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CarbonRobot CarbonRobot
wrote...
Posts: 393
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2 years ago
Why are humans symmetrical in some ways but not others? We appear largely symmetrical on the outside, but on the inside we have most of our vital organs on one side. Some organs come in pairs but most don't. One heart makes sense, but one liver and one pancreas? Why not be perfectly symmetrical?
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wrote...
2 years ago
Never thought about this before.

wrote...
Valued Member
Educator
2 years ago
Some organs are symmetrical, while others aren't because nature doesn't strive for symmetry, unless symmetry improves the organisms survival and reproductive success. Symmetry works well for things like eyes (depth perception, field of view, etc.), ears (identifying the directions of sounds), and limbs (motion by legs/feet work well in even pairs). Internally it's a different story for mammals.

Externally human's are only symmetrical in one plane. Some animals are more symmetric (like a jellyfish) and others much less symmetric (like a fiddler crab).



For reference:

Symmetrical ones are: thyroid gland, thymus, adrenal gland, testis, nasal cavity, bladder, lymph nodes, spinal cord, small intestine, pharynx, larynx, and rectum.

Asymmetrical ones are: pineal gland, pituitary gland, heart, spleen, pancreas, gall bladder, nerves, large intestines.
CarbonRobot Author
wrote...
2 years ago
Interesting, but wouldn't two half livers be a safer bet for someone that gets attacked a lot? Lol.
wrote...
Valued Member
Educator
2 years ago
How would that make a difference? Grinning Face with Smiling Eyes If you're under attack, you're vulnerable regardless of how many livers you have. But on a side note, our liver is already divided into two large sections called the left and right lobe.
CarbonRobot Author
wrote...
2 years ago
Well one mini liver on each side dividing the work. We may protect largely our dominant side so our other liver stays safe. And if one becomes damaged it may give time for regeneration while the other handles more. It isn't certain death is what I'm saying.
wrote...
Valued Member
Educator
2 years ago
From an evolutionary anthropologists viewpoint, we have two lungs, two eyes, two kidneys, etc. because these dual organs gave our ancestor organisms some kind of advantage. For example, we can survive with a single eye for sight, or a single kidney for blood filtration, but two eyes offer the advantage of depth perception, and two kidneys offer the advantage of improving renal function over a long period of time (in fact, a study in the journal Nephrology, Dialysis, Transplantation looked at how people did after getting a kidney removed. The study showed that after 24 years, a decline in renal function occurs in those with a single kidney).

Back to your hypothesis, I cannot comment as to whether having two livers positioned bilaterally will improve survival, since I couldn't find any real-life biological models to compare to. However, do consider that in the event we had evolved with two livers, our circulatory system would have to be designed from the ground-up. Perhaps rerouting everything would mean that our body would use and require more energy, since we'd now need two gallbladders, and more bile production. In turn, two gallbladders would leading to a higher likelihood of health-related conditions involving the liver, such as the formation of gallstones and the obstruction of that pathway, leading to imminent death. Remember, the surgeries we have now didn't exist 100 years ago, so something like the presence of gallstones would lead to complications like, inflammation, and the blockage of bile and pancreatic ducts, without ailment.
CarbonRobot Author
wrote...
2 years ago
I see.
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