Anatomical homology

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  • Anatomical homology

    1. 1. anatomical homologyArgument #2 for Common Descent
    2. 2. anatomical homology: case forpig n’ arms A pigs forelimb consists of 3 large bones, the humerus, radius, and ulna. Our arms contain the same bones. This raises the question, why should the pig’s forelimb and my arm have hte same skeletal pattern. Darwin said these homologies (similarities) were best explained by this theory of descent from a common ancestor.
    3. 3. anatomical homology: case forpig n’ arms According to Darwin and modern evolutionary biologists, homologies are present in organisms because they inherited these structures from the ancestor they had in common. Humans and pigs both have similar bones in their forelimbs because we are related and descended from a common ancestor.
    4. 4. anatomical homology: case forpig n’ arms What actually gets passed from parent of offspring is the genetic information, which guides the making of the forelimb. Say we have two animals, A and B, which have homologous structures. The theory of Common Descent says that they were built by homologous genes. Also, the process of growing from an embryo to an adult (development pathway) are homologous, because they descended from a common ancestor.
    5. 5. anatomical homology: case forpig n’ arms According to neo-Darwinism, Natural Selection modifies genes over time. It also modifies the embryological processes that produce anatomical structures (like arms). Because of these modifications, related organisms have anatomical structures that are mostly similar, with a few differences.
    6. 6. anatomical homology: case forpig n’ arms Common Descent advocates, say that homologous anatomical structures originated in a common ancestor, and then were modified by natural selection. Also, they say that natural selection has modified the shapes and sizes of bones, and even eliminated some completely. Even still, you can see the ancestral pattern in those structures we recognize today as similar.
    7. 7. anatomical homology: case foras smart as a pig? It is not only in the skeletal system that homologies are seen. Similarities can also been seen in soft tissue structures like the brain and nervous system.
    8. 8. anatomical homology: case foronline resources http://evolution.berkeley.edu/evolibrary/article/0_0_0/lines_04
    9. 9. anatomical homology: a reply Harvard paleontologist Louis Agassiz, long before Darwin’s time, knew about the existence of homologous structures. He explained homologous structures as necessary because similar structures can solve similar functional problems. Cars and airplanes both have wheels, because they both have to move easily over horizontal surfaces. But this does not mean that airplanes evolved from cars.
    10. 10. anatomical homology: a reply RDK Thomas and WE Reif have developed an idea they call “the skeleton space”. What they mean by this, is that there are only a limited number of ways that geometric shapes and growing materials (like bones) can go together and still work well. This claims there are a limited number of skeletal patterns because of the functional requirements of organisms.
    11. 11. anatomical homology: a reply When 2 or more adult structures appear to by homologous, neo-Darwinist would say that they would have been built by homologous development (when the embryo becomes an adult) pathways and homologous genes. Contrary to this, biologists are learning that homologous structures can be produced by different genes and may follow different development pathways.
    12. 12. anatomical homology: a reply The wasp and fruit fly are an example of this. They both have body segments that are homologous. If they have the same body types because of a common ancestor, then they should have homologous genes and homologous development pathways. Contrary to this, the development of the bodies of some wasps is completely different than that of the fruit flies and even other wasps.
    13. 13. anatomical homology: a reply Another discovery that biologists have made, is that in many cases, the same genes help to produce different adult structures. Mouse - single lens camera eye
    14. 14. anatomical homology: a reply Another discovery that biologists have made, is that in many cases, the same genes help to produce different adult structures. Mouse - single lens camera eye
    15. 15. anatomical homology: a reply Another discovery that biologists have made, is that in many cases, the same genes help to produce different adult structures. Fruit fly - compound eye (with dozens of lenses)
    16. 16. anatomical homology: a reply Another discovery that biologists have made, is that in many cases, the same genes help to produce different adult structures. Fruit fly - compound eye (with dozens of lenses)
    17. 17. anatomical homology: a reply Another discovery that biologists have made, is that in many cases, the same genes help to produce different adult structures. Squid - single lens camera eye
    18. 18. anatomical homology: a reply Another discovery that biologists have made, is that in many cases, the same genes help to produce different adult structures. Squid - single lens camera eye
    19. 19. anatomical homology: a reply Each of these eyes develop along very different pathways and are wired differently from each other, but the same gene is involved in the development of all 3 eyes. The Neo-darwinism theory would say that non- homologous structures should be determined by non- homologous genes.
    20. 20. anatomical homology: a reply Biologists were shocked to discover this - that non- homologous structures (eyes) could be caused by homologous genes. Stephen Jay Gould called this discovery “unexpected under usual views of evolution”
    21. 21. anatomical homology: a reply Evolutionary biologists define homology as “similarity due to common ancestry”. Question: are there some similarities that are not due to common ancestry? Nearly all biologists would say, “Yes”.
    22. 22. anatomical homology: a reply Flippers of a whale and an ichthyosaur have similar shapes, but the whale is a mammal and the ichthyosaur was a reptile.
    23. 23. anatomical homology: a reply Flippers of a whale and an ichthyosaur have similar shapes, but the whale is a mammal and the ichthyosaur was a reptile.
    24. 24. anatomical homology: a replyAnother example is the forelimbs of a mole cricket and amole.
    25. 25. anatomical homology: a reply Biologists will tell you that these structures are not the result of common ancestors. And also that they arose separately on independent lines of descent.
    26. 26. anatomical homology: a replyresources 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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