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Natural Selection

Explore the concept of natural selection and how organisms with favorable traits have a higher chance of survival and reproduction. Learn about the four steps of natural selection and examples of its effects in various populations and environments.

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Natural Selection

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  1. NaturalSelection

  2. Survival of the Fittest? • Is this what Darwin meant?

  3. Natural Selection The process by which organisms with favorable traits survive and reproduce at a higher rate than organisms without the favorable trait

  4. Natural Selection • Organisms - • Better able to survive and reproduce in an environment • More likely to pass their traits on to future generations • Traits improve chances of survival or reproduction • Likely to accumulate in a population after several generations • Traits are “selected”

  5. NaturalSelection in Four Steps • Overproduction • Genetic Variation • Struggle to Survive • Successful Reproduction

  6. Overproduction • More individuals are born than will become adults.

  7. Genetic Variation • Individuals • Not exactly the same • Have own set of traits (size, color and the ability to find food) • Some traits more likely to survive and reproduce • Other traits less likely for survival and reproduction

  8. Struggle to Survive • Environment • Not able to support all of the individuals born • Individuals • Killed by other organisms • Do not find mates • Only some will become adults and reproduce

  9. Successful Reproduction • Individuals and Their Environment • Well Adapted • More likely to survive • More likely to reproduce • Traits likely to be selected • Not Well Adapted • More likely to die early • Have few offspring • Traits less likely to be selected

  10. Survival of the Fittest • Key to Natural Selection – Heredity • Traits passed from one generation to the next • No reproduction – genes will not be passed on • Characteristics • Survival vs. Reproduction • Peacock’s bright feathers • Flower’s color

  11. Natural Selection in Action • Population • Changes in response to its environment • Tends to be well adapted to its environment • Environment changes too quickly • Some organisms may not survive • Only organisms with certain traits are able to survive and reproduce in the new environment

  12. Natural Selection in Action • Examples • Insecticide Resistance • Adaptation to Hunting • Industrial Melanism • Butterfly Story

  13. Insecticide Resistance

  14. Adaptation to Hunting • Tusks of Male African Elephant • 1930 – 99% born with tusks • Present – as few as 85% have tusks • Males with tusks killed therefore could not reproduce • Males without tusks able to reproduce • If this trend continues tuskless elephants will outnumber elephants with tusks • Males did not lose tusks, tuskless elephants were able to pass on their traits

  15. Industrial Melanism

  16. How has predation influenced evolution? Adaptations to avoid being eaten: Spines (cactii, porcupines) Hard shells (clams, turtles) Toxins (milkweeds, dart frogs) Bad taste (monarchs) Camouflage Mimicry Aposematic colors

  17. Quiz • Adaptation and Survival • How does this characteristic help with survival or successful reproduction • Stripes on a tiger – • Song of a bird – • Ears of an elephant – • Poison of a rattle snake – • Glow of a firefly – • Antler of a male deer – • Bright flowers of a rose –

  18. Quiz • Adaptation and Survival • How does this characteristic help with survival or successful reproduction • Stripes on a tiger - • Camouflage for hunting • Song of a bird – • Attracts mate/defends territory

  19. Quiz • Ears of an elephant – • Prevent overheating • Poison of a rattle snake – • Capture of prey, protection from predators

  20. Quiz • Glow of a firefly – • Attracts mate • Antler of a male deer – • Defends right to mate

  21. Quiz Bright flowers of a rose – • Attract pollinators

  22. VOCABULARY REVIEW • EVOLUTION – CHANGE OVER TIME • NATURAL SELECTION - INDIVIDUALS BETTER ADAPTED TO THE ENVIRONMENT ARE ABLE TO SURVIVE & REPRODUCE. • A.K.A. “SURVIVAL OF THE FITTEST”

  23. 3 ISOLATING MECHANISMS…….. • BEHAVIORAL ISOLATION- CAPABLE OF BREEDING BUT HAVE DIFFERENCES IN COURTSHIP RITUALS (EX. MEADOWLARKS) • GEOGRAPHICAL ISOLATION – SEPARATED BY GEOGRAPHIC BARRIERS LIKE RIVERS, MOUNTAINS, OR BODIES OF WATER (EX. SQUIRREL) • TEMPORAL ISOLATION – 2 OR MORE SPECIES REPRODUCE AT DIFFERENT TIMES.

  24. Table 23.1a

  25. 3.How did tortoises and birds differ among the islands of the Galapagos? • Each island had its own type of tortoises and birds that were clearly different from other islands

  26. Galapagos Turtles

  27. 5. Geologists: Hutton and Lyell • Fundamentalists said that the earth was around 6000 years old • Hutton and Lyell argued that the earth is many millions of years old b/c • layers of rock take time to form • processes such as volcanoes and earthquakes shaped the earth and still occur today

  28. LamarkTheory of acquired characteristics • Lamark said organisms acquired traits by using their bodies in new ways • These new characteristics were passed to offspring • Lamark was totally wrong!

  29. 9. Artificial Selection • nature provides variation, humans select variations that are useful. • Example - a farmer breeds only his best livestock

  30. 10. Natural Selection • The traits that help an organism survive in a particular environment are “selected” in natural selection

  31. 11. Natural Selection and Species Fitness • Overtime, natural selection results in changes in the inherited characteristics of a population. • These changes increase a species fitness (survival rate)

  32. Descent with Modification • Each living species has descended with changes from other species over time

  33. Summary of Darwin’s Theory 1. Organisms differ; variation is inherited 2. Organisms produce more offspring than survive 3. Organisms compete for resources 4. Organisms with advantages survive to pass those advantages to their children 5. Species alive today are descended with modifications from common ancestors

  34. 13. Evidence of Evolution • Fossil Record • Geographic Distribution of Living Species • Homologous Body structures • Similarities in Embryology

  35. Evidence of Evolution Fossil Record provides evidence that living things have evolved Fossils show the history of life on earth and how different groups of organisms have changed over time

  36. Relative vs. Absolute Dating

  37. Relative Dating • Can determine a fossil’s relative age • Performed by estimating fossil age compared with that of other fossils • Drawbacks – provides no info about age in years

  38. Absolute dating • Can determine the absolute age in numbers • Is performed by radioactive dating – based on the amount of remaining radioactive isotopes remain • Drawbacks - part of the fossil is destroyed during the test

  39. 13. Evidence of Evolution • Geographic Distribution of Living Species Similar animals in different locations were the product of different lines of descent

  40. 13. Evidence of Evolution Turtle Homologous Body Structures • Structures that have different mature forms but develop from the same embryonic tissues e.g. Wing of bat, human arm, leg of turtle Alligator Bird

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