"As explained in Bhagavad-gītā, it is not by any father or mother that the living entity is given his birth. The living entity is a completely separate identity from the so-called father and mother. By the laws of nature, the living entity is forced to enter the semen of a father and be injected into the womb of the mother. He is not in control of selecting what kind of father he will accept. prakṛteḥ kriyamāṇāni: (BG 3.27) the laws of nature force him to go to different fathers and mothers, just like a consumer commodity that is purchased and sold. Therefore the so-called relationship of father and son is an arrangement of prakṛti, or nature. It has no meaning, and therefore it is called illusion.
The same living entity sometimes takes shelter of an animal father and mother and sometimes a human father and mother. Sometimes he accepts a father and mother among the birds, and sometimes he accepts a demigod father and mother. Śrī Caitanya Mahāprabhu therefore says:
brahmāṇḍa bhramite kona bhāgyavān jīva
guru-kṛṣṇa-prasāde pāya bhakti-latā-bīja
(CC Madhya 19.151)
Harassed life after life by the laws of nature, the living entity wanders throughout the entire universe in different planets and different species of life. Somehow or other, if he is fortunate enough, he comes in touch with a devotee who reforms his entire life. Then the living entity goes back home, back to Godhead. Therefore it is said:
janame janame sabe pitā mātā pāya
kṛṣṇa guru nahi mile baja hari ei
In the transmigration of the soul through different bodies, everyone, in every form of life—be it human, animal, tree or demigod—gets a father and mother. This is not very difficult. The difficulty is to obtain a bona fide spiritual master and Kṛṣṇa. Therefore the duty of a human being is to capture the opportunity to come in touch with Kṛṣṇa's representative, the bona fide spiritual master. Under the guidance of the spiritual master, the spiritual father, one can return home, back to Godhead."
(Śrīmad-Bhāgavatam 6.16.6, Purport)