The process of birth is determined by one's karma. In the early texts the process of birth is merely described, and not explained:
When he has suffered through all the hells, the sinner, through the ripening of his own karma that he committed even while inside another body, enters the animal creation, among wonns, insects, and birds; among wild animals, mosquitoes, and so forth; among elephants, trees [sic], cattle, and horses, and other evil and harmfull creatures. Then he is born as a man, a contemptible one like a hunchback or a dwarf; among Candalas, Pullkasas, and so forth. And then, accompanied by his remaining sins and merits, he enters the classes in ascending order - Sudra, Vaisya, king, and so forth - and then he becomes a Brahmin, a god, and an Indra. But sometimes he does it in descending order, and evil-doers fall down into hell"40.
Jiva (the subtle body which is attached to atman) is born as man, when a woman gets impregnated by a man.
Impregnation of a woman by a man takes place when the seed is placed in her blood; as soon as it is discharged from heaven or hell, it sets out.... The embryo remembers its many transmigrations, and it is distressed because of this one and that one, and therefore it becomes depressed41.
At the time of the faIling of the seed of the man, a portion of the jiva (,/ivarmsa) grows in the pregnant womb, by means of blood. From the entry of the man's jiva into the womb, flesh accrues42
Here it is apparent that the jiva is given by the man and nourished by the woman, a view upheld in most of the medical and legal texts. Other Puranas indicate a more equal division of responsibility between man and woman: "... In the union of a woman and a man he is born"43.
In the womb of the mother, the jiva remembers all its past lives and his karmas, both good and bad, the joys and sorrows of his previous actions, but at birth it is deluded by the force of maya and forgets his former lives. Thus the newborn child is unaware of his accumulated karma, but is predetermined by his karma: "By his own karmas a creature becomes a god, man, animal, bird, or immovable thing".44 "By good deeds one becomes a god; by bad deeds a creature is born among animals and by mixed deeds, a mortal. The Veda (sruti) is the authority for the distinction between nrmn and ndharma "45
It is therefore jiva which has still to pay its adharma (karma) that incarnates or transmigrates as man. Consciousness (caitanya), desire, thought are inherent in the jiva which takes a material form in the womb of a woman 46