Don't associate with this material nature. If you associate with this material nature, then what will be the result? Now, kāraṇaṁ guṇa-saṅgo 'sya sad-asad-yoni-janmasu (BG 13.22). Yoni means the source of birth. Just like we take our birth, the source is the mother. From the mother's womb we come out. That is called yoni, the source. The source is the mother. From the mother's womb we come out. That is called yoni, the source. So there are mothers—human being mother, cat mother, dog mother, this mother, so many mothers. Without mother there is no birth. And without father also, there is no birth. Therefore it is said that janame janame saba pitā mātā pāya. In every birth you will get a father and mother, because without father and mother there is no question of birth.
So here also see, sad-asad-yoni-janmasu. Why one is being born through the mother of a cat or through the mother of dog or a human being or a king or a demigod? The mother, through mother you have to come out. That is called yoni. But why these different mothers? Kāraṇaṁ guṇa-saṅgo 'sya. As he has infected the eighty-one qualities, colorful qualities of this material nature, the nature will give you a suitable body through the particular mother.
So where is this science? They have the botanical garden, but do they know what is the science why there is tree and why there is ant, why there is bird, why there is man? They have no knowledge. This material school, college, university, simply producing ordinary animal life. Actual knowledge is here in the Bhagavad-gītā. These are the . . . why one is forced to accept a certain type of body? Because after death I will have to accept a certain type of body. That is natural. Tathā dehāntara-prāptiḥ (BG 2.13). As I am getting dehāntara, one body after another, baby's body, then another body, child's body, then another body, boy's body . . . you may say: "It is growing." Growing or not growing, it is another body. Try to understand this. This child is playing. Now he will get another body when he will be called boy. He will get another body when he will be called youth. He will get another body when he will be called old man. So why not another body? This is called transmigration of the soul. Very simple thing.