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Darwin’s Tea Party

Darwin’s Tea Party. The Theory of Evolution by Natural Selection. Charles Darwin (1809-1882). Last update 8 Oct, 2009. Biological Evolution. Definition:

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Darwin’s Tea Party

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  1. Darwin’s Tea Party The Theory of Evolution by Natural Selection Charles Darwin (1809-1882) Last update 8 Oct, 2009

  2. Biological Evolution Definition: “Change in the genetic composition of a population during successive generations (due partly to natural selection) and resulting in the development of new species” (Wesbter’s).

  3. Biological Evolution The ancestors of the horse, for example, have undergone considerable change in physical size and proportions over the last 60 million years.

  4. Biological Evolution • The adult size, shape, bones, internal organs and many other physical and behavioural features have changed. • The original Eohippus was thus a different “type of animal” (species) than the present day horse (Equus)

  5. Evolution and Genes Such changes in body parts are the result of changes in genes. When nature “selects” the “fittest” for survival and reproduction, it is also selecting the fittest combination of genes to survive and reproduce. These come “packaged” in a creature’s body.

  6. Evolution and Genes • Thus Biological Evolution happens through the transmission of genetic characteristics from one generation to the next. • Individuals who are the most genetically “fit”, survive to reproduce (called natural selection or “survival of the fittest”) and pass on their fit characteristics.

  7. Evolution and Genes • During Darwin’s time not much was known about genetics. • But Darwin did know that variation existed. • That was enough to establish that in every species only those individuals that had favourable variations would be more fit and thus live on and reproduce.

  8. Evolution by Natural Selection • Natural selection is not the same as evolution • Natural selection is one cause of biological evolution. • It is like an “engine” that drives evolution on.

  9. Evolution by Natural Selection • “Natural selection” is a metaphor which Darwin compared to “artificial selection” (the breeding of plants & animals). • In “artificial selection”, humans “select” which individual plant or animal will reproduce. • In natural selection, “nature” does this “selecting”.

  10. Natural & Artificial Selection • In fact, Darwin begins his Origin by discussing the artificial selection (breeding) of pigeons. • In this example, we can see how three radically different looking breeds of pigeon (Pouter, Jacobin and Fantail) have been produced by artificial selection from the original Wild Rock pigeon.

  11. Natural & Artificial Selection Varieties of bananas produced by artificial selection

  12. Natural & Artificial Selection Note how all these dramatically different vegetables were created by artificial selection from an original ancestor.

  13. Natural Selection How does it work?

  14. Natural Selection is like a machine with 3 parts: 1. Variation The tendency for individuals in a species to differ slightly from their parents and from each other. 2. PopulationPressure the tendency for population growth to outstrip available resources 3. Deep Time The discovery that the earth (and life on it) was far older than had previously been thought.

  15. 1. Variation

  16. 1. Variation The tendency for individuals in a species to differ slightly from their parents and from each other.

  17. 1. Variation Will this be on the test? Variation among high school students

  18. 1. Variation You mean I was adopted? Variation within a family (not the dog – it’s a different species)

  19. 1. Variation They think were cute now But wait till they see their couch Variation between house cats (felis domesticus)

  20. I love peas 1. Variation The exact causes of variation were discovered only after Darwin’s death. The discovery was made by the Austrian monk Gregor Mendel, the father of modern genetics. Gregor Mendel (1823-1884)

  21. 1. Variation • One cause of variation is sex - the combining of the genetic material of male and female to create offspring. (Also called sexual recombination) • Another cause was mutation - accidents to the genetic material • Variation is NOT caused by population increase or by the environment or by use/disuse, etc…

  22. 1. Variation • Variation means there are different degrees of fitness among individuals in a population of the same species. • Some happen to be born with advantageous variations (giving them added fitness) and others not.

  23. 2. Geometrical Population Increase

  24. 2. Geometrical Population Increase The tendency for a population of any given species tends to outstrip the available resources necessary to keep it alive. As Darwin says, “More are born than can possibly survive”.

