1) Why 2 feet [functional to interact w. world] - so, spiritually you can say one leg is inside while the other is in touch with the world. Functionally, it's just how locomotion works: 1 step stable, 1 step to future.
2) Two hands as human advancement over 4 leggers (humans need hands to do more adv. stuff)
3) Eyes - greater depth perception
4) Ears - again greater echolocation
5) 1 Brain/1 heart/1 Bladder/1 spine.
*1 vs 2 can be explained in their fundamental empiricality.
The key is the focus of the concept. A) Mental thoughts is a singular/directed path and does not require duality. B) There's only 1 trachea/penis (leading to/from 2 lungs/kidneys) because of the fluidity of the "gases/liquids". The functional is 1 direction/but the fluidity allows for the organs to play well with the symmetric nature of the human legs (for human motion).
C) so why is the stomach/colon only 1? Because food is generally solid and it's lack of "fluidity" causes imbalance in the symmetrically system of the legs. Imagine if the burger is lopsided to your left-side; you would be walking in circles. I understand you can say the same about 1 bladder but you can view a body of urine NOT as fluid of air coming in and out of you lungs (over the 3rd dimension of time). So, if you were sleeping on your side, if you had 2 bladders, 1 may fill up and then when u walk, you would walk in circles. But with air, like it's in and out in 2 seconds.
So, nothing is more pure than thought (so only 1 brain is needed), when u interact with the world you need 2 (2 eyes/ears/hands/legs), fluidity interjects in the uni-directional nature of our involvement with air/water and branches out from 1 trachea to 2 lungs. And we take a step back with the complexity of solids within our bodies to just 1 digestive tract.
Please feel free to elaborate (or place another perspective) on the subject. I'm still at my infancy of this idea.