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Organs and evolution

  1. Feb 26, 2016 #1
    Is it possible to classify all organisms which have eyes into one group and consider that they all have an evolutionary origin?
    I mean the eyes are used for the same function of seeing in all organisms.So it should be possible to classify them into a group on the basis of the function since eye is an analogous organ,right?
  2. jcsd
  3. Feb 26, 2016 #2

    Buzz Bloom

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    Hi Doc:

    I am not sure I understand what you are asking. Different kinds of eyes exist among different groups of species. For example, mammals, insects, and mollusks. These three kinds of eyes are very different form each other with respect to their respective architecture. It is reasonable to assume that the common ancestors of pairs of these groups did not have any eyes.

    Living creatures may be classified different ways. One way is by their evolutionary origins. Another way is by common characteristics. For ample, one might group all creatures that are aquatic as say "swimmers". This group would include fish and whales. While all fish have "swimmer" ancestors, whales do not.

  4. Feb 26, 2016 #3
    Hello Buzz,
    I'll be little specific.I do know that we classify organisms based on their evolutionary origin.The organs like eyes have different structures for different organisms.And I found in an encyclopaedia that organisms which possess eyes that are different in structure for each kind of organism do not have an evolutionary origin.But How? Isn't their similar function of using their eyes for seeing enough to say that they have an evolutionary origin?
    Furthermore,the encyclopaedia mentions that homologous organs(organs with different function but same structure like the forelimbs of birds,lizards,horses) and analogous organs(organs which have same function but different structure like the eyes of octopus,whales,humans) contribute in figuring out how evolution took place from simple to complex organisms.How is that possible?
  5. Feb 26, 2016 #4

    Buzz Bloom

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    Hi Doc:

    No, if you mean a common evolutionary origin. Eyes evolved independently multiple times.

    I cannot guess the context in your encyclopedia for this statement. If you can give the exact quote with its context, perhaps I can explain the apparent contraction.

  6. Feb 28, 2016 #5


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    There are some structures that serve as evolutionary markers. The spinal cord and the placenta are some examples.

    But there's also convergent evolution. Whales fins are an example. Whales didn't come directly from fish, but are mammals that developed fins independently.
  7. Feb 29, 2016 #6


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    Not necessarily. If the structure of one organ is significantly different than the structure of a similar organ in another species, then it is unlikely that the ancestor of both species had that organ. Once an organ is is created, it is very difficult for significant changes in its basic structure to occur. For example, the retina of vertebrates is inverted, meaning that the light sensing cells are behind the capillaries and neurons of the retina. But the retina of certain invertebrates like cephalopods is not inverted. The light sensing cells are in front of the other cells, and thus cephalopods have no blind spot like we vertebrates have.

    If the common ancestor of both vertebrates and cephalopods already had evolved eyes, then we would expect both lineages to have eyes with a similar basic construction. Perhaps one lineage might have built up a more complex eye, but that complexity would have been added to, or derived from, the existing structure of the eye. Changing from an inverted retina to a non-inverted retina or vice-versa is essentially impossible. It would have either required the loss of the organ's function over a long period of time while the necessary changes were evolved, or it would have required a sudden, drastic change. The former is very unlikely, as a loss of function would most likely be detrimental to the organism, and the latter is impossible as far as we know.

    If you haven't already, take a look at the wiki article on convergent evolution: https://en.wikipedia.org/wiki/Convergent_evolution

    The devil's in the details, as they say. The forelimbs of tetrapods are all variations on the same basic anatomical arrangement and structure. When I look at the forelimb of a whale, a horse, or a human, I can see a similar pattern in the layout and structure of the bones and other tissues (though this pattern isn't always obvious to the untrained eye). In addition, when we look at the fossil record, we can, in many instances, literally see the change to a particular limb over time as that particular lineage evolves. A striking example is the limbs of horses. We can see the evolution of the leg and feet from a five-toed design to the robust, single-toe design we see today. See the following link for more info on that. Pages 40 and 41 have diagrams of the feet of several different species leading up to modern horses. http://www.equinestudies.org/evolution_horse_2008/elsevier_horse_evolution_2008_pdf1.pdf

    The same is true of the limbs of whales and birds, I just don't have any links for them at the moment.

    The basic idea here is that if we look back into the fossil record, or even look around at many existing organisms, we can see a change in the complexity of organisms over time (or between different existing species). Reptiles are more complex, in general, than amphibians. Mammals are, generally, more complex than reptiles. The fossil record shows a gradual trend from less to more complex organisms. One way to see this trend is to look at how homologous and analogous organs change over time. Unfortunately I'm not sure how to explain why at the moment.

    Well, I'm sure I butchered that explanation enough for now. Someone correct me if I've made any glaring errors here.
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