On the Creation of the World (161-162)

Now, the first approaches of the male to the female have a pleasure in them which brings on other pleasures also, and it is through this pleasure that the formation and generation of children is carried on. And what is generated by it appears to be attached to nothing rather than to it, since they rejoice in pleasure, and are impatient at pain, which is its contrary. On which account even the infant when first brought forth cries, being as it seems in pain at the cold. For coming forth on a sudden into the air from a very warm, and indeed, hot region—namely, the womb, in which it has been abiding a considerable time, the air being a cold place and one to which it is wholly unaccustomed, it is alarmed, and pours forth tears as the most evident proof of its grief and of its impatience at pain.

For every animal, it is said, hastens to pleasure as to the cud which is most indispensable and necessary to its very existence; and, above all other animals, this is the case with man. For other animals pursue pleasure only in taste and in the acts of generation; but man aims at it by means of his other senses also, devoting himself to whatever sights or sounds can impart pleasure to his eyes or ears.