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Natural Selection

Natural Selection

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Natural Selection

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  1. Natural Selection

  2. Warm up • Define the following words: • Population • Species p88

  3. Two interesting stories...

  4. The story of the peppered moth: 1850: mostly speckled; a few dark 1900: mostly dark; a few speckled 2000: mostly speckled; a few dark

  5. The story of the bacteria: • 2nd round of • same antibiotic: some die • 3rd round of • same antibiotic: • very few die • 1st round of antibiotics: most bacteria die

  6. What do these two stories have in common? On your Doodle sheet, in section 1A, THINK about this question and answer it. Now turn to your neighbors and share what you wrote (PAIR) SHARE:

  7. Given the phenomena of these two stories, what are some questions you could ask? On your doodle sheet, in space 1B, write down any questions you have (THINK) Talk with the rest of your table and compare questions. (PAIR) On your white board, write down your group’s favorite/best question. (SHARE)

  8. Driving Question Why/How do living things change over time? (record on your “keeping track of model” sheet)

  9. WHAT DO WE OBSERVE ABOUT POPULATIONS OF ORGANISMS? A. What happens to population sizes over time? If all offspring of two parent fish survive and reproduce, how many fish will there be after 4 generations?

  10. Another example: How many flies would there be by the end of one summer if all offspring of a mating pair survived and reproduced?

  11. Doodle Sheet 1C • What would happen if all offspring survived? • If you graphed the growth, what would the graph look like?

  12. OBSERVATION #1: Populations of organisms have the potential to grow exponentially. (record on model sheet) Graph of exponential growth:

  13. Is this what really happens? Are we overrun by fish… or flies… or any single species? What really seems to happen? In other words, what do we observe in real life? (doodle 1D) A species of grass Biomass of population A species of fish

  14. Yeast Sheep What is the pattern? How would you describe what populations really seem to do? Paramecium (a protist)

  15. OBSERVATION #2: Populations of organisms tend to stay relatively stable in size. (record on model sheet)

  16. Potential population growth in elephants Elephants are one of the slowest breeders on the planet. One female will produce 6 young over her 100 year life span. How many elephants could result from one male and one female in 750 years?

  17. 19,000,000 elephants!!!

  18. OBSERVATION #2: Populations of organisms tend to stay relatively stable in size. (record on your model sheet)

  19. With your partner, brainstorm a list of possible reasons why populations stay stable instead of continuing to increase exponentially. (record on Doodle Sheet 1E) Per.

  20. What do we call all these things collectively? RESOURCES! OBSERVATION #3: Populations are relatively stable in size due to limited resources in the environment. (record on model sheet)

  21. Lets play a game to see what happens when resources are limited!

  22. Even student #’s are DEER, odds are RESOURCES . Signs for resources: FOOD = both hands over belly, WATER = both hands over mouth, SHELTER = make a tent over head. Groups stand with backs to each other. Everyone picks a resource by making the appropriate sign. You must keep displaying your sign the whole time! On teacher’s signal turn and face each other. DEER must find someone showing the same resource on the other side. Each deer can only claim one resource. No changing once you turn around! If a deer finds a resource it can “reproduce”. The resource it caught becomes a deer for the next round. Resources not claimed stay a resource. Deer not able to find their resource die and become a resource for the next round. “OH DEER”

  23. 1. Was it always easy to be a deer in the game? Why or why not? DISCUSSION: record on Doodle Sheet 1F 2. When resources were limited, what did it feel like to be a deer?

  24. INFERENCE #1 Within populations of organisms there is a struggle to survive. (record on Model sheet)

  25. Sunflower Seed Activity • Follow the directions on the handout and answer the questions

  26. What do we observe when we compare individuals in a population? OBSERVATION #4 There is variation among organisms in a population. Variation naturally exists.(record on model sheet)

  27. Friendly Talk • Exit question: • Complete the friendly talk question before you leave class.

  28. Wormeaters

  29. What happened to: …the wormeater with the disadvantageous variation? (doodle sheet #2A) …the wormeater that got the most food? (doodle sheet #2B) Per.

  30. OBSERVATION #5: Individuals with advantageous variations have a better chance of surviving than those with less advantageous variations. (record on Model Sheet) OBSERVATION #6 Survival allows reproduction (record on Model Sheet)

  31. When the surviving wormeaters reproduce what kind of beaks did their offspring most have? (Doodle Sheet 2C) OBSERVATION #7: Many variations are inherited (in other words, offspring tend to resemble their parents). Record on model sheet

  32. What do you predict would happen to the # of individuals with the advantageousvariation in the next generation? (doodle 2D) INFERENCE #2: What about the # of individuals with the disadvantageous variations? (doodle 2D) The # of individuals with advantageous variations will increase in each new generation. The # with disadvantageous traits will decrease.(record on model sheet)

  33. What do you predict will happen to a species over many generations? (doodle 2E) INFERENCE #3: Over many generations the species changes, i.e. EVOLUTION occurs. (record on model sheet)

  34. EVOLUTION The Origin of Species E. Coleman 2010

  35. “Evolution”means change over time. The “Theory of Evolution” says: – Livingthings on Earth have changed over time. – Many species that once existed are now extinct. – Many species alive today were not here when life on Earth first formed. First thought of by the ancient Greeks (in 600 BC ) but they did not try to explain HOWit happened.

