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Thread: Evolution Question

  1. #1 Evolution Question 
    Forum Freshman asxz's Avatar
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    What was the evolutionary advantage of having eyes facing foward? I know that it helps with depth perception, but it must have been a really good reason for a whole race to change like that. If having good depth perception is a good enough reason, then why didn't birds and that evolve down the same track? Does depth perception overpower the need for observational awareness, or is it just that humans needed it more?


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  3. #2 Re: Evolution Question 
    Universal Mind John Galt's Avatar
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    Quote Originally Posted by asxz
    What was the evolutionary advantage of having eyes facing foward? I know that it helps with depth perception, but it must have been a really good reason for a whole race to change like that. If having good depth perception is a good enough reason, then why didn't birds and that evolve down the same track? Does depth perception overpower the need for observational awareness, or is it just that humans needed it more?
    You try jumping from bough to bough in the trees without good stereo vision. Mortatlity rate will shoot up.

    As for birds, have you never looked at an owl?


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    Forum Cosmic Wizard paralith's Avatar
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    But, what types of birds amongst birds have forward facing eyes? Amongst non-primates, what mammals have forward-facing eyes? Predators. Owls, raptors, felines, canines, ursines. Branch-to-branch leaping can definitely be helped by stereo vision, but squirrels are relative masters of tree-living and their eyes are very much on the sides of their heads.

    One hypothesis is that ancestral primates first developed stereo vision in order to hunt for insects. Our ancestors were small and arboreal, and thus were probably solitary, nocturnal, insectivores. And probably small berries and flower buds when available, but insects would be the staple. All modern prosimians that are of that size have this same feeding ecology.
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    All good points paralith, but you still never see a monkey with an eye patch. :wink:
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  6. #5 Re: Evolution Question 
    Forum Cosmic Wizard spuriousmonkey's Avatar
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    Quote Originally Posted by asxz
    What was the evolutionary advantage of having eyes facing foward?
    The ones with the eyes facing backwards tended to bump into things and fall into holes, or walk into predator's mouth. And if not that, then prickly bushes.
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  7. #6 Re: Evolution Question 
    Universal Mind John Galt's Avatar
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    The ones with the eyes facing backwards became accountants.
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  8. #7  
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    Interesting question, asxz. Interesting replies. Still a mystery then.
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  9. #8  
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    why would something that has scientific explanations be called a mystery?
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  10. #9  
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    Paralith is absolutely correct. Predators evolve stereo vision. The opposite though, is that those animals who remain prey, keep their eyes to the side. What they lose in stereo vision they gain in peripheral vision. A deer, for example, can see almost all around its body. It has no stereo vision, but it does not need stereo. What it needs is to see the lion creeping up behind it. And that it can do with eyes at the side of its head.
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  11. #10  
    Forum Cosmic Wizard paralith's Avatar
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    Quote Originally Posted by John Galt
    All good points paralith, but you still never see a monkey with an eye patch. :wink:
    I've never seen a squirrel with an eye patch either.

    Ever seen the way they leap? I've witnessed some impressive feats of derring do by squirrels determined to get to our bird feeder.
    Man can will nothing unless he has first understood that he must count on no one but himself; that he is alone, abandoned on earth in the midst of his infinite responsibilities, without help, with no other aim than the one he sets himself, with no other destiny than the one he forges for himself on this earth.
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    why would something that has scientific explanations be called a mystery?

    Because something with four "scientific" (just-so stories) "explanations, is, by definintion, a mystery.
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    Vexer, testable hypotheses are not just-so stories. We can look in the natural world and see, of the animals that have forward facing eyes, what is their mode of subsistence? Forms of predation where gauging distance is important. Predatory mammals like felids and canines that have to judge how far and how fast they have to run to catch prey. Predatory birds like owls and raptors that have to judge how far away a prey item is and how quickly they need to descend to catch it.

