The human body is simply one variety or model that YOU, the owner of your body function in this reality through. It's a little like owning a car and driving it. YOU are not your car, you simply drive your car and you have a variety of models and brands to choose from when you are in a position to upgrade. I suggest that it may be the same with our bodies, when they have served their purpose we discard them for a different and hopefully, upgraded model!

You asked for theories - this is just mine and MHO!