Heart Left Side - why?

Discussion in 'Biology & Genetics' started by sowhatifit'sdark, Dec 19, 2007.

  1. sowhatifit'sdark Valued Senior Member

    Wouldn't it be better to have the heart in the middle?
    What is the evolutionary advantage of having an asymmetrically placed heart?
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  3. Oniw17 ascetic, sage, diogenes, bum? Valued Senior Member

    Your sternum doesn't seem as flexible. People with gigantism get exhausted easier because the muscle mass around their heart makes it harder to pump blood fast enough, so the fact that your ribs are super flexible may have something to do with it. That's just a guess though. Also, some peopl are born with their heart on the right side I believe.
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  5. Orleander OH JOY!!!! Valued Senior Member


    My Mom was.

    Please Register or Log in to view the hidden image!

    She was born with a multitude of problems, and that was the only one that didn't affect her.
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  7. Read-Only Valued Senior Member

    Who says it would be an advantage? Wouldn't having at least one eye in the back of our heads also be an advantage over those who don't have one???
  8. I-Am-Invisible sick of it all. Registered Senior Member

    the bloodstrem has two "cycles", one: heart - lung - heart and then following heart - the body - heart. the second part is much larger and it requires more strength to get the blood circulating, since the whole body needs to be supplied. the left side of the heart is responsible for this, while the right side only needs to pump the blood to the lung and back. since the two different chamers have different requirements in terms of strength, they are built differently and therefor asymetrical...

    the condition where the heart is leaning to the right side is situs inversus... all organs are mirrored

    Edit: the evolutionary advantage ist we get better blood supply because the heart is optimized for the pumping capacity needed and therefor we perfom better at tasks that are physicaly demanding.
  9. sowhatifit'sdark Valued Senior Member

    It was a question.
    I notice that there is a tendency towards symmetry. It seems like this was valued.
    The heart is distributing blood to the body, from a central position this might be more balanced.
    I don't know.
  10. sowhatifit'sdark Valued Senior Member

    Thanks. This seems to be heading towards the answer for me.
    I understand how the above makes the heart itself asymmetrical, but still not why the whole heart is shifted to the left.
  11. sowhatifit'sdark Valued Senior Member

    Oh, yes. Is the heart on the left in other species, especially mammals?
  12. Orleander OH JOY!!!! Valued Senior Member

    and aren't there mirror image identical twins? If so, wouldn't the heart be on the wrong side of one of them?
  13. SkinWalker Archaeology / Anthropology Moderator

    The heart is, itself, symmetrical, but its an individual organ rather than one that comes in a pair (like kidneys, eyes, testicles, etc). As such it has to occupy the space in the chest cavity somewhere -so why not slightly to the owner's left? Slightly to the right are liver and gall bladder, also individual organs, though not quite as large as the heart.

    Overall, the heart is well located. It may be that there's an evolutionary advantage to having it slightly to the left since most humans are right-side dominant and this might afford a bit more protection since the right side may have been first to encounter dangerous circumstances. But I'm completely speculating off-the-cuff and have nothing to base that on.
  14. greenberg until the end of the world Registered Senior Member

    The chest cavity is full of things - there are the trachea, big blood vessels, the esophagus. To have the heart squeezed centrally between all these things would likely be a disadvantage.
  15. sowhatifit'sdark Valued Senior Member

    Sounds possible.
    I just found this, said by some guy - so I make no claims to his authority, on the internet.

    In mammals, the aorta (the major artery carrying blood to the body) bends to the specimen's left side. In birds and reptiles, the aorta bends to the specimenĀ¹s right side. This alteration reflects a difference in the evolution of these two types of vertebrates from a common, more fish-like ancestor. That is the difference you are wondering about.


    Generally, the heart of vertebrates lies in the approximate center of the thoracic (chest) cavity. For fish this is generally perfect because the pattern of circulation is symmetrical about the heart (the gills are exactly the same on both sides). In other vertebrates in which the primitive (reflected in the early embryo) pattern is reorganized to accommodate the lungs, the altered pattern of major vessels tends to give the appearance of the heart being set to the right or left in the thorax (chest cavity).
  16. sowhatifit'sdark Valued Senior Member

    This article does not directly address my question but is nevertheless fascinating:


    How your heart got where it is:
    Electricity shapes your body


    It is focusing on how we end up being asymmetrical and (not so)recent indications that small electric fields may cause this. I found the last section most interesting about the regeneration of body parts.
  17. MikeB Registered Member

    Isn't the liver bigger than the heart?
  18. MikeB Registered Member

  19. origin In a democracy you deserve the leaders you elect. Valued Senior Member

    Welcome and thanks so much for asking those 2 questions - I have been patiently waiting at my computer for 7 1/2 years for those exact questions.

    The answer is yes and kinda.

    Finally, I can get up from this chair, my back is killing me!
  20. Magical Realist Valued Senior Member

    Ancient soldiers would fight with their right-hand clenched swords while holding a shield with their left. Over time the soldiers with hearts further to the left tended to survive battle more because it was more easily protected by the shield, thus passing their genes for "heart leftness" to future generations.

    On second thought, nix that. Evidently the heart isn't really left enough for this to have played any role at all. But ya gotta admit, it sounded good!
    Last edited: Jun 26, 2014
  21. Fraggle Rocker Staff Member

    The eye itself and the bundle of nerves that service it take up a lot of space. This would either result in a smaller brain, or require the cranium to be larger, which would make us even more top-heavy. And speaking of the brain, yet another enormous portion of it would need to be dedicated to the third eye: focusing, blinking and correlating its images with those of the other eyes.

    Evolution stopped with two eyes because that gives animals depth perception, and that seems to be good enough. Fish, the first chordates, evolved in a three-dimensional environment, and even they seem to be okay with just two eyes. And so are the more recently evolved denizens of a 3-D milieu: birds.

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