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The human body is amazing. But there seems to be some evolutionary changes that appear to not make sense regarding redundancy.

While not necessarily the primary reason for their existence, the human body has a great deal of redundancy.

  • Two eyes.

  • Two arms.

  • Two legs
  • Two ears
  • Two nostrils
  • Two lungs
  • Two kidneys
  • Two sets of teeth
  • A very large liver that can work in part.
  • Two brain hemispheres that can (to some degree) do the work of the other.
  • An appendix that is not critical.

But why do we not have two hearts? It would seem like a good idea to have two smaller hearts, together they work above optimally, but survival would be possible with one.

James
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Paul Spain
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  • Having two of almost all of those body parts is absolutely better than one i.e there is no redundancy. Even if a smaller liver can sustain a human, a bigger one is more tolerant to potentially harmful toxins. The brain can reassign parts of the brain to an incredible degree after a hemispherectomy, but not completely depending on age and type of trauma. It also looks like our appendixes are important for our digestion system too. – James Oct 13 '15 at 05:15
  • Two atria and Two ventricles.... – AMR Oct 13 '15 at 06:37
  • One esophagus, one trachea, one stomach, one spleen, one thymus, one small intestine, one large intestine, one thyroid, one spinal cord, one diaphragm, one penis (apologies to those with Diphalia), one tongue, one vagina, one clitoris, one cervix, one uterus, one urethra, one umbilicus, one rectum, one anus... what's your point? – AMR Oct 13 '15 at 06:56
  • @AMR If you're referring to my comment re: two is better, I should have prefaced it with the ancestral symmetry answer. This question is flawed in my opinion because it assumes symetrical anatomy has absolute redundancy. These symmetrical body parts work together to perform optimally with their partner and are not redundant. The question requires a fairly speculative answer based on false assumptions that we may never be able to scientifically test. – James Oct 13 '15 at 09:44
  • @GoodGravy oh heaven's no... I was not commenting about your comment... It was an observation about the question... – AMR Oct 13 '15 at 17:25
  • @AMR I see now! Still, I should have given my first comment more context. – James Oct 13 '15 at 19:40
  • OP. How would you coordinate two pumps in order to maintain proper fluid pressure? Or get them to respond in unison to fight or flight hormones? Imbalances would likely create eddies in the blood vessels that could lead to air embolisms or clots. Even for normal function, you would need the timing to be exactly correct. How would you propagate that impulse between the separated organs? All of the examples of duplicates are capable of working independently, though, as @GoodGravy said to perform optimally, they work together. The two hearts would need to work together perfectly to work at all. – AMR Oct 14 '15 at 00:09
  • @AMR there are other animals that have more then one heart. Worms for example have 5 hearts. I agree a worm is simple in comparison but it has obviously found a way to work with more than one heart. – Paul Spain Oct 14 '15 at 21:26
  • @AMR also while we do have 1 of lots of other things there is normally a very good reason why there is only 1. Such as the space needed to have it, or the energy required to keep it working. In the case of a heart it would be possible to have two smaller hearts and maintain a fully working system that could cope with some damage. Also two smaller hearts may work better as they don't need to be as powerful as they are only pumping blood "halfway" around. – Paul Spain Oct 14 '15 at 21:30
  • Two arms working together is clearly better, And is probably the reason we have two. But four would be even better! but we don't have four. We don't have four as it would be too bulky and too expensive to maintain. Thats a good answer for arms. But that douse not explain a single heart. – Paul Spain Oct 14 '15 at 21:33
  • And clearly one heart is good as that's why we have one heart. But there must have been a good reason to stick with one and not develop two. The point is not to say evolution is wrong. its to answer why it chose what it chose. – Paul Spain Oct 14 '15 at 21:35

1 Answers1

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It is not about redundancy. There are evolutionary and developmental reasons why we have two eyes or two legs and one heart. However just to give you short examples, two eyes are better than one because of our binocular vision while we have two legs because of its locomotor energetics.

Dexter
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