Symmetry is everywhere in nature, and we usually associate it with beauty: a perfectly shaped leaf, or a butterfly with intricate patterns
mirrored on each wing. But it turns out that asymmetry
is pretty important, too, and more common than you might think, from crabs with one giant pincer claw to snail species whose shells’
always coil in the same direction. Some species of beans only climb up
their trellises clockwise, others, only counterclockwise, and even though the human body
looks pretty symmetrical on the outside, it’s a different story on the inside. Most of your vital organs
are arranged asymmetrically. The heart, stomach, spleen, and pancreas
lie towards the left. The gallbladder and most of your liver
are on the right. Even your lungs are different. The left one has two lobes,
and the right one has three. The two sides of your brain look similar,
but function differently. Making sure this asymmetry is distributed
the right way is critical. If all your internal organs are flipped,
a condition called situs inversus, it’s often harmless. But incomplete reversals can be fatal, especially if the heart is involved. But where does this asymmetry come from, since a brand-new embryo looks identical
on the right and left. One theory focuses
on a small pit on the embryo called a node. The node is lined with tiny hairs
called cilia, while tilt away from the head
and whirl around rapidly, all in the same direction. This synchronized rotation pushes fluid
from the right side of the embryo to the left. On the node’s left-hand rim, other cilia sense this fluid flow and activate specific genes
on the embryo’s left side. These genes direct the cells
to make certain proteins, and in just a few hours, the right and left sides of the embryo
are chemically different. Even though they still look the same, these chemical differences are eventually
translated into asymmetric organs. Asymmetry shows up in the heart first. It begins as a straight tube
along the center of the embryo, but when the embryo
is around three weeks old, the tube starts to bend into a c-shape and rotate towards
the right side of the body. It grows different
structures on each side, eventually turning into the familiar
asymmetric heart. Meanwhile, the other major organs
emerge from a central tube and grow towards their ultimate positions. But some organisms, like pigs,
don’t have those embryonic cilia and still have asymmetric internal organs. Could all cells be
intrinsically asymmetric? Probably. Bacterial colonies grow lacy branches
that all curl in the same direction, and human cells cultured
inside a ring-shaped boundary tend to line up
like the ridges on a cruller. If we zoom in even more, we see that many
of cells’ basic building blocks, like nucleic acids, proteins, and sugars,
are inherently asymmetric. Proteins have complex asymmetric shapes, and those proteins control
which way cells migrate and which way embryonic cilia twirl. These biomolecules
have a property called chirality, which means that a molecule
and its mirror image aren’t identical. Like your right and left hands,
they look the same, but trying to put your right
in your left glove proves they’re not. This asymmetry at the molecular level
is reflected in asymmetric cells, asymmetric embryos, and finally asymmetric organisms. So while symmetry may be beautiful, asymmetry holds an allure of its own, found in its graceful whirls, its organized complexity, and its striking imperfections.

100 thoughts on “Why are human bodies asymmetrical? – Leo Q. Wan”

  1. It is more surprising to realize how we look pretty symmetric on the outside, while pretty much all the building blocks of our body are asymmetric.

  2. My theory is that, while symmetry has its own merits, for example, most animals are "two-sided" because of the necessity of sensing direction and movement; like stereo speakers, ears, nose, eyes gather external information in separate directions to form a cohesive data of the environment. Movement; I'll leave that to biomechanics, but most vertebrae are "two-sided" for movement.
    However, with all these merits from symmetry, vital parts, which are of higher importance like digestive organs simply do not have space or resource to have a pair inside the bodies of animals, and that the function of it is enough to function as a sole part of the body.
    Try imagining trying to fit two engines inside a car. Not only is it unnecessary, but difficult too. I forgot who mentioned this quote but; "Form follows function."

  3. I think it is bcoz that if we got injured on one side we can still have few chances that our vital organs are if u agree

  4. These are perfect for bedtime because they keep me thinking as I drift to sleep what a good way to sleep

  5. So, why are our feet symmetrical, then? You're right glove doesn't fit on your left hand, yet either sock fits on either foot.

  6. This is why traditional architecture in Germany is so beautiful, and interesting, compared to traditional architecture in English speaking countries, which is symmetrical ad nauseum. Asymmetry, and angled lines, are all integral to German design.

  7. Just curious: might any of this have to do with the asymmetry of chiral compounds in the body: of an L- and a D- version?

  8. 0:38 It might look pretty symmetrical at a first glance, but take a picture of one side of your face or body, flip one and overlay them, you will find out just how different they are. We use our facial muscles and our body's organs very differently on each side, resolting in major differences (and of course, some differences we are simply born with).
    It's actually kinda weird when you think about it. Since looking at a reflection shows us an inverted image of ourselves, we actually never see ourselves the way others do (unless we're looking at a flipped picture of ourselves).

  9. Nobody’s outside of there body is symitracal, everyone has one side of their body bigger than the other, sometimes it’s just more noticeable than other people 🙂 so if your insecure about it, don’t worry, love yourself

  10. I came here to get an answer to "Why are human bodies asymmetrical" as in what are the benefits. I didn't want an explanation of how cell orientation.

  11. The more we learn about nature functions the more ridiculous evolution sounds. Now I'm giving religion a pass, I'll take evolution a millions time before religion. We might be the product of an another life form, the same way we create video games. GTA characters would eventually become scientiest and figure out everything in their world in constructed of ones and zeros arranged in different patters – well it's an idea … can't be certain for sure. Evolution could be true – but there could have been an external input revising and correcting the process – once things were good enough …. only one problem …. where would that intelligent life form would come from and how would it come into existence? …aghh we back to square one no matter what. One thing is for certain. System don't improve own their on just because time passes.

  12. Asymetrical ears (height or shape) are not mentionned here, but i believe it's common enough..even if it's not noticeable, it really screws up your glasses? :p
    The dominant hand or leg should be more muscular too, i think.
    Some body parts that come in pairs, obviously, (i m betting you r thinking of one or two ''improper'' parts right now hh) , i'm guessing, their different shapes come from asym' muscular use or the oxygenated blood flow..
    I feel like the quality of my hair isn't the same on the two halves of my head :p guess it has to do with wich side i favor in my sleep :p it's usually the kind of observation i share while poeple look at me like i m a freak

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