In the material world, material nature displays wonderful workmanship by creating varieties of bodies for the living beings according to their propensities for sense gratification. The living entity who wants to taste stool is given a material body that is quite suitable for eating stool—that of a hog. Similarly, one who wants to eat the flesh and blood of other animals may be given a tiger's body equipped with suitable teeth and claws. But the human being is not meant for eating flesh, nor does he have any desire to taste stool, even in the most aboriginal state. Human teeth are so made that they can chew and cut fruit and vegetables, although there are two canine teeth so that primitive humans can eat flesh if they so desire.
But in any case, the material bodies of all animals and men are foreign to the living entity. They change according to the living entity's desire for sense gratification. In the cycle of evolution, the living entity changes bodies one after another. When the world was full of water, the living entity took an aquatic form. Then he passed to vegetable life, from vegetable life to worm life, from worm life to bird life, from bird life to animal life, and from animal life to the human form. The highest developed form is this human form when it is possessed of a full sense of spiritual knowledge. The highest development of one's spiritual sense is described in this mantra: One should give up the material body, which will be turned to ashes, and allow the air of life to merge into the eternal reservoir of air. The living being's activities are performed within the body through the movements of different kinds of air, known in summary as prāṇa-vāyu. The yogīs generally study how to control the airs of the body. The soul is supposed to rise from one circle of air to another until it rises to the brahma-randhra, the highest circle. From that point the perfect yogī can transfer himself to any planet he likes. The process is to give up one material body and then enter into another. But the highest perfection of such changes occurs only when the living entity is able to give up the material body altogether, as suggested in this mantra, and enter into the spiritual atmosphere, where he can develop a completely different type of body-a spiritual body, which never has to meet death or change.
Here in the material world, material nature forces the living entity to change his body due to his different desires for sense gratification. These desires are represented in the various species of life, from germs to the most perfected material bodies, those of Brahmā and the demigods. All of these living entities have bodies composed of matter in different shapes. The intelligent man sees oneness not in the variety of the bodies but in the spiritual identity. The spiritual spark, which is part and parcel of the Supreme Lord, is the same whether he is in a body of a hog or in the body of a demigod. The living entity takes on different bodies according to his pious and vicious activities. The human body is highly developed and has full consciousness. According to the Bhagavad-gītā (7.19), the most perfect man surrenders unto the Lord after many, many lifetimes of culturing knowledge. The culture of knowledge reaches perfection only when the knower comes to the point of surrendering unto the Supreme Lord, Vāsudeva. Otherwise, even after attaining knowledge of one's spiritual identity, if one does not come to the point of knowing that the living entities are eternal parts and parcels of the whole and can never become the whole, one has to fall down again into the material atmosphere. Indeed, one must fall down even if he has become one with the brahmajyoti.
As we have learned from previous mantras, the brahmajyoti emanating from the transcendental body of the Lord is full of spiritual sparks that are individual entities with the full sense of existence. Sometimes these living entities want to enjoy their senses, and therefore they are placed in the material world to become false lords under the dictation of the senses. The desire for lordship is the material disease of the living being, for under the spell of sense enjoyment he transmigrates through the various bodies manifested in the material world. Becoming one with the brahmajyoti does not represent mature knowledge. Only by surrendering unto the Lord completely and developing one's sense of spiritual service does one reach the highest perfectional stage.