  36. First scientificattempt to explain how evolutionhappened came 2400 years later! In 1802 Jean LAMARCK proposed model:Evolution by Acquired Characteristics 1. More individuals are born than the environment can support-there is a struggle to survive. 2. Some individualsrespond by developing traitsthat give them a better chance to survive. 3. When these individuals reproducetheir offspring inherit their newly acquired, improved traitsand developthem even further. 4. Eventually ALLmembers of the species have the favorable trait. Jean Baptiste Lamarck 1744-1829

  37. Lamarck’s explanation of how the giraffe got its long neck: 1 2 3 • ALLearly giraffes had thesame(short ) necks. 2. As giraffe population increased there wasn’t enough food within reach for all so somebegan stretching their necks to reach food higher in the trees. – The more they stretched, the longertheir necks grew. 3. When they reproduced theypassed their longernecks on to their offspring who stretched their necks even more. – Eventually all giraffeshad long necks.

  38. Lamarck’smodel was quickly discarded. Scientists tried but could not find evidence to support his main ideas. All members of a species are NOTalike as Lamarck said. Great variation normally and naturallyexists within a species. Organisms cannotchange most of their basic physical traits at will, even if survival depends on It. They cannot “adapt” because they need to. For example giraffes cannotmake their necks grow longer by stretching them! 3. Organisms can change and improve somethings during their lifetimes (lifting weights to increase strength etc.) but these traits CANNOTbe passed to offspring. If this man wants his future children to have small noses will it help to get a nose job?? Is there anything he could do that might help?

  39. In1831, Charles Darwin (failed medical student, failed divinity student, avid beetle collector) began a 5 year journey on a small ship, the H.M.S. Beagle. 90’ long 75 people 5 years Around the world! Charles Darwin 1809-1882

  40. Purpose:survey coast of South America Darwin’s job:observe geology & biologyof the area. – Kept meticulous records of observations. His observations from theGalapagosIslandsled to his model of how evolution occurred. – Did NOT set out to develop a model, but couldn’t ignore what he saw. His curiosity drove him to try to explain what he had observed.

  41. Galapagos Islands are 600 miles off west coast of Ecuador (South America). Volcanic - first rose above the ocean surface less than 15 million years ago. Why is this special? 1) Life has been there a relatively short time (compared to billionsof years on the mainland!). 2) It developed in isolation from life on the mainland.

  42. Darwin was surprised to find species that clearly were closely related but that had distinct differences on different islands. High lush island Low, desert island

  43. He also discovered many species that were found nowhereelse on Earth, including the world’s only swimming lizard. It was hard for him to accept the prevailing belief that all of these specieshad been separately created.

  44. After returning to England Darwin spent 25more years gathering evidence. He also studied species selectively bred by humansfor desired traits - in particular, fancy pigeons and the many breeds of dogs created by 10,000 years of selective breeding.

  45. In 1859 Darwin published his model: On THE ORIGIN OF SPECIES by Means of Natural Selection At the time he was widely criticized and ridiculed.

  46. Darwin’s explanation of how evolution occurred: 1. More individuals are born in a species than the environment can support. There is a struggle to survive. 2. Within every species there is naturally variation. 3. Variations of some give them an advantage over others in the struggle to survive. 4.More of these individuals will survive and reproducethan will those with less favorable traits.

  47. 5. Many traits are passed from parents to offspring. 6. More individuals with favorable traits reproduce, so the # of individuals with favorable traits increases in each generation. The # with less favorable traits decreases. 7. Eventually the favorable trait becomes the most common form and over manygenerations (and usually millions of years) such differences accumulate until a newspecies results.

  48. Does it sound familiar??? Darwin called his model “Natural Selection”

  49. How Darwin explained the giraffe’s long neck: 2 3 1 • Ancestral giraffes had necks of various lengths. 2. When food became scarce, longer-necked individuals could reach more food sources so they survived in greater numbersthan those with shorter necks, many of whom starved and died. – more long necks survived, so more reproduced and passed the long-necked trait to their offspring. – each generation had more long and fewer short necks than the one before. 3. Eventually after many generations and millions of years ALL giraffes had long necks.

  50. Unlike Lamarck, the ideas in Darwin’s model were found to be consistent with observations and scientific evidence. In fact they continue to be supported by allevidence gathered in the 150 years since they were first published. This includes hundreds of thousands of experiments, studies, archeological finds, and facts.Scientists are so confident that Darwin’s model is correct that it is now called a TH EORY- The Theory of Evolution by Natural Selection.