descend from higher planets to this planet sometimes fall down to the ground in raindrops. Then they become grass and gradually evolve to higher forms of life.
Dr. Singh.  Oh, that is terrible.
Śrīla Prabhupāda.  These are the workings of subtle energy. What do the scientists know about this? Actually, their knowledge is carried away by  māyā , illusion, and they are thinking, "Oh, I am a very learned scholar."
Soul Transplants?
Dr. Singh.  Śrīla Prabhupāda, what about heart transplants? We know that the spirit soul is within the heart. But nowadays doctors can replace an old heart with a new one. What happens to the spirit soul in each heart? Does the person who receives a new heart also get a new personality?
Śrīla Prabhupāda. No...
Dr. Singh.  Why not??
Śrīla Prabhupāda.  Suppose I get up from one chair and go sit in another chair. Does my personality change? I may change my seat, but does that mean I have changed?
Dr. Singh.  But the heart is changed, and the heart contains the spirit soul.
Śrīla Prabhupāda.  The  Vedas  describe the heart as a sitting place for the soul. So when they transplant hearts, they simply change the soul's seat. The same soul remains. If they could prove that by changing the heart they have increased the patient's duration of life, then that would prove they've caught the spirit soul. But they cannot increase the duration of life, because people have acquired their bodies by a superior arrangement. You have this body, and you must live within it for a certain period. If you simply change one of the parts of your body, that will not help you prolong your life. That is impossible. The doctors think that by changing the heart they will increase the duration of life, but that is not possible.
Dr. Singh.  So a heart transplant is a kind of artificial transmigration of the soul from an old heart to a new one?
Śrīla Prabhupāda . Yes, it is something like that. Kṛṣṇa explains in the  Bhagavad-gītā  (2.13):
dehino 'smin yathā dehe kaumāraṁ yauvanaṁ jarā tathā dehāntara-prāptir dhīras tatra na muhyati
"As the embodied soul continually passes, in this body, from boyhood to youth to old age, the soul similarly passes into another body at death. The self-realized soul is not bewildered by such a change." Changing hearts is just a change of material bodily organs. The heart is not the real source of life, and therefore changing the heart does not prolong the duration of life.
Dr. Singh.  Yes, most heart transplant patients live only a very short time after the operation. But is it ever possible to transplant the soul from one body to another?
Śrīla Prabhupāda.  Sometimes certain  yogīs  can do that. They can find a better body and transfer themselves into it.