  25. 2. Geometrical Population Increase Want less poverty? STOP HAVING SEX!!! The “principle of population” was first expressed by the British political economist, Reverend Thomas Malthus. Thomas Malthus (1766-1834)

  26. 2. Geometrical Population Increase Malthus’ Concept of Geometric Population Increase (GPI) in the human world: In the human world, Malthus said, population tends to increase at a “geometric” rate while resources increase only at an “arithmetic” rate.

  27. 2. Geometrical Population Increase • Given this geometric rate of increase, part of the human population is bound to be poor or even die. • As Malthus states, • “...more will always be in want than can actually be supplied”.

  28. 2. Geometrical Population Increase • Darwin applied Malthus’ idea of geometric population increase to the entire living world. • He saw that it would lead to a “struggle for survival” continuously occurring between individuals in nature.

  29. 2. Geometrical Population Increase This “struggle for survival” would leave only the “fittest” individuals to survive (those with favourable variations) and reproduce Thus: GPI + V = NS (natural selection also called “the survival of the fittest”).

  30. 2. Geometrical Population Increase • By “fit” Darwin meant not just the “strongest” but those best adapted to the environment • These would tend to leave more offspring behind than the less fit.

  31. 3. Deep Time

  32. 3. Deep Time Deep time is the theory that the earth – and life on it – have been around for much, much longer than previously thought.

  33. 3. Deep Time • Given sufficient time (deep time) natural selection will have “weeded out” so many unfavourable variations and accumulated so many favourable variations that a new species will have developed from a previous ancestor.

  34. 3. Deep Time • Evolution by Natural Selection thus required millions of years to transform small changes into big ones. • But many naturalists believed that the Earth was only about 6,000 years old.

  35. 3. Deep Time The Irish Archbishop James Ussher (1581-1656) calculated the age of the earth according to what he believed the Bible indicated.

  36. 3. Deep Time I’m a YEC! • According to Ussher the universe began on Sunday, 23 October 4004 BC at 9:00 AM. • This was not enough time for evolution to have occurred Archbishop James Ussher (1581-1656)

  37. Geology Rocks! 3. Deep Time • But by the 19th century, the science of geology confirmed that the earth was actually millions of years old. • Key was geologist Charles Lyell’s book Principles of Geology which Darwin had read on the Beagle. Charles Lyell (1797-1875)

  38. 3. Deep Time • Thanks to Lyell and the science of geology, the earth – and life on it – were proven to be much older than anyone previously thought • For Darwin deep time was a key to acceptance of his evolutionary theory which required a huge time scale.

  39. 3. Deep Time: The Grand Canyon

  40. 3. Deep Time: The Grand Canyon 6000 feet deep at its lowest and 15 miles across at its widest. The Colorado river has cut into the Canyon, exposing almost 2 billion years of earth’s history. The Canyon’s geological structure shows it was made by a very, very long process of erosion by wind and water as well as volcanic activity and other geological processes.

  41. 3. Deep Time This chart gives us some idea of the scale of deep time. Note how recent is the arrival of Homo.

  42. 3. Deep Time • Another way of visualizing deep time • Note the many periods of glaciation • Note the changes in the shape and position of continents

  43. Summary: Natural Selection • Geometrical Population Increase (GPI)  causes “struggle for survival” (meaning only some individuals will live and reproduce) • Variation (V) causes differences in fitness b/w individuals THUS: GPI + V = “survival of the fittest” (natural selection)

  44. Summary: NS + Deep Time Natural Selection + Deep Time = Biological Evolution

  45. Cast of characters Charles Darwin (1809-1882)Founder of theory of evolution by natural selection Charles Lyell (1797-1875)Discoverer of ‘deep time’ Thomas Malthus (1766-1834)Articulates the ‘principle of population’ Gregor Mendel (1823-1884)Founder of science of genetics

  46. The End Written & Directed by Gabriel Tordjman

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