He who knows more and more clearly, the self obtains fuller being. In plants and trees, sap only is seen, in animals only consciousness. The self is more and more clear in man for he is most endowed with intelligence. He knows tomorrow, he knows the world and what is not the world. By the mortal he desires the immortal, being thus endowed. As for animals, hunger and thirst comprise their knowledge. But this man is the sea, he is above the world. Whatever he reaches he desires to go beyond it.
Aitareya Aranyaka (II. I.3)