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elbanditoroso's avatar

Are humans designed to be symmetrical?

Asked by elbanditoroso (22018points) 2 months ago

We all have two of a lot of body parts. But it seems like while we things are generally symmetrical, there are lots of flaws and imperfections.

- Eyes. I have known several people with a left eye of one color and a right eye of another color

- Arms (and to a lesser extent legs) where one arm is ¾ to an inch shorter than the other

- Feet: most people have feet of slightly different sizes; no more than a ¼ inch (or one size) different, but they’re not the same

- Breasts. Possibly most visible. Different sizes, different placement on the chest, one points more out, the other more straight ahead.

- Ears. Some people have one a little higher or lower, or front or back, than the other

There are probably more examples, but these are what come to mind.

And I am not even talking about internal organs, such as lungs and kidneys.

Why would evolution, otherwise so effective, have resulted in these odd asymmetricities?

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21 Answers

ARE_you_kidding_me's avatar

Perhaps not designed but evolved symmetry. Humans have bilateral symmetry as opposed to things like starfish that have radial. I suppose the answer has to do with what the starting point was in addition to the obvious advantages. Without symmetry how would protozoa or fish swim properly.

ARE_you_kidding_me's avatar

As far as the imperfections, “good enough” is all that really matters in survival. It’s not like we were designed by engineers and cut from a milling machine.

Zissou's avatar

OP: the things you are talking about have to do with the difference between genotype and phenotype. Those parts may be “designed” to be symmetrical, but may not turn out that way due to environmental factors.

Different eye color would be a genetic thing, though.

Some things, like handedness, are asymmetrical by “design”. We are not fiddler crabs, but things like that may be associated with subtle physical asymmetries for all I know.

Espiritus_Corvus's avatar

Not only are we designed, with a few internal exceptions, to be symmetrical, but we are hardwired to measure beauty and health in the symetry of our faces. An asymmetrical face is noted subconciously and represents ideosyncracy—and our instincts interpret ideosyncracies as undesirabel elements for survival. We are hardwired for comformity and symmetry represents that.

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Darth_Algar's avatar

Because evolution is not perfect, or even necessarily graceful. All that matters, from an evolutionary standpoint, is survival.

RedDeerGuy1's avatar

Yes. Redundant organs in case of accident.

LostInParadise's avatar

The similarities are much more striking than the differences. When I press my hands together, the fingers on my two hands line up exactly.

One question that occurs is if there is a separate DNA program for each hand or a single one, with instructions to make one hand the mirror image of the other. If, for each pair of organs, there are a pair of separate programs, then it is easy to imagine how small mutations can result in differences.

Patty_Melt's avatar

Stop staring at me.

squirbel's avatar

This is why beautiful people exist…also known as as perfectly symmetrical people. They tend to match on both sides and just appeal to the eyes of their onlookers.

ragingloli's avatar

No, humans are not designed.
Evolutionarily, symmetry as a basic trait is useful as it enables good controllability of forward motion and change of direction by providing equally effective cobtrol surfaces on either side, and genetically, duplicating and mirroring is exceptionally trivial.

Dutchess_III's avatar

All animals are symmetrical. It worked best from an evolutionary POV.

Zissou's avatar

I’ve heard there is a separate gene for the hair on each segment of each finger.

Welcome back, old-timer

LuckyGuy's avatar

Have you ever taken an mechanical drawing class? It is far easier to make a line or plane of symmetry and then flipping it over to make the other half of an object. It takes far less effort (a little more than half) to encode the information rather than encoding both sides. Symmetry makes locomotion easier.
That said If I were responsible for the design I’d make some serious changes.
1) Reproduction and liquid waste removal are critical functions. They need to have redundant and separate features.
2) Physical prowess no longer applies in the internet age. I’d make the opposite sex be attracted to mind and or wealth rather than physical attributes.
3) I’d allow stem cells to activate and regenerate missing or damaged body parts.
4) I’d modify the number of telomeres to produce a failure at a known date. If expiration dates were known, people could plan accordingly and wisely.

I’ll be thinking of more. I’m an engineer – I can’t help it.

JLeslie's avatar

Symmetry seems to make sense. When we are very out of whack it cause all sorts of problems. One leg much shorter than the other we walk with a limp, it is bad for our spine, it slows us down, and it doesn’t look as attractive.

Our two eyes work together to properly evaluate depth and location of an object, and gives us peripheral vision on both sides.

It seems it’s innate for symmetry to be more appealing. The more symmetrical the higher score people get in the beauty department.

Probably, something with how our cells divide and multiply makes symmetry easier in nature. Just a guess. I’ve always been fascinated that not all of our internal organs are duplicated. We have two ovaries, two kidneys, but only one liver, one stomach, I wonder why.

Pinguidchance's avatar

Are humans designed to be symmetrical?

Organisms with a central nervous system display bilateral symmetry.

Designed? Do you perchance prefer a discussion about the big g spot in the sky?

LuckyGuy's avatar

@Pinguidchance Thanks for reminding me of another improvement:
I’d add a second g spot – and place it on the tip of the tongue.

Darth_Algar's avatar

Why do I get the feeling that some folks didn’t really read the opening post?

Dutchess_III's avatar

To answer this question: Why would evolution, otherwise so effective, have resulted in these odd asymmetricities?

The asymmetric trails6 you listed are not life threatening. They may affect your ability to attract a mate tho.

Jeruba's avatar

Apparently not. There seems to be a lot of leeway, doesn’t there? I’d have to say those variations must not be a problem, from an evolutionary or survival standpoint.

Pinguidchance's avatar

@LuckyGuy that answer was on the tip of my tongue before it rolled off yours.

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