The soul or germ of life, after passing through the lower stages, comes to the human plane and gains experience and knowledge; and after coming to the human plane, it does not retrograde to animal bodies. The Platonic theory teaches that human souls migrate into animal bodies or angelic bodies and return from the angelic to the human or the animal, and that some of them prefer to become animals; while the theory of Reincarnation, taking its stand upon the scientific truth of gradual evolution, teaches that the human souls have already passed through different grades of the animal, nay, of the vegetable kingdom, by the natural process of evolution.
After having once received the human organism, why should a soul choose to go back to the lesser and more imperfect organism of an animal? How is it possible for a lesser manifestation to hold a greater one? Why should a greater manifestation choose more limited forms in preference to those of others? This question arises in the Platonic theory of Transmigration.
Therefore, the Reincarnation theory, or the theory of Transmigration according to the Hindus, rejects this idea of the going back of human souls to animal forms. We have already passed in the evolutionary process through the lower grade of animal organisms. Now that we have outgrown them why should we go back to them?
It is true, however, that in India there are many uneducated people among the Hindus who believe that human souls do migrate into animal bodies after death to gain experience and reap the results of their wicked deeds, being bound by the law of Karma; but in the Platonic theory the law of Karma plays no part in the transmigration of souls. The educated and thoughtful minds of India, however, accept the more rational and scientific theory of Reincarnation. Although there are passages in the scriptural writings of the Hindus which apparently refer to the retrogression of the human soul into animal nature, still such passages do not necessarily mean that the souls will be obliged to take animal bodies.
They may live like animals even when they have human bodies, as we may find among us many people like cats and dogs and snakes in human form and they are often more vicious than natural cats, dogs or snakes. They are reaping their own Karma and manifesting their animal nature, though physically they look like human beings. This kind of retrogression is possible for one who after reaching the human plane goes backward on account of wicked thoughts and deeds on the animal plane. Such a temporary retrogression brings knowledge and helps it in its onward progress toward the manifestation of higher powers on the higher plane of consciousness. All the wicked thoughts and wicked deeds are nothing but the results of our own mistakes.
What is sin? Sin is nothing but a mistake and it proceeds from ignorance. For instance, if I do not know that fire burns, I may put my finger into it and get burned. The result of this mistake is the burning of the finger and this has taught me once for all that fire burns; I shall never again put my finger into fire. So every mistake is a great teacher in the long run. No one is born so high and perfect as not to commit any mistake or any sin.
Every mistake like this opens our eyes to the laws of the universe by bringing to us such results as we do not desire. As one life is not enough to gain experience in all the stages of evolution, we must have to admit the doctrine of the Reincarnation of the soul for the fulfillment of the ultimate purpose of earthly life. Professor Huxley says: “None but hasty thinkers will reject it on the ground of inherent absurdity. Like the doctrine of evolution itself that of transmigration has its roots in the world of reality.”