There are three modes of material nature—goodness, passion and ignorance. So long we are in this material world, puruṣaḥ prakṛti-stho 'pi bhuñjante tad-guṇān. If we remain in certain place, we must be affected by the modes of that place. So there are three modes: sattva-guṇa, rajo-guṇa . . . we have to associate either with the modes of goodness or with the modes of passion or with the modes of passion, er, ignorance. Now, three into three, it becomes nine, and nine into nine, it becomes eighty-one. So mixture. Just like color. There are three colors: blue, red and yellow. Now, those who are expert in manufacturing color, artists, they mix these three colors in different way and they display.
Similarly, according to the guṇas or mixture, association—kāraṇaṁ guṇa-saṅgo 'sya—we get different types of bodies. Therefore we see so many varieties of bodies. Kāraṇaṁ guṇa-saṅgo 'sya (BG 13.22). So the person who is taking very much pleasure, dancing in the sea like fish, so he is contaminating that modes of nature so that in next life he will become a fish. He'll be very free to dance with the ocean. (laughter)
Now it will take again millions of years to come to the stage of human being. Jalajā nava-lakṣāṇi sthāvarā lakṣa-viṁśati (Viṣṇu Purāṇa). He has to pass through the fish life. There are 900,000 different species of life. Then you again come to the land—you become trees, plants and so on. Two millions different forms you have to go through. That is evolution. Darwin's theory of evolution, that is not perfectly explained. It is explained in the Vedic literature.