As I get older I began to think the opposite; that our thoughts, personalities, and everything original about us are a product of our physical composition and brain structure.
I began to really notice this after reading Principles where Ray Dalio observes that the way people think and approach and solve problems are largely fixed. I notice this in myself and the people around me.
There was a sort of inflection point for me after getting my first massage. My body was completely relaxed, resulting in my mind being completely relaxed. After the massage I went to a trader joes in columbia maryland during a saturday. This trader joes is a logistic nightmare that always stresses me out, so much so that I would usually avoid going during peak shopping. But this time I was completely unbothered, nothing about the experience was bothering, my thoughts were completely at ease. At that moment I realized that it wasn't stress making me tight, it was tightness making me stressed. The dependency was completely backwards from the way I thought. Being self centered i thought my thoughts informing my physical, but it was actually my physical causing my thoughts.
I have genetically high blood pressure, and I have to consume low sodium in order to keep it under control. While I was learning this and my blood pressure was high, I was literally angry about everything. Road rage, meltdowns at home, being short and explosive with my wife and son. I thought it was stress or affect from work I thought it was thoughts/personality -> body. As soon as I experimented with reducing sodium, getting exercise and my blood pressure dropped, my mood completely rounded out and fixed itself. IT was actually my body -> thoughts.
The same thing happens with hiking spending time outside. I used to feel like a connected, or spiritual relationship with the outdoors. I enjoyed drinking and camping, I thought that there was a spiritual relationship with the outdoors (personality -> body) when, once again, it's actually just physical -> personality, dopamine is released, my blood pressure probably dropped my thoughts became more relaxed, my body was tired and relaxed from hiking.
I think that we really are a lot less conscious than we think we are, and that the way we think, our personalities, and pretty much everything about us is largely predetermined by our physical composition. I think we're just more complicated animals and our personalities are just a response to physical input and reactions.