    Early primates were most likely insectivores, and we know that because of the primitive primates that exist today and the fossils of early primates that we have discovered. A lot of animals that eat insects also have forward facing eyes but not all of them, so this could be evidence against insectivory requiring binocular vision. However we also know that primates unlike other mammals have a grasping hand that can be used to grab bugs, and thus they require hand-eye coordination. To successfully use hand-eye coordination with fast moving prey you need to judge distance - where is the food relative to my hand, where is my hand relative to my my mouth. We can empirically test the efficacy of hand-eye coordination in people by having them perform difficult tasks with either both eyes open or with one eye closed. We can even test it in captive primates.
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  14. #13  
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    So there arenít competing theories?
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    question : did any non-avian predatory dinosaurs ever have stereoscopic vision ?
    "Reality is that which, when you stop believing in it, doesn't go away." (Philip K. Dick)
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    Quote Originally Posted by Vexer
    So there arenít competing theories?
    One was brought up in this thread, that stereoscopic vision is advantageous for moving in trees. The problem is that there are lots of arboreal animals, including ones that leap as much as any monkey, that do not have stereoscopic vision, like squirrels. However you could run tests on squirrels and monkeys to see if one can leap more accurately than other; if monkeys are more accurate, perhaps the stereoscopic vision could be an advantage; if monkeys and squirrels seem to be equally accurate, then it probably isn't.
    Man can will nothing unless he has first understood that he must count on no one but himself; that he is alone, abandoned on earth in the midst of his infinite responsibilities, without help, with no other aim than the one he sets himself, with no other destiny than the one he forges for himself on this earth.
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    You would also need to take into account the consequences of an inaccurate jump. If the clawed limbs of a squirrel are more effective at gaining purchase from a near miss than the grasping limbs of a monkey, then the squirrel doesn't need such good distance judgement. If the monkey is more likely to be injured in a fall than a squirrel, then the monkey needs superior distance judegement to stand an equal chance of survival.
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  18. #17  
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    Quote Originally Posted by John Galt
    You would also need to take into account the consequences of an inaccurate jump. If the clawed limbs of a squirrel are more effective at gaining purchase from a near miss than the grasping limbs of a monkey, then the squirrel doesn't need such good distance judgement. If the monkey is more likely to be injured in a fall than a squirrel, then the monkey needs superior distance judegement to stand an equal chance of survival.
    But then that makes you wonder why monkeys lost claws. (Which some modern species then re-developed, also for as yet unknown reasons.)
    Man can will nothing unless he has first understood that he must count on no one but himself; that he is alone, abandoned on earth in the midst of his infinite responsibilities, without help, with no other aim than the one he sets himself, with no other destiny than the one he forges for himself on this earth.
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    birds without stereoscopic vision are actually quite good at estimating the position of stationary objects using paralax, and hence can fly through quite narrow gaps in say a hedge or fence
    it's a different story, though, when it comes to judging your position against moving objects using this method, as is evidenced by birds flying into cars by keeping a constant angle with the car during flight - this method enables them to stay on course if judged against distant objects, but doesn't work very well for avoiding nearby ones

    so maybe predators require stereoscopic vision to accurately estimate distance to a moving prey, whilst vegetarian tree-dwellers only have relatively stationary branches to contend with
    vegetarian monkeys and apes are the exception here, but as paralith said, this is probably due to them having insectivorous ancestors
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  20. #19  
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    Quote Originally Posted by paralith
    But then that makes you wonder why monkeys lost claws. )
    It was a pre-adaptation to facilitate nail biting finales to Science Forum debates.
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  21. #20  
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    Squirrels versus monkeys.

    Perhaps both need steroscopic vision, but squirrels require good peripheral vision for detecting predators even more. Sometimes one advantage (distance vision) is sacrificed to maximise another (seeing a bird of prey attacking from behind).
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  22. #21  
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    There are multiple solutions to the same problem.

    So there is no problem.

    And history will determine what is possible or not.
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    Quote Originally Posted by spuriousmonkey
    There are multiple solutions to the same problem.

    So there is no problem.

