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Animal eyes

  1. May 12, 2007 #1
    I've noticed that most animals have irises that fill the entire eye,but humans do not. Does anyone have an explanation for this? Does our sclera provide us something unique? What's the adaptive function one way or the other?

    This question has been bugging me for weeks.

    Last edited: May 12, 2007
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  3. May 13, 2007 #2

    jim mcnamara

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  4. May 13, 2007 #3
    Thanks. In addition to being a psychologist, I'm a science fiction writer and in developing "alien" species, I need to have a good understanding of the adaptive benefits of various biological features.

    If anyone knows of a good reference, please let me know. I really do appreciate it.
  5. May 13, 2007 #4
    probably the best way to develop an alien species is to start by describing the environment they evolved in, and then look at animals in similar environments here on earth. that will give you a good place to start looking for adaptive traits.
  6. May 14, 2007 #5


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    One important factor to keep in mind when designing evolution-based critters is that evolution does not have a purpose, nor does any particular adaptation. While we like to say such things all the time, Arctic foxes did not evolve white fur "so that they could" have camouflage in the snow, and birds did not evolve flight "so that they could" escape predators.

    Evolution is more like throwing random stuff at a wall and taking the stuff that sticks.

    Rewind Earth's history and set it moving again, and foxes and birds might very well find completely different mechanisms allow them to survive.
  7. May 14, 2007 #6
    Thanks for the suggestions and reminders. I have started in several cases with the environments and worked from there. One species evolved on a rather colder world than ours. So they are on the average only about 1.5 meters tall. They have a lot of subcutaneous fat.

    Watching the series "Planet Earth" has simply astounded me with images of the diversity of earth. DaveC: you're completely right that try evolution again and plants and animals will likely develop differently, even given the same environment.

    I have also heard that humans may not be evolving biologically much anymore since our survival does not depend on biological adaptation, as compared to technological adaptation. I don't know if I agree, but it's an interesting concept.

    Again, I ask: is there any good reference book decribing how different features function based on evolution. I wonder if such a book exists.
  8. May 14, 2007 #7

    jim mcnamara

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    Try a google on convergent evolution, which is what you are asking about. PS: IMO, try to ignore wikipedia, because most articles there are changed/attacked by people who think evolution is bunk - for religious reasons usually under the guise of pseudo-science.

    Examples: Euphorbias and cactuses evolved in disjunct but similar similar environments and have similar adaptations - thorns, water-retaining tissues, few leaves, shallow root systems, etc.

    To my knowledge there is no book on the subject of convergent evolution.
    Another, not precisely identical term is parallel evolution, which is an older concept.
  9. May 14, 2007 #8
    The book you are asking for would be monstrous; descriptions of all the millions of different features for all the millions of different animals that exist or have existed on earth. That's why I said you should start with a certain environment, or a particular animal who may be similar in some way to the race you're trying to create. You have to narrow your field.
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