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IB Topic 5.4: Evolution


IB Topic 5.4: Evolution Individuals do not evolve, populations do What is evolution? Evolution Cumulative change in the heritable characteristics of a population ... – PowerPoint PPT presentation

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Title: IB Topic 5.4: Evolution

IB Topic 5.4 Evolution
  • Individuals do not evolve, populations do

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

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

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

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
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

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

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

Why do individuals within a specie show
  • Genetic variations arise from gamete formation
    and fertilization
  • Random assortment
  • Crossing over
  • Random fusion of male and female gametes during
  • 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?

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

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.

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
  • Strains of bacteria appear that are resistance to
    more and more different antibiotics
  • Called multiple resistance

  • 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
  • Bacteria reproduce quickly (less than 1 hour)
  • Populations of bacteria are HUGE, increasing the
    chance of a gene for resistance to form via a
  • If you want more info
  • http//www.fda.gov/oc/opacom/hottopics/anti_resist

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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

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

Flanders calls Homer an ape and makes a case for
evolution revolution in THE SIMPSONS episode
"The Monkey Suit"
Exit Slip
  • ½ sheet of paper name, date, period
  • Title Exit slip
  • 3 multiple choice questions
  • 1 minute to answer each question before screen

  • 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

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

Question 3
  • Natural selection is based on which of the
  • 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
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