    And history will determine what is possible or not.
    If "the problem" is not knowing why humans have stereoscopic vision, then having multiple plausible explanations certainly does not solve the problem. If you're trying to solve a murder mystery and determine that any of four people might be the killer, would you consider that a resolution and announce that the mystery is solved?
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  24. #23  
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    Quote Originally Posted by marnixR
    question : did any non-avian predatory dinosaurs ever have stereoscopic vision ?
    Pachycephalosauria also had stereoscopic vision
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    but were not predators ?
    "Reality is that which, when you stop believing in it, doesn't go away." (Philip K. Dick)
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  26. #25  
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    Quote Originally Posted by marnixR
    but were not predators ?
    Correct, current paleobiological thinking is that the Pachycephalosauria were herbivores
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  27. #26  
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    hm - curiouser and curiouser
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    My knowledge of pachycephalosaurs ends at grade school picture books of two of them smashing their heads together; what's the paleontological assessment of this behavior?
    Man can will nothing unless he has first understood that he must count on no one but himself; that he is alone, abandoned on earth in the midst of his infinite responsibilities, without help, with no other aim than the one he sets himself, with no other destiny than the one he forges for himself on this earth.
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  29. #28  
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    Quote Originally Posted by paralith
    My knowledge of pachycephalosaurs ends at grade school picture books of two of them smashing their heads together; what's the paleontological assessment of this behavior?
    Looong outdated... evidence shows no signs of head butting behavior. The necks have been shown to have had an s shape not out straight and the craniums show not evidence of trauma. Paleontologists in general think that aggressive displays and possible flank-butting may have occurred
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    Fossilized collagen fibers found on top of the domes suggest that scales or horns covered the head. It has been proposed that it bore a colorful display.

    To me, the idea of two such enormous animals butting heads like rams has always been a bit difficult to believe.
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  31. #30  
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    Quote Originally Posted by Scifor Refugee
    Quote Originally Posted by spuriousmonkey
    There are multiple solutions to the same problem.

    So there is no problem.

    And history will determine what is possible or not.
    If "the problem" is not knowing why humans have stereoscopic vision, then having multiple plausible explanations certainly does not solve the problem. If you're trying to solve a murder mystery and determine that any of four people might be the killer, would you consider that a resolution and announce that the mystery is solved?
    We have stereoscopic vision because a direct ancestor had it and developmental constraints did not allow for a shift in this feature.

    No rocket science needed.
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    Quote Originally Posted by spuriousmonkey
    We have stereoscopic vision because a direct ancestor had it and developmental constraints did not allow for a shift in this feature.
    Wow, no shit. That's just another way of saying that we have it. Kind of like answering the question "Why is Bob at the mall?" with "Bob is at the mall because he traveled to the mall and has not yet left the mall."
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  33. #32  
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    Quote Originally Posted by spuriousmonkey
    We have stereoscopic vision because a direct ancestor had it and developmental constraints did not allow for a shift in this feature.
    That's not necessarily correct either, though. Perhaps our ancestors developed it and we haven't lost it because it is still advantageous to have it?
    Man can will nothing unless he has first understood that he must count on no one but himself; that he is alone, abandoned on earth in the midst of his infinite responsibilities, without help, with no other aim than the one he sets himself, with no other destiny than the one he forges for himself on this earth.
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  34. #33  
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    yeah, how lose it?

    Restructure your entire skull because you don't fancy stereoscopic vision???

    Why do we suddenly all have problems with the fucking obvious.

    Stereoscopic vision was present in the ancestral lineage. And it continued to be beneficial for most the lineages derived from it.

    Moving around the eye sockets in your skull just because someone on an internet forum thinks is beneficial is a moronic concept.

    There will never be major changes to a winning design. Or at least the most crucial aspects of the winning design. Due to developmental constraints and adaptive aspects.

    That's why all rodents still have a diastema and two upper and two lower continuously growing incisors that sharpen themselves.

    You might start speculating on whether it would be nicer for rodents to have premolars under certain conditions, but they don't come back because we think it would be cool.

    In fact when people think like that, they don't understand evolution at all, or at least don't get the most important aspect of evolution. It is a historic process that is governed by developmental constraints.

    and that is all there is to it.
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  35. #34  
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    Quote Originally Posted by spuriousmonkey
    Moving around the eye sockets in your skull just because someone on an internet forum thinks is beneficial is a moronic concept.
    Spurious, I'm not sure what your problem is, but somehow I don't think anyone is suggesting that evolution ought to be doing what someone on a forum thinks it ought to be doing. There's no need to be so caustic. We're offering alternative possibilities other than the single one you seem so sure is the only way it could have happened.

    yeah, how lose it?

