesticide resistance in rats

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Antibiotic resistance in bacteria more evidence
for evolution

• Antibiotics were one of the great triumphs of
  medicine in the 20th century
• When they were first introduced, it was expected
  that they would offer a permanent method of
  controlling bacterial diseases
• However, there have been increasing problems of
  antibiotic resistance in pathogenic bacteria.

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The following trends have been established

• After an antibiotic is introduced and used on
  patients, bacteria showing resistance appear
  within a few years
• Resistance spreads to more and more species of
  bacteria
• Strains of bacteria appear that are resistance to
  more and more different antibiotics
• Called multiple resistance

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How?

• Antibiotic resistance is due to genes in
  bacteria and so it can be inherited
• Example of evolution by natural selection
• The evolution of multiple resistance has occurred
  in just a few decades.
• Due to
• Widespread use of antibiotics (humans and
  animals)
• Bacteria reproduce quickly (less than 1 hour)
• Populations of bacteria are HUGE, increasing the
  chance of a gene for resistance to form via a
  mutation
• If you want more info
• http//www.fda.gov/oc/opacom/hottopics/anti_resist
  .html

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Pesticide resistance in rats

• What are pesticides?
• Typically used by farmers
• Due to natural variation, some rats are
  unaffected (resistant) to the toxin
• They survive and reproduce, making a new
  population in which some or all members possess
  the genetic resistance
• New pesticide must be used
• The cycle continues

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Take away

• Illustrates how a population can adapt to its
  environment
• Illustrates how humans can be responsible for
  creating super-resistant creatures
• Why is this not an example of artificial
  selection?

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Flanders calls Homer an ape and makes a case for
evolution revolution in THE SIMPSONS episode
"The Monkey Suit"
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Exit Slip

• ½ sheet of paper name, date, period
• Title Exit slip
• 3 multiple choice questions
• 1 minute to answer each question before screen
  changes.

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Question1

• What is natural selection?
• The mechanism that increases the chance of
  certain individuals reproducing.
• The mechanism that leads to increasing variation
  within a population.
• The cumulative change in the heritable
  characteristics of a population.
• D. The mechanism that explains why populations
  produce more offspring than the environment can
  support.

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Question 2

• Which factors promote evolution in a species?
• I. Sexual reproduction
• II. Environmental change
• Overproduction of offspring
• A. I and II only
• B. II and III only
• C. I and III only
• D. I, II and III

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Question 3

• Natural selection is based on which of the
  following?
• I. Variation exists within populations.
• II. There is differential reproductive success
  within populations.
• Individuals must adapt to their environment.
• A. I only
• B. I and II only
• C. II and III only
• D. I, II and III