According to Descartes, the soul and the body meet in the pineal gland. In this fashion, Descartes was able to incorporate the church's view into his theory. However, there is another problem. In fact, all mammals have pineal glands. Today this is not a problem because modern sciences employ a different perspective, namely that humans are animals.
All animals show variations and options of behavior.
Pet owners will observe how their pets will do different things on different days. There is a belief that we can account for human and animal behaviors on purely physical basis. Scientifically nothing follows from, is predicted by, or is falsifiable on the basis of postulating a soul. However, this notion does not exclude a belief in God or that one cannot believe in a god or gods. The assertion is that we cannot explain behavior on the basis of religious belief.