As man is at the present time, he has no influence at all upon his physical body. What man physically is and does is brought about from outside by creative forces. He cannot himself regulate the movement of the molecules of his brain; neither of himself can he control the circulation of the blood. In other words, the physical body is produced independently of man and is also sustained for him by other forces. It is as it were only lent to him. Man is incarnated into a physical body produced for him by other forces.
Source: Rudolf Steiner – GA 93a – Foundations of Esotericism – Lecture II – Berlin, 27th September 1905