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 us

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