    Restructure your entire skull because you don't fancy stereoscopic vision???
    Indeed, the same way our ancestor's skull was entirely restructured to allow for stereoscopic vision in the first place. Clearly such restructuring is possible.

    Why do we suddenly all have problems with the fucking obvious.

    Stereoscopic vision was present in the ancestral lineage. And it continued to be beneficial for most the lineages derived from it.
    ....and that's what I suggested as an alternative possibility. That it continued to be beneficial and the maintenance of the trait wasn't solely due to developmental constraints. If forward facing eyes become no more advantageous or disadvantageous than sideways facing eyes, then yes developmental constraint would be the only reason we maintained stereoscopic vision. But if it in fact became a severe detriment compared to sideways facing eyes, a reversion could have occurred.

    There will never be major changes to a winning design. Or at least the most crucial aspects of the winning design. Due to developmental constraints and adaptive aspects.
    Yes, adaptive aspects. If the environment changed to the point where this "winning" design is in fact a hugely losing design, changes will occur - or the lineage will go extinct, whichever happens first.

    That's why all rodents still have a diastema and two upper and two lower continuously growing incisors that sharpen themselves.

    You might start speculating on whether it would be nicer for rodents to have premolars under certain conditions, but they don't come back because we think it would be cool.
    Again, I don't think anyone is trying to say anything of the sort.

    In fact when people think like that, they don't understand evolution at all, or at least don't get the most important aspect of evolution. It is a historic process that is governed by developmental constraints.

    and that is all there is to it.
    What about those adaptive aspects you just mentioned earlier? Look, no one is saying developmental constraints aren't important and I'm pretty sure they played no small role in the maintenance of stereoscopic vision in primates, but to say "This is the only reason and there's no other possible alternatives" is pushing it. However, I'm not sure anymore if that's what you were trying to say because you bring up benefits and adaptive aspects in your post.
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    Quote Originally Posted by spuriousmonkey
    Why do we suddenly all have problems with the fucking obvious.
    Because your "explanation" is so fucking obvious that it doesn't convey any information. Answering a question like "Why do we have binocular vision" with "because as some point out ancestors developed it and it proved useful" is just restating that we evolved binocular vision. Why was binocular vision so useful to our ancestors? Why was it selected for? Was is because it helped with hunting? Was it because it helped with navigating tree branches? Some third reason, or combination of reasons?
    In fact when people think like that, they don't understand evolution at all, or at least don't get the most important aspect of evolution.
    I have not observed anyone in this thread to be thinking like that.
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    still, that may well be the only reason that makes sense : stereoscopic vision developed in our ancestors because it was advantageous - we haven't lost it since then because there was no major selection drive to make us lose it (in other words, it was not more adaptive to go back to all-round vision than to stick with what we inherited)
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  38. #37  
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    Quote Originally Posted by spuriousmonkey
    There will never be major changes to a winning design. Or at least the most crucial aspects of the winning design. Due to developmental constraints and adaptive aspects.

    That's why all rodents still have a diastema and two upper and two lower continuously growing incisors that sharpen themselves.
    If I were a creationist I could sure as hell use this to demonstrate that you are arguing for microevolution and against macroevolution.

    Sometime spurious you just get it into your head to talk crap.
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    on the other hand, spurious does have a point that certain evolutionary steps just don't happen because of developmental constraints
    remember, a chicken still has the capability of growing teeth, it's just that under normal conditions the trigger to make them grow is no longer available
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    There is a difference between constraints and prohibitions. Spurious, in his recent posting, has adopted an absolutist stance that is both wrong, misleading and out of character. From this I deduce he has had too much Merlot, or possibly underestimated the impact of a Gevrey Chambertin.
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    i doubt whether spurious has the funds to afford Gevrey Chambertin - after all, he's only a mere rodent killer
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  42. #41  
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    Quote Originally Posted by marnixR
    i doubt whether spurious has the funds to afford Gevrey Chambertin - after all, he's only a mere rodent killer
    Precisely my thinking. So he would be unprepared for its subtle assault had he chanced to intercept a bottle en route to the top table at dinner function. (I think we can all see spurious intecepting wine bottles using his stereoscpoic vision to hone in on the target.)
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    I think that predators have eyes which predominatly face forwards for clear vision of prey. However, herbevors and prey have eyes on the sides see they get an almost 360 degree vision from which to look out for predators.



