# body symmetricality

**URL:** <https://boards.straightdope.com/t/body-symmetricality/45301>\
**Category:** Factual Questions\
**Created:** [December 13, 2000, 3:42am UTC](https://boards.straightdope.com/t/body-symmetricality/45301 "2000-12-13T03:42:00Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![kryptonite2](https://avatars.discourse-cdn.com/v4/letter/k/85e7bf/32.png) [@kryptonite2](https://boards.straightdope.com/u/kryptonite2)\
**Post date:** [December 13, 2000, 3:42am UTC](https://boards.straightdope.com/t/body-symmetricality/45301/1 "2000-12-13T03:42:00Z")

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why is it that the outside and inside layers or the human body seem to be symmetrical but when it comes to organs, such as the heart, liver etc, they are not arranged symetrically? is there a developmental biology explanation for this?

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**Author:** ![edwino](https://avatars.discourse-cdn.com/v4/letter/e/35a633/32.png) [@edwino](https://boards.straightdope.com/u/edwino)\
**Post date:** [December 13, 2000, 4:41am UTC](https://boards.straightdope.com/t/body-symmetricality/45301/2 "2000-12-13T04:41:01Z")

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A simple explanation is that most of the organs form in the midline and migrate in embryogenesis towards one side. The migration usually occurs with looping and twisting of the tissue, like with the heart and the intestines. Other organs, like the lungs and the liver, branch off of other structures and fill in the “extra room.”  
This rotation depends on several genes, and several disorders (most collectively called situs inversus) affect these genes and organ alignment.

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**Author:** ![KarlGauss](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/karlgauss/32/3713_2.png) [@KarlGauss](https://boards.straightdope.com/u/KarlGauss)\
**Post date:** [December 13, 2000, 4:56am UTC](https://boards.straightdope.com/t/body-symmetricality/45301/3 "2000-12-13T04:56:23Z")

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[This thread](http://boards.straightdope.com/sdmb/showthread.php?threadid=45357), on mirror-reversed organ placement, may be of some tangential interest and relevance to you and your question respectively.

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**Author:** ![greeny2](https://avatars.discourse-cdn.com/v4/letter/g/c5a1d2/32.png) [@greeny2](https://boards.straightdope.com/u/greeny2)\
**Post date:** [December 17, 2000, 6:42am UTC](https://boards.straightdope.com/t/body-symmetricality/45301/4 "2000-12-17T06:42:16Z")

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One of the more fascinating of the organ swaps occurs in the sunfish, where one eye actually starts on one side of the embryo and crosses over during maturation so the fish can swim on one side.

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**Author:** ![wevets](https://avatars.discourse-cdn.com/v4/letter/w/e9a140/32.png) [@wevets](https://boards.straightdope.com/u/wevets)\
**Post date:** [December 17, 2000, 6:08pm UTC](https://boards.straightdope.com/t/body-symmetricality/45301/5 "2000-12-17T18:08:15Z")

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Er… the sunfish?? Such as [this bigear sunfish](http://animaldiversity.ummz.umich.edu/media/fink/lepomis_megalotis.jpg), or the [bluegill sunfish](http://www.dnr.state.mn.us/fish_and_wildlife/fish/bluegill_sunfish.html)? Or maybe the [Ocean sunfish](http://www.earthwindow.com/mola.html)?

I think you meant “flatfish.” Like flounder, halibut, etc. 😉