A father is merely an instrumental cause (touching the generation of his child). A father's semen coming in contact with a mother's blood, at the time befitting conception, a person is brought into being.
बीजमात्रं पिता जन्तोः शुक्रं शोणितमेव च। संयुक्तमृतुमन्मात्रा पुरुषस्येह जन्म तत्॥