My dear Dr. Wolf-Rottkay,
Please accept my blessings. I am in due receipt of your letter dated June 14, 1975 and have noted the contents. Biological evolution is taking place on account of the soul's desire. It takes place because of infection. If a man has smallpox virus, then he is subjected to smallpox. It is not that everyone is infected and everyone is attacked with smallpox disease. Only the person who is infected, he is attacked.
In this connection Krishna says in the Bhagavad-gita, purusah prakrti-stho hi bhunkte prakrti-jan gunan karanam guna sango'sya sad-asad-yoni-janmasu (BG 13.22). Purusa means the living entity, or the soul. He is subjected to be infected by the modes of material nature. There are 3 modes of material nature, sattva-guna, raja-guna, tama-guna. And when they are mixed up, they become 3 x 3 = 9, and 9 x 9 = 81, and in each quality, there are millions of forms. Therefore the total number of forms is 8,400,000.
So, the diseases are there and the forms of disease are also there. Material form means diseased form. Therefore, one has to change this form—death. And he carries with him the infection and he develops another disease. In this way, the soul although part and parcel of God in diseased condition, they are forced to change body. That is transmigration of the soul from one body to another.
To be more clear, the disease is there. Just as the Small-pox disease is there. One has to become diseased, being infected. Similarly, the forms of the body are there. One has to infect the form and it develops. karanam guna sango'sya sad-asad-yoni-janmasu. Because he is infecting different diseased forms, therefore he is developing different forms of body. There is no such case of Small-pox changing into Malaria. Small-pox is Small-pox, and Malaria is Malaria. By the desire of the living entity, he becomes infected with a certain disease or body. Krishna Consciousness is the vaccine for all the diseases (different forms of material bodies).