According to Vedanta, the end and aim of Evolution is the attainment of perfection. Physical evolution of animal life reached its perfection in human form. There cannot be any other form higher than human on this earth under present conditions. It is the perfection of animal form. From this we can infer that the tendency of the law of Evolution is to reach perfection.
When it is attained to, the whole purpose is served. Do we see in nature any other higher form evolved out of the human body? No. Shall we not be justified if we say that the end of physical evolution is the attainment of the perfection of animal form? Again as the purpose and method of natural laws are uniform throughout the universe, the end of intellectual, moral and spiritual evolution will be attained when intellectual, moral and spiritual perfection are acquired. Intellectual perfection means perfection of intellect; and intellect is perfect when we understand the true nature of things and never mistake the unreal for the real, matter for spirit, non-eternal for eternal, or vice versa. Moral perfection consists in the destruction of selfishness; and spiritual perfection is the manifestation of the true nature of spirit which is immortal, free, divine and one with the Universal Spirit or God. Evolution attains to the highest fulfilment of its purpose when the spirit manifests perfectly.
The tendency of nature is to have perfect manifestation of all her powers. When certain powers predominate they manifest first while the others remain dormant. As we find in the process of evolution, when animal nature manifests perfectly the moral and spiritual nature remain latent. Again when moral and spiritual nature manifest fully, the animal is in abeyance. It is for this reason we do not find expressions of moral and spiritual nature in lower animals or in those human beings who live like them.
Man is the only animal in whom such perfect expressions of moral and spiritual nature are possible. When the individual soul begins to study its spiritual nature, its lower or animal nature is gradually eclipsed. As the higher nature becomes powerful the lower nature dwindles into insignificance; its energy is transformed into that of the higher nature, and ultimately it disappears altogether and rises no more. Then the soul becomes free from the lower or animal nature. There are many stages in the higher nature, as well as in the lower. Each of these stages binds the individual soul so long as it stays there. As it rises on a higher plane the lower stages disappear and cease to bind. But the moment that any individual, after passing through all the stages of the spiritual nature, reaches the ultimate point of perfection, he realizes his true nature which is immortal and divine. Then his true individuality manifests.
For lack of true knowledge, he identified himself with each stage successively and thought that his individuality was one with the powers which were manifested in each stage. Consequently he thought by mistake that he was affected by the changes of each stage. But now he realizes that his real individuality always remained unaffected. He sees that his true individuality shines always in the same manner, although the limiting adjuncts may vary. As the light of a lamp appears of different colors, if it passes through glasses of different colors, so the light of the true individual appears as animal or human when it passes through the animal or human nature of the subtle body.
The subtle body of an individual changes from animal nature through moral and spiritual into divine. As this gradual growth cannot be expected in one life we shall have to admit the truth of Reincarnation, which teaches gradual evolution of the germ of life or the individual soul through many lives and various forms. Otherwise the theory of Evolution will remain imperfect, incomplete and purposeless. The doctrine of Reincarnation differs from the accepted theory of Evolution in admitting a gradual but continuous evolution of the subtle body through many gross forms. The gross body may appear or disappear, but the subtle body continues to exist even after the dissolution of the gross body and re-manifests itself in some other form.