4 ms·

Well, our brains are asymmetrical in terms of function, and our bodies are asymmetrical internally too (heart, liver). So, which came first? Are we mostly righ

Well, our brains are asymmetrical in terms of function, and our bodies are asymmetrical internally too (heart, liver). So, which came first? Are we mostly right handed because of left brain functionality (each side of brain controls opposite side of body), or is handedness innate in some other way and perhaps influences brain sidedness? Or, are these two things unrelated?

matteocantiello 2y ago
The findings in chimpanzees indicate that both humans and chimpanzees exhibit population-level asymmetries in handedness, though humans show more pronounced lateralization (e.g. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3676728 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3676728). I think this suggests that anatomical asymmetries in the brain likely preceded handedness and contributed to the evolution of hemispheric specialization. As brain size increased and corpus callosum connectivity decreased, specialized functions in each hemisphere became more pronounced. Thus, handedness and brain asymmetry likely co-evolved, influenced by both genetic and environmental (including socio-cultural) factors, rather than one directly causing the other.
emporas 2y ago
With so many poisonous plants reptiles and insects, it is better to use the hand further away from the heart. In case it gets stinged or bitten or pricked the poison will affect a slightly more remote area.
- lolc 2y ago
  Thank you, that is the best just-so story I've read in a long while! If the subtext is not apparent: https://en.m.wikipedia.org/wiki/Just-so_story https://en.m.wikipedia.org/wiki/Just-so_story
  - emporas 2y ago
    Even if the distance of the right hand to the heart (on the left) is just 10% more than if it was located on the right side, that small difference for 50 million years might be significant enough for a right hand trait to be established in the population. Any scientist who wants to verify this hypothesis (or the-just-so story) is welcomed, and this explanation might be upgraded to totally valid scientific theory or serve as a warning to the general public about unproven scientific falsehoods.
    - HarHarVeryFunny 2y ago
      We've got veins returning blood to the heart on both sides of our body, and it all has to go via the circulatory system - not as-the-crow-flies from any point directly to the heart. In any case, even if there was (seems not) a few seconds delay in terms of how quickly poison from a snake bite on one side of body vs other got to the heart, that's not going to make any difference to survivability. It seems that developmental asymmetry, resulting in (fairly major) left vs right brain functional differences, is what has lead to left vs right handedness.
      - emporas 2y ago
        I would say that brain asymmetry probably is not the cause of hand and leg asymmetry. It has to do either with venomous [1] plants and animals or with muscle use and fatigue. When the hand is stung or burned it performs a quick centrifugal movement instinctively. Then many mammals can suck some blood out with their mouths. That minimizes the venom in circulation, and some additional time to get to the heart might be less damaging, especially when the venom is not very plentiful like bees, scorpions etc. When the venom is of a big quantity, like big snakes then probably it doesn't make a difference. One other factor is muscle isolation and helping the heart to not get tired from work. Considering that the whole point of gyms is muscle isolation, which is very difficult to achieve normally, a human or monkey cracking nuts or cracking bones for hours, it will tire the left side (where the heart is located) much more increase palpitations, and consequently the risk for heart attack. That last one could be tested, working more using the left hand -> increase palpitations or not. As a counter example, the chimp when it cracks the turtle, it works with both hands [2]. [1] Venomous not poisonous i misspoke previously. [2] https://www.youtube.com/watch?v=o7dRvX2f9Rs https://www.youtube.com/watch?v=o7dRvX2f9Rs

matteocantiello 2y ago

The findings in chimpanzees indicate that both humans and chimpanzees exhibit population-level asymmetries in handedness, though humans show more pronounced lateralization (e.g. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3676728 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3676728). I think this suggests that anatomical asymmetries in the brain likely preceded handedness and contributed to the evolution of hemispheric specialization. As brain size increased and corpus callosum connectivity decreased, specialized functions in each hemisphere became more pronounced. Thus, handedness and brain asymmetry likely co-evolved, influenced by both genetic and environmental (including socio-cultural) factors, rather than one directly causing the other.

emporas 2y ago

With so many poisonous plants reptiles and insects, it is better to use the hand further away from the heart. In case it gets stinged or bitten or pricked the poison will affect a slightly more remote area.

lolc 2y ago
Thank you, that is the best just-so story I've read in a long while! If the subtext is not apparent: https://en.m.wikipedia.org/wiki/Just-so_story https://en.m.wikipedia.org/wiki/Just-so_story
- emporas 2y ago
  Even if the distance of the right hand to the heart (on the left) is just 10% more than if it was located on the right side, that small difference for 50 million years might be significant enough for a right hand trait to be established in the population. Any scientist who wants to verify this hypothesis (or the-just-so story) is welcomed, and this explanation might be upgraded to totally valid scientific theory or serve as a warning to the general public about unproven scientific falsehoods.
  - HarHarVeryFunny 2y ago
    We've got veins returning blood to the heart on both sides of our body, and it all has to go via the circulatory system - not as-the-crow-flies from any point directly to the heart. In any case, even if there was (seems not) a few seconds delay in terms of how quickly poison from a snake bite on one side of body vs other got to the heart, that's not going to make any difference to survivability. It seems that developmental asymmetry, resulting in (fairly major) left vs right brain functional differences, is what has lead to left vs right handedness.
    - emporas 2y ago
      I would say that brain asymmetry probably is not the cause of hand and leg asymmetry. It has to do either with venomous [1] plants and animals or with muscle use and fatigue. When the hand is stung or burned it performs a quick centrifugal movement instinctively. Then many mammals can suck some blood out with their mouths. That minimizes the venom in circulation, and some additional time to get to the heart might be less damaging, especially when the venom is not very plentiful like bees, scorpions etc. When the venom is of a big quantity, like big snakes then probably it doesn't make a difference. One other factor is muscle isolation and helping the heart to not get tired from work. Considering that the whole point of gyms is muscle isolation, which is very difficult to achieve normally, a human or monkey cracking nuts or cracking bones for hours, it will tire the left side (where the heart is located) much more increase palpitations, and consequently the risk for heart attack. That last one could be tested, working more using the left hand -> increase palpitations or not. As a counter example, the chimp when it cracks the turtle, it works with both hands [2]. [1] Venomous not poisonous i misspoke previously. [2] https://www.youtube.com/watch?v=o7dRvX2f9Rs https://www.youtube.com/watch?v=o7dRvX2f9Rs