The fruitive activities a living being performs, whether pious or impious, are the unseen cause for the fulfillment of his desires. This unseen cause is the root for the living entity’s different bodies. Because of his intense desire, the living entity takes birth in a particular family and receives a body which is either like that of his mother or like that of his father. The gross and subtle bodies are created according to his desire.
Srimad Bhagavata Purana
श्रीमद्भागवतमहापुराणम्
मूल श्लोकः
लब्ध्वा निमित्तमव्यक्तं व्यक्ताव्यक्तं भवत्युत । यथायोनि यथाबीजं स्वभावेन बलीयसा
labdhvā nimittamavyaktaṃ vyaktāvyaktaṃ bhavatyuta | yathāyoni yathābījaṃ svabhāvena balīyasā
SB 6.1.54