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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 Change over time Simpson’s couch gag http://www.jibjab.com/view/131239. What’s the evidence for evolution?. Charles Darwin

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IB Topic 5.4: Evolution

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  1. IB Topic 5.4: Evolution Individuals do not evolve, populations do

  2. What is evolution? • Evolution • Cumulative change in the heritable characteristics of a population • Change over time • Simpson’s couch gag • http://www.jibjab.com/view/131239

  3. What’s 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

  4. 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

  5. Some examples Many of these offspring die before they reproduce

  6. Darwin’s 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

  7. Darwin’s 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

  8. Darwin’s 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

  9. 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?

  10. 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

  11. Examples of natural selection • Antibiotic resistance in bacteria • Pesticide resistance in rats

  12. 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.

  13. 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

  14. 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

  15. 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 …

  16. 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?

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

  18. 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.

  19. 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.

  20. 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

  21. 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

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