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Embryology

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Embryology

  1. 1. embryology Argument #4 for Common Descent
  2. 2. embryology: case for Embryology is the study of the development and formation of embryos. One of Darwin’s arguments for Common Descent is based on the similarity of embyros of different organisms. Darwin writes, “by far the strongest single class of facts in favour of” his theory of Common Descent.
  3. 3. embryology: case for Darwin noticed similarities in the embryos of vertebrate animals especially during the embryo’s earliest stage of development. Because of the similarities he concluded 2 things.
  4. 4. embryology: case for 1. It established that organisms had descended from a common ancestor. He thought that embryos of modern vertebrates are similar because they evolved from an ancestral form that had many of the embryonic features of the modern vertebrates.
  5. 5. embryology: case for 2. Darwin thought the observable similarities in different embryos revealed the ancestors to these organisms would have looked like. Darwin said that the embryo “is the animal in its less modified state”
  6. 6. embryology: case for Ernst Haeckel was a German embryologist and he popularized Darwin’s 2 main ideas about embryology. He produced a set of influential drawings showing that the embryos of various classes of vertebrates were very similar during their earliest stages of development.
  7. 7. Haeckel’s Embryo’s
  8. 8. embryology: case for Modern evolutionary biologists have modified Darwin’s and Haeckel’s ideas. They no longer think that embryos reveal the adult form of their evolutionary ancestors. Some scientists now think that embryos tell us what the embryos of their evolutionary ancestors might have looked like.
  9. 9. embryology: case for online resources http://www.nyu.edu/projects/fitch/courses/evolution/html/ebryology.html#LectureNotes http://www.pbs.org/wgbh/evolution/library/04/2/l_042_02.html http://www.nyu.edu/projects/fitch/courses/evolution/html/embryology.html
  10. 10. embryology: a reply Critics of the argument from embryology agree that common descent might be a reasonable idea, if the embryos really were similar in their earliest stages of development. But, according to most embryologists, they are not.
  11. 11. embryology: a reply Adam Sedgwich, of Cambridge University, in 1894, challenged Darwin’s claims. The embryo’s, of even closely allied animals, such as chickens and ducks, display specific differences very early in development. You can tell the difference between a duck and a chicken on the second day of development.
  12. 12. embryology: a reply If the early embryos are so different, then why did the erroneous claim become so popular? Critics states 2 reasons: 1. Haeckel’s drawings misrepresented the features of the embryos, he drew them incorrectly, in order to match Darwin’s theory. 2. Darwin and Haeckel both left out the earliest stage of development. This is critical because the embryos are quite different at this stage.
  13. 13. embryology: a reply Haeckel’s drawings became very widespread. They can be found in many biology textbooks today, with the claim that the vertebrate embryos are most similar in their earliest stages.
  14. 14. embryology: a reply In 1997, an international team of scientists, led by embryologist Michael Richardson, compared Haeckel’s drawings to photographs of actual embryos at various stages of development. They discovered that Haeckel distorted the evidence. Richardson told the journal Science, “it looks like it’s turning out to be one of the most famous fakes in biology.”
  15. 15. Richardson’s Picture Comparison
  16. 16. embryology: a reply Stephen Jay Gould wrote, “I think we have the right to be both astonished and ashamed by the century of mindless recycling that has led to the persistence of these drawings in a large number, if not majority, of modern textbooks.”
  17. 17. embryology: a reply resources Evolution Exposed by Roger Patterson Speciation - page 57-67 Homology - page 68-72 Fossils (transitional) - page 73-74 Molecular Homology - page 74-75 Embryology - page 95-96 Refuting Evolution by Jonathan Sarfati The Politically Incorrect Guide to Darwinism and Intelligent Design by Jonathan Wells

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