Now, this material creation is possible when the Supreme Spirit enters into it. This is a problem to the modern scientist, how creation was possible. They cannot understand that without spiritual touch, there cannot be any creation. That is their poor fund of knowledge. The Darwin's theory, development, process of evolution, they are childish. They are concentrating on the matter: matter is evolving. Matter does not evolve; matter is dead. It is due to the presence of the spirit soul it evolves. That they do not understand, although actually we are seeing. Just like a child born. If the child is born dead, it is simply dead matter. It does not grow. It is our practical experience. But if the child is living, or the spirit soul is within that body, then it develops. Similarly, 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 secretions, 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, biologists, 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 it is the fact.
Prabhupada's lecture - Śrīmad-Bhāgavatam 1.2.31 - Vṛndāvana, November 10, 1972