The whole cosmic manifestation, this big universe, unless there is, in the center, the Supreme Spirit, how it develops? It cannot develop. Either you take this body or take this universal body—without the spirit being entered within it, there cannot be development.
The modern scientists, they have no knowledge. They cannot understand this. They are so poor fund of knowledge. Practically we are seeing every day. This body has developed, your body, my body, how it has developed? Because I, the spirit soul, you, the spirit soul, enter into the matter. Therefore it has developed. Karmaṇā daiva-netreṇa jantur deha upapattaye (SB 3.31.1).
So deha upapatti, development of this body, is possible when the spirit soul enters. The man, the male and female, they have sex life, and the two secretion, they mix up, becomes emulsified, and the spirit soul takes shelter within that matter. And then the matter develops gradually. That is the development within the embryo. And when it is fully developed, with hands and legs, consciousness, at seven months, then child wants to come out.
Then, by the natural process, on the tenth month the child comes out. But medical science or physiologist, biologist, they do not know this. They do not know this. They cannot explain how the body is developing, how the body is being formed. They do not know. But this is the fact. Tayā vilasiteṣu guṇeṣu guṇavān iva.
Now, the living entity wanted to enjoy this material world. We get different types of bodies on account of our desire to have such body. We want to enjoy the material . . . the matter in a certain way, and Kṛṣṇa gives us the opportunity to enjoy as we liked. Prakṛteḥ kriyamāṇāni guṇaiḥ karmāṇi sarvaśaḥ (BG 3.27).