According to Garuda Purana, it is not the karma or the jiva alone that determines birth and nature but the consciousness of the father at the time of impregnation. "Whatever a man has on his mind at the time of impregnation, a creature born of such a nature (svabhava) will enter the womb',47
This, naturally, brings up the question of the role of the karma of the parents in the process of rebirth. The Puranas state that the child's birth is affected by the karma of the father and the mother;48 similarly, the embryo's physical makeup is contributed by both parents: the mother gives hair, nails, skin, flesh and the father gives bone, sinew, and marrow49. The actual mechanism of this karmic transfer during the process of birth is not explained in the Puranas, but the effect of it is certainly taken for granted; and the transfer of karma in the opposite direction (from child to parent) takes place often during life and after the death of the parent.
Both in the Mahabharata and in the Puranas, we find myths illustrative of the karma flow in both directions: from living children to dead ancestors (as in the tale of a sage's ancestors hanging by their fingertips in a great pit - Mahabharata 3.94-97); and, less often, from parents to children. [A series of karmic transfers from children to parents takes place between King Yayati and his sons and grandsons.50 In the myth of Vena, karma flows in both directions: the evil of Vena himself is the result of the direct transfer of negative karma from his evil mother - who is evil because of the karma inherited from her father, death;5i but when Vena dies, and is reborn as a leper, his good son Prthu saves him by going to a shrine, performing a ritual, and transferring that merit to his father, for his father is so impure that he would transfer his own bad karma to the shrine and thus defile it; only the devotional sacrifice of the son can save him.52 In other texts, Vena is saved simply by the birth of his good son,53 or, in a more primitive process, by the birth of an evil son, who draws the evil out of Vena in a direct transfer,54 as the evil demon drew the evil nature out of the Brahmin's wife. Thus evil karma is transferred from parent to child in a direct line, thus explaining the existence of evil in the present; good karma is transferred backwards into the past and into the future, through the heteropathic devotion of the good child to the evil parent - the ritual model of the sraddha offering, translated into bhakti mythology.]