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    Any understanding of human physical evolution needs to keep into account that we are a social species... and that we have complex methods of sharing information.

    As a complex social animal we have pooled our offenses and defenses. The is no need for 'an' individual to be all things at all times. Like gorillas and chimps we moved in groups and like these apes we shared vigilance of danger around us. This lessened the need for each individual to have a broader range of vision...the group as a whole combines their vision (and hearing). The advantages of Stereoscopic vision is feasible for each individual without losing the full advantage of individual broader vision....the group is the principal dynamic.

    An aside: I'm an invertebrate paleontologist and one of the advantages is that nobody gets their knickers in a knot over speculation about brachiopods, echinodermata, etc. .....drift over into vertebrates and debate takes on a much more subjective tone.
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    The advantages of Stereoscopic vision is feasible for each individual without losing the full advantage of individual broader vision....the group is the principal dynamic.
    Not to mention that we can easily look around without needing to turn the whole body. Forward facing eyes means the ability to judge distance better, so better jumping around in trees, better hunting, etc., plus the added benefit of being able to devote the entire visual cortex to an object of interest.

    drift over into vertebrates and debate takes on a much more subjective tone.
    Probably because we have less to identify with when it comes to invertebrates.
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    Quote Originally Posted by raptordigits
    Any understanding of human physical evolution needs to keep into account that we are a social species... and that we have complex methods of sharing information.

    As a complex social animal we have pooled our offenses and defenses. The is no need for 'an' individual to be all things at all times. Like gorillas and chimps we moved in groups and like these apes we shared vigilance of danger around us. This lessened the need for each individual to have a broader range of vision...the group as a whole combines their vision (and hearing). The advantages of Stereoscopic vision is feasible for each individual without losing the full advantage of individual broader vision....the group is the principal dynamic.
    Perhaps true, but chimpanzees spend large amounts of time in small groups or even alone, especially females. They live in the bounds of a single territory but often go their own ways within that territory, far from other individuals. Modern day chimpanzees also have no known habitual predators besides each other, most likely due to their large body size. And gorillas definitely have no known habitual predators. Grouping for the purposes of predator defense probably hasn't been relevant to great apes for quite some time.

    An aside: I'm an invertebrate paleontologist and one of the advantages is that nobody gets their knickers in a knot over speculation about brachiopods, echinodermata, etc. .....drift over into vertebrates and debate takes on a much more subjective tone.
    Scientists are people, and like any other group of people, someone is going to get their knickers in a knot about something at some point. I kind of doubt that the field of invertebrate study is a complete exception.
    Man can will nothing unless he has first understood that he must count on no one but himself; that he is alone, abandoned on earth in the midst of his infinite responsibilities, without help, with no other aim than the one he sets himself, with no other destiny than the one he forges for himself on this earth.
    ~Jean-Paul Sartre
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    WYSIWYG Moderator marnixR's Avatar
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    i suppose there are no examples of stereoscopic vision amongst invertebrates (at least amongst the ones that have eyes) ?
    "Reality is that which, when you stop believing in it, doesn't go away." (Philip K. Dick)
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    Forum Radioactive Isotope Paleoichneum's Avatar
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    Quote Originally Posted by marnixR
    i suppose there are no examples of stereoscopic vision amongst invertebrates (at least amongst the ones that have eyes) ?
    Pacopid Trilobites and Salticid (jumping) spiders
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    WYSIWYG Moderator marnixR's Avatar
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    are you sure about phacopids ?



    doesn't look particularly stereoscopic to me ...
    "Reality is that which, when you stop believing in it, doesn't go away." (Philip K. Dick)
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    Forum Radioactive Isotope Paleoichneum's Avatar
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    Quote Originally Posted by marnixR
    are you sure about phacopids ?



    doesn't look particularly stereoscopic to me ...
    Yes I am sure. however I shouldn't have been lazy and should have reinvestigated beyond my memory more.

    Phacopids had schizochroal eyes. in other words compound eyes with large lenses and less lenses then other compound eyes. Each lens had its own cornea and was a doublet, eg two separate lenses aligned to reduce birefringence from the calcite forming the lens.

    Combine these factors and you end up with an order of animals with stereoscopic vision in each eye separately.
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