Thank you Joachim

Thanks for those responses.

Next question- why is your sense of smell NOT cross-wired?

I assume it is because the ability to detect chemicals in the immediate environment evolved long before vertebrates did, but have never seen an attempt to explain this oddity.

Any thoughts?

Paul.

very interesting question. The fact that olfaction is different to the other sensory systems is just another index for its separate and outstanding function. That of course explains nothing. An additional helpful thought might be that we should not think in terms of purpuses, which is why the why question at least sometimes might be answered with "due to random happenings". Things happen in evolution and if they are not hindering they survive.

These are just some quick and dirty ideas before going to bed.

Thanks

Hi Peter,

Quick and dirty ideas before going to bed are the best!

Auditory coding is not all cross-wired, yet when a tree falls in the forest, you can tell which direction the sound came from, (as long as your brain and both your ears are working okay... ...although, sadly, I'm not too sure what happens if you are not there to hear it... ).

http://www.ncbi.nlm.nih.gov/pubmed/2352043

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Our sense of smell is also bilateral, (although, like our hearing, not as impressively "directional" as that of a feline or canid).

http://www.ncbi.nlm.nih.gov/pubmed/2493388?dopt=Abstract

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http://chemse.oxfordjournals.org/content/34/2/139.full

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I'm wondering if either;

cross-wiring is unnecessary for doing something relatively "slow", like determining the direction of a smell, but facilitates the sort of topographic information processing needed to judge distances and velocities and guide rapid intuitive movement, (fly to that flower, leap out of the reach of that mantis, whip out your tongue to catch a fly, pounce on a mouse, head-butt the other male Bighorn, run across the loose stones to escape the hawk, jump and swing to another branch, accurately throw a stone or stick to hit a target, perform an "eskimo roll" in a kayak), and so having visual and motor systemns wired this way is adaptive?

Or;

maybe our brain wiring is (as you suggest) largely an accidental product of our history, just like the keyboard you are typing with.

The "qwerty" keyboard layout was designed in the 19th Century, when type-writers were very prone to jamming. The "qwerty" layout places the most commonly used keys evenly spaced across the board. In old fashioned machines, this meant the individual bar which struck the page was less likely to jam against it's neighbours. Placing commonly used letters widely apart slows typing speeds down, which also reduced jamming on old fashioned machines.

Of course modern, electronic keyboards don't have these mechanical problems. There are several designs for more efficient keyboard layouts that dramatically increase typing speeds. The reason we haven't ever adopted these more rational keyboards, is that it would cost too much to replace all that hardware and software and retrain all those people.

It may be that our noses and ears evolved from organs for sensing chemicals in the nearby environment (smell) and sensing vibrations (hearing) that were present in organisms that predated primitive chordates; that our cross-wired other senses evolved amongst earlier chordata and early vertebrates, for reasons like the ones Joachim has already suggested; and that the layout persists in birds, reptiles and mammals even though it is no longer necessary simply because (like the foundations of a very large, very old house) they are buried so deeply and intimately in everything that has been evolved since that it would be too costly to change them.

If human or primate brains needed cross bi-laterality to process complex sensory information, then how come they can adapt to glasses with lenses that invert the up/down and left/right transposition?

http://www.cns.nyu.edu/~nava/courses/psych_and_brain/pdfs/Stratton_1896.pdf

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http://www.sciencedirect.com/science/article/pii/S0928425704000816

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I have no evidence, but I suspect a crow, rat, cat. or dog would adapt to such glasses just as efficiently as primates do. In fact I suspect a frog would get used to these lenses as well. (Not too sure about the bees, though). The only reason we have evolved such complex and responsive nervous systemns is to be able to learn from, and adapt to, changing environments.

So, any ideas for how we could tell whether cross-wiring is advantageous, or just a relic piece of evolutionary noise that slightly slows our reaction time but is too deeply buried to mess with? Does anyone know of any published literature that might inform this sort of question?

Paul

There is a related conversation here;

https://www.researchgate.net/post/What_is_the_scientific_explanation_for_the_left_part_of_brain_controlling_right_part_of_body_and_vice-versa?ev=home_person_like_comment_question_target

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Paul.

After a few readings, it seems that there is not one answer to this question but a lot of answers !

Especially there are theories for human beings (adaptation or evolution) for motor cross wires, explanations for uncomplete cross wires for hearing and sense of smell and optic chiasma is there for necessity to rebuilt images and helping stereoscopic vision. But for the moment I have not seen an explanation for skin and articular sensibility crossing

Some help ?

Because evolutionary system, from the littlest to the bigger implications. The nervious system evolved since the beginning of the living.

http://www.ncbi.nlm.nih.gov/pubmed/23447666

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So an eye that is wired directly into the spinal column is good enough to allow an organism to move towards or away from visual stimuli.

This is probably analogous to moving towards or away from a scent.

But is such an eye good enough to accurately throw or catch a baseball?

Not making an assertion either way, but very interested to see any responses/interpretations/further evidence.

Paul.