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Darwin’s Theory of Evolution

Explore the key concepts of Darwin's Theory of Evolution, including natural selection, variation, and adaptation. Learn about the influential figures and evidence that support this well-tested explanation of the changes that occur in species over time.

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Darwin’s Theory of Evolution

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  1. Darwin’s Theory of Evolution

  2. What is Theory ?? • Most people think of it as a guess • “It’s just a theory.” • In Science a theory is not a guess. • A hypothesis is more like a guess than a theory • In Science a theory is a well tested and well supported explanation

  3. What is a Theory? • A well supported testable explanation of phenomena that have occurred in the natural world. • The Theory of Evolution

  4. Evolution • “Change over Time” • Geological Evolution • Change in non living characteristics of the earth over time • Examples = Climate & Continental Drift • Organic Evolution • Change in species over time • Change (in DNA) over time

  5. Evolution: Key Concepts • History: Darwin, Lamarck , Hutton, Lyell • Natural Selection : Survival of the Fittest • Evidence: • Fossils • Geographic Distribution of Species • Homologous Structures • Embryological Development • Evolution and Genetics • History of the Earth : Geologic Time Scale • Classification

  6. Can an Individual Evolve? • No! • Individuals are born with a set of chromosomes that determine their characteristics. • This set does not change • Individuals Develop • Populations EVOLVE

  7. Charles Darwin • Age 22 set sail on the H.M.S beagle (1831) • Chart coast line of South America and some pacific islands • Voyage took 5 years • Most significant observations were made on Galapagos Islands • He returned convinced that species evolve

  8. Voyage of the Beagle

  9. Survey made by the Beagle

  10. Current Survey

  11. Galapagos Island Finches

  12. Galapagos Island Tortoise

  13. Intermediate Shell Pinta Island Saddle-backed shell Hood Island Dome-shaped shell Isabela Island

  14. What Island does this Tortoise come from? Isabela

  15. Modern Evolution spurred from?? • Darwin’s Publications of …… • On the Origin of Species by means of Natural Selection • Published in 1858 • Nearly 25 years after the beagle returns home

  16. 6 Main Points of Darwin’s Theory • Variation • Overproduction • Competition • Adaptations • Natural Selection • Speciation

  17. Earlier Theories of Evolution • James Hutton (1785) • Earth is shaped by geological forces over millions of years not thousands of years • Charles Lyell (1831 ) • Writes about how the earth can be shaped (volcanoes , earthquakes) • Influences Darwin’s thinking • If the earth can change why can’t species

  18. Lamarck’s Theory of Evolution • Jean-Baptiste Lamarck (1809) • Selective use or disuse of organs, organisms acquired or lost certain traits during their life time. • Traits passed onto offspring • Over time this leads to change in a species DISPROVEN

  19. Jean-BaptisteLamarck believed… • Was based on the idea that individuals adapt during their own lifetimes and transmit traits they acquire to their offspring. • Offspring then adapt from where individuals left off, enabling evolution to advance. • As a mechanism of adaptation , Lamarck proposed that individuals increased specific capabilities by exercising them, while losing others through disuse.

  20. Lamarck’s Giraffe

  21. Lamarck vs. Darwin

  22. Back to Darwin’s Six Principles • Species tend to overproduce • This leads to competition • There is variation in a population • Some of these variations are positive adaptations • Natural selection means that those best adapted tend to survive and reproduce • This process of natural selection changes the gene pool

  23. Variation • Individuals in a species do not have identical characteristics • Darwin observed this fact but he could not explain the mechanisms that caused variability • Darwin did not know about DNA and Genetics

  24. Overproduction • Habitats have limited resources • Habitats can only support a limited number of individuals • Species tend to produce more offspring than can survive in a given environment

  25. Competition • Overproduction leads to competition • Members of a species compete for limited resources

  26. Adaptations • Adaptations are positive traits • That increases an individuals ability to survive in a given environment • Individuals with adaptations have higher fitness • They tend to survive and reproduce most successfully

  27. Natural Selection • The environment selects those individuals with the best adaptations to be the parents of the next generation • Those less fit cannot compete and they reproduce less (Survival of the Fittest) • Over many generations natural selection causes changes in the characteristics of species

  28. Speciation • New species arise from existing species through the process of natural selection

  29. Summary of Darwin’s Theory • Individual organisms differ from one another. • More offspring are produced than can survive. • Members of a species compete for limited resources. • Each unique organism has different advantages and disadvantages in the struggle for existence. • Individuals best suited to their environment survive and reproduce most successfully. • Species change over time. Natural selection causes changes in characteristics of species. New species arise, and other species disappear. • Species alive today have descended with modification from species that lived in the past. • All organisms on Earth are united into a single tree of life by common descent.

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