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About the eyes I know that it requires for gauging distance as in Modern 3D cameras have two sensors. And two ears for sound source localization using differences in levels and timing (But not yet two microphones in mobile phones/other devices). What about other organs? Even not all organs are in pair. If it is about about redundancy then why not more than two? Thanks for your answer.

ruben
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This isn't a physics question.

Bilateral symmetry in organisms is (probably) an accident of evolution dating back 500 million years or so. Humans are just one example of a very large number of bilaterally symmetric species. There's obviously an evolutionary advantage to bilateral symmetry, but there are still billions of jellyfish, starfish, sea urchins, etc out there so bilateral symmetry isn't the only route to evolutionary success.

John Rennie
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  • I am also confused, not sure where to ask this question.. I mean homo sapiens are sophisticated creature. So Bilateral Symmetry must have some structural benefits over other structure. Is it possible to more mathematically / efficiently create a structure over Bilateral Symmetry.. – ruben May 24 '12 at 13:12
  • Planarian worms (http://en.wikipedia.org/wiki/Planarian) have bilateral symmetry as well. There are probably even simpler animals wth bilateral symmetry but my knowledge of biology doesn't extend that far. I would try to explain why planarians have bilateral symmetry before starting on humans. See http://en.wikipedia.org/wiki/Bilateria for some background info. – John Rennie May 24 '12 at 14:14
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    If you are a worm crawling along the seabed, the front is different to the back, food is ahead of you so put your mouth sense organs at the front end and put waste out of the back end. Below you is seabed and above you is danger so you make your top and bottom different. But there is no difference between left and right, neither side of you is more likely to need protection, or have more food/oxygen/shelter than the other - so no need for any different body parts. – Martin Beckett May 24 '12 at 16:02
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    John, I heartily agree that it is not a physics questions. The thing that is bugging me is, why did you reward it with a answer instead of voting to close? – dmckee --- ex-moderator kitten May 24 '12 at 17:28
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    @dmckee: although it's biology not physics, it's an annoyingly good question. There are lots of ideas about the origin of bilateral symmetry but since we can't reproduce the experiment no-one will ever know for sure how and why it developed. Could we consider it as an example of symmetry breaking? Martin has even provided a mechanism :-) – John Rennie May 24 '12 at 19:31
  • There should be a way to transfer questions to appropriate forum rather than closing :( – ruben May 25 '12 at 06:33
  • Try http://biology.stackexchange.com/ – John Rennie May 25 '12 at 06:34
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    @newcomer: in fact I asked the moderators of [biology.SE] to let me know if they thought this question would be suitable for their site, and if they had, I would have migrated it there. But they didn't. – David Z May 25 '12 at 17:25