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Understanding Natural Selection: How Evolution Works

Explore the concept of natural selection and how it drives evolution. Learn about the mechanisms of overproduction, variations, competition, selection, and environmental change. Discover the role of Charles Darwin and his observations on the Galapagos Islands. This informative guide provides insights into the process that shapes species over time.

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Understanding Natural Selection: How Evolution Works

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  1. Natural Selection …how evolution works.

  2. Natural selection is… • Natural selection says that the organisms best suited to the environment will live to reproduce while other organisms that are not as well suited will die.

  3. What does Natural Selection mean? Organisms that are better adapted to their environment tend to survive longer. (Nature has “selected” them to survive because they have more useful traits.) The survivors tend to produce more offspring than the less well adapted, so those useful genetic traits become more common, until, after many generations, all of that species has the useful trait. This process of change over time is called evolution

  4. Natural Selection Darwin noted 5 “mechanisms” that drove natural selection: • Overproduction • Variations • Competition • Selection • Environmental Change

  5. Overproduction Simply stated: more offspring are produced than can survive in a species.

  6. Variations • These are differences among individuals in a population.

  7. Competition • Competition: Individuals will compete to survive and reproduce. • Indirect Competition: Using the same resources. Zebras and Wildebeast eating the same grass. • Direct Competion: Hurting or killing another organism to obtain a resource. Lions and Hyenas fighting over a kill, or males fighting for mates. ->

  8. Selection • Different traits (variations) make organisms more or less likely to survive. • The environment “selects” organisms (lets them live and reproduce) based which have the most useful variations. - Organisms that are better suited to live in an environment will survive, reproduce and pass on their traits. - Over time, this can lead to changes in a species, aka, evolution

  9. Selection A real example, the Arctic Fox

  10. Sometimes there are beneficial genetic behaviors as well. Alan?

  11. Environmental Change Changes in the environment can affect the whether certain individuals in a species survive. Pre Industrial Revolution Post Industrial Revolution Environmental changes can make other traits more useful (so they become dominant) or they might wipe out a species entirely if there is not a variation that can survive the change.

  12. “When the monster came, Lola, like the Peppered Moth, remained motionless and undetected. Harold, of course, was immediately devoured.”

  13. Natural selection at work… THEN…

  14. THEN…

  15. Background (normal) Extinction vs. Mass (holy crud!) Extinction

  16. Mass Extinction…

  17. A Little History Darwin, Evolution, and Natural Selection

  18. Charles Darwin I’m a naturalist. • Came up with the idea that evolution happens through natural selection. • Is credited with being the father of evolution

  19. Darwin’s Journey • Accompanied the captain of the H.M.S. Beagle on a journey around the world. • Observed many plants and animals. • Observed some very interesting (weird) animals in the Galapagos Islands that helped him discover the process of natural selection. Iguanas don’t swim. Islands provide environments you can’t leave. You must adapt to if you are an animal.

  20. Darwin’s Discovery • Noticed that animals seemed to be specially adapted to the places that they lived.

  21. He especially noticed this in a type of bird, a finch, that lived in the Galapagos Islands, but had weird beaks. • All of their beaks were specifically suited to the type of food that they ate.

  22. Aha! • Darwin determined that the finches that had the beaks that got the most food lived longer and reproduced more than the ones that didn’t get as much food. • That led him to his idea of natural selection, or ”survival of the fittest,” (those best suited to the environment are likeliest to survive, reproduce, and pass on those traits.)

  23. Darwin Thought.. • That the finches had adapted to being on each of the islands because each island had different food • Eventually these finches lived apart from each other for so long and changed so much that they could no longer breed with each other. That is what makes a new species!

  24. Darwin’s Picture of how he thought the finches were related

  25. Cladogram- a branching diagram that represents the proposed evolutionary history of a species

  26. Taxonomy – how we classify things

  27. When he got home… • Married his cousin • Was afraid to publish his findings, thought people, like his wife, would be upset with him. • Studied more of his idea by watching pigeons. • Finally published his book On the Origin of Species in 1858 because another scientist (Alfred Wallace) was going to beat him to it.

  28. Darwin • In 1859, Darwin published his findings in a book titled “The Origin of Species”

  29. Darwin’s idea had two parts: • 1. Descent with modification- animals and plants on the earth today are just changed versions of what was here long ago (new animals don’t just come to life out of nowhere).

  30. Darwin’s Idea had two parts: • 2. Modification by natural selection- states how the evolution occurs. Basically those who are most suited to the environment pass on their DNA, those that die…don’t.

  31. Lamark Proposed First Hypothesis • Thought giraffes had long necks because they stretched them to reach leaves. • Was proven to be wrong

  32. Why Lamark Was Wrong • DNA is passed to offspring, not acquired traits.

  33. Evolution

  34. Fossil Record Embryos Structures Homologous Analogous Vestigial 4.Geological 5.Cellular Evidence 6.Experiments/ Artificial selection 7. DNA Evidence for Evolution

  35. Fossil Record

  36. Fossil Record

  37. Fossil Record Above left, the Cretaceous snake Pachyrhachis problematicus clearly had small hindlimbs. The drawing at right shows a reconstruction of the pelvis and hindlimb of Pachyrhachis

  38. Embryos

  39. Homologous Structures- Structures that are similar due to common ancestry.

  40. Analogous Structures Shows that animals in same habitat tend to develop similar features due to natural selection.

  41. Geological Evidence • Law of superposition • Dating of rocks

  42. Vestigial Structures- Structures that used to function, but no longer have a purpose. • Tailbones in People • Appendix in People • Ear muscles that no longer function in people • Hip bones in Snakes

  43. Geological Evidence Common ancestor was on a supercontinent; decendents moved with the plates.

  44. Cellular Evidence

  45. Experiments/Artificial Selection

  46. DNA Cladogram- a branching diagram that represents the proposed evolutionary history of a species

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